Works

20260217_212053_z        set RTC to GPS using 1PPS pulse-per-second discipline  rtc-gps drift=+0 s; sats=20; lat=44.936488 lon=-123.021837; alt_m=59.1; hdop=0.7; utc_age_ms=659; pps_edges=805; fw_epoch=1771362221; fw_build_utc=20260217_210341_z

.gitignore

@@ -0,0 +1,20 @@
+/build/
+/provisioning/
+/*.log
+.pio/
+.pio
+.vscode/
+*.elf
+*.bin
+*.map
+# Emacs backup files
+*~
+\#*\#
+.\#*
+
+# Emacs dir locals (optional)
+.dir-locals.el
+/hold/
+.platformio_local/
+
+.codex

.gitmodules

@@ -1,3 +1,15 @@
 [submodule "external/microReticulum"]
 	path = external/microReticulum
 	url = https://github.com/attermann/microReticulum.git
+[submodule "external/DebugLog"]
+	path = external/DebugLog
+	url = https://github.com/hideakitai/DebugLog.git
+[submodule "external/ArxTypeTraits"]
+	path = external/ArxTypeTraits
+	url = https://github.com/hideakitai/ArxTypeTraits.git
+[submodule "external/ArxContainer"]
+	path = external/ArxContainer
+	url = https://github.com/hideakitai/ArxContainer.git
+[submodule "external/microReticulum_Firmware"]
+	path = external/microReticulum_Firmware
+	url = https://github.com/attermann/microReticulum_Firmware

CMakeLists.txt

@@ -0,0 +1,68 @@
+cmake_minimum_required(VERSION 3.16)
+project(microReticulumTbeam LANGUAGES C CXX)
+
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+# --------------------------------------------------------------------
+# Portability shims
+#
+# microReticulum's CMake currently links against "msgpackc-cxx" and "MsgPack"
+# as if they were system libraries, which breaks on machines that don't have
+# those exact libs installed.
+#
+# Define shim targets so CMake treats them as targets (no "-l...").
+# If/when you want a real msgpack-cxx dependency, replace the shim with
+# FetchContent/find_package and link to that instead.
+# --------------------------------------------------------------------
+if(NOT TARGET msgpackc-cxx)
+  add_library(msgpackc-cxx INTERFACE)
+endif()
+
+if(NOT TARGET MsgPack)
+  add_library(MsgPack INTERFACE)
+endif()
+
+
+# Pull in the microReticulum submodule build
+add_subdirectory(external/microReticulum)
+
+# Provide DebugLog.h for microReticulum's MsgPack dependency
+#set(DEBUGLOG_DIR ${CMAKE_SOURCE_DIR}/external/DebugLog)
+
+#if(TARGET ReticulumShared)
+#  target_include_directories(ReticulumShared PUBLIC ${DEBUGLOG_DIR})
+#endif()
+
+#if(TARGET ReticulumStatic)
+#  target_include_directories(ReticulumStatic PUBLIC ${DEBUGLOG_DIR})
+#endif()
+
+set(DEBUGLOG_DIR     ${CMAKE_SOURCE_DIR}/external/DebugLog)
+set(ARX_TYPETRAITS_DIR ${CMAKE_SOURCE_DIR}/external/ArxTypeTraits)
+set(ARX_CONTAINER_DIR   ${CMAKE_SOURCE_DIR}/external/ArxContainer)
+
+if(TARGET ReticulumShared)
+  target_include_directories(ReticulumShared PUBLIC
+    ${DEBUGLOG_DIR}
+    ${ARX_TYPETRAITS_DIR}
+    ${ARX_CONTAINER_DIR}
+  )
+endif()
+
+if(TARGET ReticulumStatic)
+  target_include_directories(ReticulumStatic PUBLIC
+    ${DEBUGLOG_DIR}
+    ${ARX_TYPETRAITS_DIR}
+    ${ARX_CONTAINER_DIR}
+  )
+endif()
+
+# We only need the static library for host-side tooling.
+# The shared lib target requires system msgpack libs on some systems.
+if(TARGET ReticulumShared)
+  set_target_properties(ReticulumShared PROPERTIES EXCLUDE_FROM_ALL YES)
+endif()
+
+# Build our host-side tools
+add_subdirectory(tools)

README.md

@@ -2,3 +2,14 @@
 microReticulum For Field Testing With LilyGo T-Beam SUPREMES
 
 Field Testing Only.  Used to specially program a group of T-Beams, each having the others' contact information and keys, which are then deployed in the field with people moving about to capture what was successfully sent and received and at what coordinates.  Data is stored on SD cards and then retrieved at the end of the test an dumped into a PostgreSQL databse for analysis.
+
+## Dependency Direction
+This repo is migrating from `external/microReticulum` to `external/microReticulum_Firmware`.
+
+Goal:
+- Reuse upstream T-Beam SUPREME integration work in `microReticulum_Firmware`.
+- Avoid reimplementing already-solved board integration (PMU, SD, RTC, GPS, LoRa setup).
+
+Status:
+- Migration plan is tracked in `docs/microreticulum_firmware_migration.md`.
+- Existing exercises remain functional during migration.

docs/gps.md

@@ -0,0 +1,18 @@
+The T-Beam ships with two options:
+1) L76K
+2) MAX-M10S
+   
+NMEA (National Marine Electronics Association) format is a standard protocol used for communication between marine electronics devices, including GPS receivers, chart plotters, and other navigation equipment. It's a text-based, ASCII-encoded format that transmits data in "sentences" — short, comma-separated strings that start with a dollar sign ($) and end with a checksum.
+
+Key Characteristics:
+Structure: Each sentence begins with $ followed by a talker ID (e.g., GP for GPS), a sentence type (e.g., GGA for Global Positioning System Fix Data), and data fields separated by commas. It ends with an asterisk (*) and a two-character hexadecimal checksum.
+Example: $GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47
+This is a GGA sentence providing time, latitude, longitude, fix quality, number of satellites, etc.
+Common Sentence Types (relevant to GPS):
+GGA: GPS fix data (position, time, satellites).
+RMC: Recommended minimum navigation information (position, speed, course).
+GSV: Satellites in view.
+TXT: Text messages (e.g., module identification).
+Baud Rate: Typically transmitted at 4800 or 9600 baud over serial interfaces.
+Usage: Widely used in GPS modules like the L76K and UBLOX MAX-M10S, as seen in your project's code where NMEA sentences are parsed to extract location, time, and satellite data.
+In your T-Beam exercises, the code reads serial data from the GPS module, buffers it into lines, and parses these NMEA sentences to detect the module type and extract useful information like UTC time and satellite counts. Both L76K and UBLOX modules output NMEA by default, though UBLOX can also support other formats like UBX binary. If you need details on parsing specific sentences or differences between modules, let me know!

docs/microreticulum_firmware_migration.md

@@ -0,0 +1,45 @@
+# microReticulum Firmware Migration Plan
+
+## Objective
+Migrate this project from the current submodule:
+- `external/microReticulum`
+
+to:
+- `external/microReticulum_Firmware`
+
+so this repo consumes existing T-Beam SUPREME integration instead of duplicating it.
+
+## Current State
+- `.gitmodules` currently declares `external/microReticulum`.
+- `.gitmodules` now also declares `external/microReticulum_Firmware`:
+  - URL: `https://github.com/attermann/microReticulum_Firmware`
+  - Current commit: `5dc607fc7227c46ccb19244e456782fbb7775eae`
+- Exercises under `exercises/` are self-contained and currently compile independently.
+
+## Planned Migration Steps
+1. Add the new submodule at `external/microReticulum_Firmware`.
+2. Keep `external/microReticulum` temporarily for side-by-side validation.
+3. Inventory reusable components from `microReticulum_Firmware`:
+   - board init / PMU power sequencing
+   - LoRa interface setup
+   - SD/RTC/GPS integration glue
+4. Refactor local firmware entry points to call upstream components where possible.
+5. Update exercise docs to distinguish:
+   - hardware smoke tests (local exercises)
+   - integration paths (from `microReticulum_Firmware`)
+6. After parity validation, remove or archive `external/microReticulum`.
+
+Step-2 inventory output:
+- `docs/microreticulum_firmware_step2_adoption_matrix.md`
+
+## Validation Checklist
+- Build passes for all key exercises.
+- SD/RTC/GPS startup behavior remains stable.
+- LoRa send/receive smoke tests still pass.
+- Fieldtest beacon path compiles and boots.
+
+## Submodule Commands Used
+```bash
+git submodule add https://github.com/attermann/microReticulum_Firmware external/microReticulum_Firmware
+git submodule update --init --recursive
+```

docs/microreticulum_firmware_step2_adoption_matrix.md

@@ -0,0 +1,62 @@
+# Step 2 Adoption Matrix
+
+## Scope
+Repository: `microReticulumTbeam`  
+Submodule source: `external/microReticulum_Firmware`
+
+## What Step 2 Means
+Identify and wire the first low-risk points where this repo should consume existing board-integration logic from `microReticulum_Firmware`, instead of maintaining duplicate local assumptions.
+
+## High-Value Upstream Sources
+- `external/microReticulum_Firmware/Boards.h`
+  - T-Beam Supreme pin map and feature flags.
+  - Includes SD pins (`SD_CS=47`, `SD_CLK=36`, `SD_MISO=37`, `SD_MOSI=35`), PMU I2C pins (`I2C_SDA=42`, `I2C_SCL=41`), LoRa pins.
+- `external/microReticulum_Firmware/Power.h`
+  - AXP2101 setup sequence for T-Beam Supreme (`BOARD_TBEAM_S_V1`), including SD rail (BLDO1), ALDO rails, charging config.
+- `external/microReticulum_Firmware/platformio.ini`
+  - `env:ttgo-t-beam-supreme` build model and dependency pattern.
+
+## Local Targets And First Consumers
+1. `firmware/fieldtest_beacon/src/main.cpp`
+- Why first: this is the integration entry point, not just a smoke test.
+- Step-2 change made: SD CS now comes from `Boards.h` instead of hardcoded `10`.
+
+2. `exercises/04_SD_card/src/main.cpp`
+- Why second: duplicates PMU + SD pin assumptions already present upstream.
+- Planned consume-first item: PMU rail setup pattern from `Power.h`.
+
+3. `exercises/05_SD_Card_Watcher/src/main.cpp`
+- Why third: extends `04` and should share the same PMU/pin source strategy.
+- Planned consume-first item: same board/power source as `04`.
+
+4. `exercises/06_RTC_check/src/main.cpp`
+- Why fourth: depends on PMU + I2C pin assumptions that overlap upstream.
+- Planned consume-first item: board I2C pin source and PMU readiness sequence.
+
+## Current Wiring Done
+- Added submodule:
+  - `external/microReticulum_Firmware`
+- Wired one concrete consumer:
+  - `firmware/fieldtest_beacon/src/main.cpp` now includes `Boards.h` and uses `SD_CS`.
+  - `firmware/fieldtest_beacon/platformio.ini` now includes `external/microReticulum_Firmware` headers and sets `BOARD_MODEL=BOARD_TBEAM_S_V1`.
+- Added local adapter:
+  - `shared/boards/tbeam_supreme_adapter.h`
+  - Exposes board pins and PMU setup based on upstream T-Beam Supreme definitions.
+- Refactored exercises to consume adapter:
+  - `exercises/04_SD_card`
+  - `exercises/05_SD_Card_Watcher`
+  - `exercises/06_RTC_check`
+
+## Validation Status
+- `firmware/fieldtest_beacon` now builds after adding required deps:
+  - `ArduinoJson` 7.x
+  - `MsgPack`
+  - `Crypto` (provides `Ed25519.h` and `Curve25519.h`)
+- `exercises/04_SD_card` builds.
+- `exercises/05_SD_Card_Watcher` builds.
+- `exercises/06_RTC_check` builds.
+
+## Next Step Candidate
+Reduce macro redefinition warnings emitted by `Boards.h` in adapter consumers:
+- Option A: small local board-map header with only required constants copied from upstream board model.
+- Option B: upstream contribution to make board capability macros conditional/override-safe.

docs/pio.md

@@ -0,0 +1,141 @@
+# pio
+pio stands for "PlatformIO".  
+
+In your context (ESP32 / T-Beam / PlatformIO workflows), **“pio” stands for:**
+
+> **PlatformIO**
+
+More precisely, `pio` is the **command-line interface (CLI)** for the PlatformIO environment.
+
+---
+
+## What PlatformIO is (practically speaking)
+
+PlatformIO is an embedded development framework that wraps:
+
+* toolchains (GCC for ESP32, ARM, etc.)
+* build system
+* library manager
+* uploader (esptool, etc.)
+* serial monitor
+
+So instead of juggling:
+
+```bash
+xtensa-esp32-elf-gcc
+esptool.py
+arduino-cli
+```
+
+…you use:
+
+```bash
+pio run
+pio run -t upload
+pio device monitor
+```
+
+---
+
+## What `pio` actually does in your workflow
+
+Given your T-Beam usage (as shown in the LilyGO docs, which explicitly include PlatformIO as a supported environment ), `pio` is orchestrating:
+
+### Build
+
+```bash
+pio run
+```
+
+* compiles your firmware using the environment in `platformio.ini`
+
+### Upload
+
+```bash
+pio run -t upload
+```
+
+* invokes the correct uploader (ESP32 → `esptool`)
+* uses the selected `/dev/tty*` device
+
+### Monitor
+
+```bash
+pio device monitor
+```
+
+* serial console at configured baud
+
+---
+
+## Why it exists (the “systems view”)
+
+PlatformIO abstracts away:
+
+* board definitions
+* pin mappings
+* compiler flags
+* library dependencies
+
+In your `platformio.ini`, for example:
+
+```ini
+[env:node_a]
+platform = espressif32
+board = esp32-s3-devkitc-1
+```
+
+That single block drives:
+
+* toolchain selection
+* linker scripts
+* upload protocol
+* memory layout
+
+---
+
+## Important nuance (since you’re working low-level)
+
+`pio` is **not**:
+
+* a compiler
+* a flasher
+* an IDE
+
+It is a **build orchestration layer** (think “make + package manager + uploader + board database”).
+
+---
+
+## Quick mental model
+
+If we translate to Unix analogies:
+
+| Concept             | Analogy                                      |
+| ------------------- | -------------------------------------------- |
+| PlatformIO          | `portage + make + gcc + flash tool` combined |
+| `pio run`           | `make`                                       |
+| `pio run -t upload` | `make install` (but to hardware)             |
+| `platformio.ini`    | hybrid of `Makefile` + config                |
+
+---
+
+## Bottom line
+
+When you type:
+
+```bash
+pio run -t upload
+```
+
+You are saying:
+
+> “Use PlatformIO to build this firmware for the specified environment and flash it to the target device.”
+
+
+## PlatformIO configuration file
+platformio.ini is the configuration file.  Each unit should have it's own entry so that the code can automaticaly be modified.
+
+INSERT IMAGE
+
+## Uploading Image
+pio run -e flo -t upload --upload-port /dev/ttytFLO

exercises/00_usb_radio_check/README.md

@@ -0,0 +1,116 @@
+Command:
+
+     pio run -e node_a -t upload --upload-port /dev/ttyACM0
+Here's a sample compile & upload session:
+
+    (rnsenv) jlpoole@jp /usr/local/src/microreticulum/microReticulumTbeam/exercises/00_usb_radio_check $ pio run -e node_a -t upload --upload-port /dev/ttyACM0
+    Processing node_a (platform: espressif32; framework: arduino; board: esp32-s3-devkitc-1)
+    ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+    Verbose mode can be enabled via `-v, --verbose` option
+    CONFIGURATION: https://docs.platformio.org/page/boards/espressif32/esp32-s3-devkitc-1.html
+    PLATFORM: Espressif 32 (6.12.0) > Espressif ESP32-S3-DevKitC-1-N8 (8 MB QD, No PSRAM)
+    HARDWARE: ESP32S3 240MHz, 320KB RAM, 8MB Flash
+    DEBUG: Current (esp-builtin) On-board (esp-builtin) External (cmsis-dap, esp-bridge, esp-prog, iot-bus-jtag, jlink, minimodule, olimex-arm-usb-ocd, olimex-arm-usb-ocd-h, olimex-arm-usb-tiny-h, olimex-jtag-tiny, tumpa)
+    PACKAGES: 
+    - framework-arduinoespressif32 @ 3.20017.241212+sha.dcc1105b 
+    - tool-esptoolpy @ 2.40900.250804 (4.9.0) 
+    - tool-mkfatfs @ 2.0.1 
+    - tool-mklittlefs @ 1.203.210628 (2.3) 
+    - tool-mkspiffs @ 2.230.0 (2.30) 
+    - toolchain-riscv32-esp @ 8.4.0+2021r2-patch5 
+    - toolchain-xtensa-esp32s3 @ 8.4.0+2021r2-patch5
+    LDF: Library Dependency Finder -> https://bit.ly/configure-pio-ldf
+    LDF Modes: Finder ~ chain, Compatibility ~ soft
+    Found 34 compatible libraries
+    Scanning dependencies...
+    Dependency Graph
+    |-- RadioLib @ 6.6.0
+    |-- SPI @ 2.0.0
+    Building in release mode
+    Retrieving maximum program size .pio/build/node_a/firmware.elf
+    Checking size .pio/build/node_a/firmware.elf
+    Advanced Memory Usage is available via "PlatformIO Home > Project Inspect"
+    RAM:   [=         ]   6.0% (used 19768 bytes from 327680 bytes)
+    Flash: [=         ]   8.8% (used 294065 bytes from 3342336 bytes)
+    Configuring upload protocol...
+    AVAILABLE: cmsis-dap, esp-bridge, esp-builtin, esp-prog, espota, esptool, iot-bus-jtag, jlink, minimodule, olimex-arm-usb-ocd, olimex-arm-usb-ocd-h, olimex-arm-usb-tiny-h, olimex-jtag-tiny, tumpa
+    CURRENT: upload_protocol = esptool
+    Looking for upload port...
+    Using manually specified: /dev/ttyACM0
+    Uploading .pio/build/node_a/firmware.bin
+    esptool.py v4.9.0
+    Serial port /dev/ttyACM0
+    Connecting...
+    Chip is ESP32-S3 (QFN56) (revision v0.2)
+    Features: WiFi, BLE, Embedded Flash 8MB (GD)
+    Crystal is 40MHz
+    USB mode: USB-Serial/JTAG
+    MAC: 48:ca:43:5a:93:a0
+    Uploading stub...
+    Running stub...
+    Stub running...
+    Changing baud rate to 460800
+    Changed.
+    Configuring flash size...
+    Flash will be erased from 0x00000000 to 0x00003fff...
+    Flash will be erased from 0x00008000 to 0x00008fff...
+    Flash will be erased from 0x0000e000 to 0x0000ffff...
+    Flash will be erased from 0x00010000 to 0x00057fff...
+    SHA digest in image updated
+    Compressed 15104 bytes to 10430...
+    Writing at 0x00000000... (100 %)
+    Wrote 15104 bytes (10430 compressed) at 0x00000000 in 0.2 seconds (effective 519.1 kbit/s)...
+    Hash of data verified.
+    Compressed 3072 bytes to 146...
+    Writing at 0x00008000... (100 %)
+    Wrote 3072 bytes (146 compressed) at 0x00008000 in 0.0 seconds (effective 584.3 kbit/s)...
+    Hash of data verified.
+    Compressed 8192 bytes to 47...
+    Writing at 0x0000e000... (100 %)
+    Wrote 8192 bytes (47 compressed) at 0x0000e000 in 0.1 seconds (effective 721.9 kbit/s)...
+    Hash of data verified.
+    Compressed 294432 bytes to 164378...
+    Writing at 0x00010000... (9 %)
+    Writing at 0x0001bc31... (18 %)
+    Writing at 0x00024a76... (27 %)
+    Writing at 0x0002a8b3... (36 %)
+    Writing at 0x0002fd85... (45 %)
+    Writing at 0x000350b4... (54 %)
+    Writing at 0x0003b4b4... (63 %)
+    Writing at 0x000455f6... (72 %)
+    Writing at 0x0004c5eb... (81 %)
+    Writing at 0x00051c54... (90 %)
+    Writing at 0x00057b42... (100 %)
+    Wrote 294432 bytes (164378 compressed) at 0x00010000 in 1.9 seconds (effective 1241.1 kbit/s)...
+    Hash of data verified.
+
+    Leaving...
+    Hard resetting via RTS pin...
+    ==================================================================================== [SUCCESS] Took 8.73 seconds ====================================================================================
+
+    Environment    Status    Duration
+    -------------  --------  ------------
+    node_a         SUCCESS   00:00:08.731
+    ==================================================================================== 1 succeeded in 00:00:08.731 ====================================================================================
+    (rnsenv) jlpoole@jp /usr/local/src/microreticulum/microReticulumTbeam/exercises/00_usb_radio_check $
+
+Here's an example of what displays in the console:
+
+Booting LoRa test...
+
+Initializing radio...
+Radio chip: SX1262
+Frequency: 915.000 MHz
+SF: 7 BW: 125 CR: 5
+radio.begin returned: 0
+alive 0
+       Sending test frame...
+TX state: 0
+Starting receive...
+startReceive returned: 0
+alive 1
+       Sending test frame...
+TX state: 0
+Starting receive...
+startReceive returned: 0
+alive 2

exercises/00_usb_radio_check/platformio.ini

@@ -0,0 +1,43 @@
+; 20260212 ChatGPT
+; $Id$
+; $HeadURL$
+
+[platformio]
+default_envs = node_a
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+monitor_speed = 115200
+lib_deps =
+  jgromes/RadioLib@^6.6.0
+
+; Common build flags (pins from Meshtastic tbeam-s3-core variant.h)
+build_flags =
+  -D LORA_CS=10
+  -D LORA_MOSI=11
+  -D LORA_SCK=12
+  -D LORA_MISO=13
+  -D LORA_RESET=5
+  -D LORA_DIO1=1
+  -D LORA_BUSY=4
+  -D LORA_TCXO_VOLTAGE=1.8
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+
+; Radio params for println/printf + RadioLib init
+  -D LORA_FREQ=915.000
+  -D LORA_SF=7
+  -D LORA_BW=125
+  -D LORA_CR=5
+
+[env:node_a]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"A\"
+
+[env:node_b]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"B\"

exercises/00_usb_radio_check/src/main.cpp

@@ -0,0 +1,60 @@
+#include <Arduino.h>
+#include <SPI.h>
+#include <RadioLib.h>
+
+#ifndef LORA_FREQ
+#define LORA_FREQ 915.000
+#endif
+
+#ifndef LORA_SF
+#define LORA_SF 7
+#endif
+
+#ifndef LORA_BW
+#define LORA_BW 125
+#endif
+
+#ifndef LORA_CR
+#define LORA_CR 5
+#endif
+
+
+// SX1262 on T-Beam Supreme (tbeam-s3-core pinout)
+SX1262 radio = new Module(LORA_CS, LORA_DIO1, LORA_RESET, LORA_BUSY);
+int state; // = radio.begin(915.0, 125.0, 7, 5, 0x12, 14);
+
+void setup() {
+  Serial.begin(115200);
+  delay(2000);   // give USB time to enumerate
+  Serial.println("Booting LoRa test...");
+  Serial.println();
+
+  Serial.println("Initializing radio...");
+  SPI.begin(LORA_SCK, LORA_MISO, LORA_MOSI, LORA_CS);
+  Serial.printf("Radio chip: SX1262\r\n");
+  Serial.printf("Frequency: %.3f MHz\r\n", (double)LORA_FREQ);
+  Serial.printf("SF: %d BW: %d CR: %d\r\n", LORA_SF, LORA_BW, LORA_CR);
+
+  int state = radio.begin(915.0, 125.0, 7, 5, 0x12, 14);
+  
+  Serial.printf("radio.begin returned: %d\r\n", state);
+
+
+
+}
+
+void loop() {
+  static uint32_t counter = 0;
+  Serial.printf("alive %lu\n", counter++);
+  
+  Serial.println("Sending test frame...");
+  int tx = radio.transmit("USB RADIO CHECK");
+  Serial.printf("TX state: %d\r\n", tx);
+
+  // we're not expecting to receive anything, just testing that we
+  // can call Receive()
+  Serial.println("Starting receive...");
+  state = radio.startReceive();
+  Serial.printf("startReceive returned: %d\r\n", state);
+  delay(1000);
+}

exercises/01_lora_ascii_pingpong/README.md

@@ -0,0 +1,249 @@
+# Exercise: LoRa Transmission Validation (SX1262)
+
+## Overview
+
+This exercise validates raw LoRa packet transmission from the **LILYGO T-Beam SUPREME V3.0** using the onboard **SX1262** radio.
+
+The objective is to:
+
+1. Transmit deterministic LoRa packets at known parameters.
+2. Confirm successful reception using:
+
+   * A second T-Beam
+   * A Waveshare SX1303 concentrator sniffer
+   * Or any SDR/LoRa receiver configured with identical PHY settings
+3. Verify correct alignment of frequency, spreading factor, bandwidth, and coding rate.
+
+This is a **PHY-layer validation exercise**, not LoRaWAN.
+
+---
+
+## Hardware
+
+### Transmitter
+
+* Board: **LILYGO T-Beam SUPREME V3.0**
+* MCU: ESP32-S3
+* Radio: SX1262
+* Antenna: 915 MHz tuned antenna
+* Power: USB-C or 18650 battery
+
+### Receiver / Sniffer
+
+Any device capable of raw LoRa reception with manual PHY configuration:
+
+* Second T-Beam (SX1262)
+* Waveshare SX1303 + `lora_pkt_fwd`
+* SDR with LoRa demodulator
+
+---
+
+## LoRa Radio Specifications
+
+The sniffer **must** match these parameters exactly.
+
+| Parameter        | Value              |
+| ---------------- | ------------------ |
+| Radio Chip       | SX1262             |
+| Frequency        | **915.000 MHz**    |
+| Modulation       | LoRa               |
+| Bandwidth        | **125 kHz**        |
+| Spreading Factor | **SF8**            |
+| Coding Rate      | **4/5**            |
+| Preamble Length  | 8 symbols          |
+| Sync Word        | 0x12 (Public LoRa) |
+| CRC              | Enabled            |
+| IQ Inversion     | Disabled           |
+| Output Power     | 14 dBm (default)   |
+
+---
+
+## Important Notes for Sniffer Operators
+
+### 1. Frequency
+
+Ensure your sniffer JSON or configuration file contains:
+
+```
+"freq": 915000000
+```
+
+If using SX130x HAL:
+
+```
+915000000
+```
+
+No offset. No channel hopping.
+
+---
+
+### 2. Spreading Factor
+
+Must be:
+
+```
+SF8
+```
+
+If the sniffer is set to multi-SF mode, confirm that SF8 is enabled.
+
+---
+
+### 3. Bandwidth
+
+```
+125000 Hz
+```
+
+Not 250 kHz. Not 500 kHz.
+
+---
+
+### 4. Coding Rate
+
+```
+4/5
+```
+
+Some interfaces represent this as:
+
+```
+CR = 1
+```
+
+---
+
+### 5. Sync Word
+
+If your sniffer filters on sync word:
+
+```
+0x12
+```
+
+This is the public LoRa sync word (not LoRaWAN private).
+
+---
+
+## Expected Packet Behavior
+
+The transmitter:
+
+* Sends a short ASCII payload
+* Repeats at a fixed interval
+* Does not use LoRaWAN
+* Does not use encryption
+* Does not use MAC layer framing
+
+Sniffer output should display:
+
+* RSSI
+* SNR
+* SF8
+* BW125
+* Payload length matching transmitter
+
+---
+
+## Confirming Correct Alignment
+
+A properly aligned sniffer will show:
+
+* Stable RSSI
+* Correct SF detection (SF8)
+* Clean CRC pass
+* No excessive packet loss at short range
+
+If you see:
+
+* No packets → Check frequency mismatch first.
+* Packets but CRC fail → Check bandwidth mismatch.
+* Packets only intermittently → Check spreading factor.
+
+---
+
+## SX1262 SPI Mapping (T-Beam SUPREME)
+
+For reference, the radio is connected as follows:
+
+| Signal | ESP32-S3 Pin |
+| ------ | ------------ |
+| SCK    | 12           |
+| MISO   | 13           |
+| MOSI   | 11           |
+| CS     | 10           |
+| RESET  | 5            |
+| BUSY   | 4            |
+| DIO1   | 1            |
+
+These match the board’s hardware routing.
+
+---
+
+## Build & Flash
+
+### PlatformIO
+
+1. Open project folder
+2. Select correct environment
+3. Compile
+4. Upload via USB-C
+5. Monitor serial output
+
+### Arduino IDE
+
+* Board: ESP32S3 Dev Module
+* Flash: 8MB
+* PSRAM: QSPI
+* Upload speed: 921600
+* USB Mode: CDC and JTAG
+
+---
+
+## Purpose of This Exercise
+
+This exercise verifies:
+
+* SPI communication with SX1262
+* Radio configuration correctness
+* Antenna functionality
+* Sniffer alignment
+* Baseline RF performance
+
+It is intended as the foundational RF validation step before:
+
+* Reticulum interface integration
+* microReticulum radio abstraction
+* LoRa time-synchronized experiments
+* Multi-node field testing
+
+---
+
+## If You Cannot See Packets
+
+Work through this checklist:
+
+1. Confirm antenna attached.
+2. Confirm sniffer at 915 MHz.
+3. Confirm SF8.
+4. Confirm BW125.
+5. Reduce distance to < 2 meters.
+6. Increase TX power to 17–20 dBm for testing.
+7. Confirm no regional regulatory lock mismatch.
+
+---
+
+## Relationship to `main.cpp`
+
+This README corresponds to the current exercise implementation in:
+
+```
+main.cpp
+```
+
+See source for definitive parameter values 
+
+If you modify radio parameters in code, update this README accordingly.
+
+

exercises/01_lora_ascii_pingpong/platformio.ini

@@ -0,0 +1,57 @@
+; 20260212 ChatGPT
+; $Id$
+; $HeadURL$
+
+[platformio]
+default_envs = amy
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+monitor_speed = 115200
+lib_deps =
+  jgromes/RadioLib@^6.6.0
+
+; Common build flags (pins from Meshtastic tbeam-s3-core variant.h)
+build_flags =
+  -D LORA_CS=10
+  -D LORA_MOSI=11
+  -D LORA_SCK=12
+  -D LORA_MISO=13
+  -D LORA_RESET=5
+  -D LORA_DIO1=1
+  -D LORA_BUSY=4
+  -D LORA_TCXO_VOLTAGE=1.8
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+
+[env:amy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"Amy\"
+
+[env:bob]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"Bob\"
+
+[env:cy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"Cy\"
+
+[env:dan]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"Dan\"
+
+[env:ed]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"Ed\"

exercises/01_lora_ascii_pingpong/src/main.cpp

@@ -0,0 +1,151 @@
+// 20260212 ChatGPT
+// $Id$
+// $HeadURL$
+
+#include <Arduino.h>
+#include <SPI.h>
+#include <RadioLib.h>
+
+// --- Compile-time label ---
+#ifndef NODE_LABEL
+#define NODE_LABEL "?"
+#endif
+#ifndef UNIT_NAME
+  #define UNIT_NAME "UNNAMED"
+#endif
+
+// --- Pins injected via platformio.ini build_flags ---
+#ifndef LORA_CS
+#error "LORA_CS not defined"
+#endif
+#ifndef LORA_DIO1
+#error "LORA_DIO1 not defined"
+#endif
+#ifndef LORA_RESET
+#error "LORA_RESET not defined"
+#endif
+#ifndef LORA_BUSY
+#error "LORA_BUSY not defined"
+#endif
+
+// SX1262 on T-Beam Supreme (tbeam-s3-core pinout)
+SX1262 radio = new Module(LORA_CS, LORA_DIO1, LORA_RESET, LORA_BUSY);
+
+static volatile bool g_rx_flag = false;
+
+
+static void onDio1Rise() {
+  g_rx_flag = true;
+}
+
+static void print_config() {
+  Serial.printf("Node=%s\n", NODE_LABEL);
+  Serial.printf("Pins: CS=%d DIO1=%d RST=%d BUSY=%d SCK=%d MISO=%d MOSI=%d\r\n",
+                (int)LORA_CS, (int)LORA_DIO1, (int)LORA_RESET, (int)LORA_BUSY,
+                (int)LORA_SCK, (int)LORA_MISO, (int)LORA_MOSI);
+  Serial.printf("LoRa: freq=915.0 BW=125 SF=7 CR=5 txp=14\r\n");
+}
+
+void setup() {
+  Serial.begin(115200);
+  delay(250);
+  Serial.println();
+  Serial.println("Exercise 01: LoRa ASCII ping-pong (serial only)");
+
+  // Ensure SPI pins match the variant
+  SPI.begin(LORA_SCK, LORA_MISO, LORA_MOSI, LORA_CS);
+
+  int state = radio.begin(915.0 /* MHz */, 125.0 /* kHz */, 7 /* SF */, 5 /* CR */, 0x12 /* sync */, 14 /* dBm */);
+  if (state != RADIOLIB_ERR_NONE) {
+    Serial.printf("ERROR: radio.begin failed, code=%d\r\n", state);
+    while (true) delay(1000);
+  }
+
+  // Match Meshtastic-like wiring assumptions for SX1262 modules:
+  // - DIO2 used as RF switch
+  // - TCXO at 1.8V
+  //OLD radio.setDio2AsRfSwitch(true);
+  //OLD radio.setTcxoVoltage((float)LORA_TCXO_VOLTAGE);
+  // below is replacement for above 2 lines:
+
+  //maybe_setDio2AsRfSwitch(radio, true);
+  //maybe_setTcxoVoltage(radio, (float)LORA_TCXO_VOLTAGE);
+
+  // end of replacement
+  
+  // Set up RX interrupt
+  radio.setDio1Action(onDio1Rise);
+
+  // Start receiving
+  state = radio.startReceive();
+  if (state != RADIOLIB_ERR_NONE) {
+    Serial.printf("ERROR: startReceive failed, code=%d\r\n", state);
+    while (true) delay(1000);
+  }
+
+  print_config();
+}
+
+void loop() {
+  // Periodic TX (with a label-based offset to reduce collisions)
+  static uint32_t next_tx_ms = 0;
+  static uint32_t iter = 0;
+  uint32_t now = millis();
+
+  if (next_tx_ms == 0) {
+    // Offset A and B so they don't always collide
+    uint32_t offset = (NODE_LABEL[0] == 'A') ? 500 : 1500;
+    next_tx_ms = now + offset;
+  }
+
+  if ((int32_t)(now - next_tx_ms) >= 0) {
+    next_tx_ms = now + 2000; // 2 seconds for this smoke test
+
+    // String msg = String("I am ") + NODE_LABEL + " iter=" + String(iter++);
+    String msg = String("") + NODE_LABEL + " says hi. iter=" + String(iter++);
+    Serial.printf("TX: %s\r\n", msg.c_str());
+
+    //int tx = radio.transmit(msg);
+    //if (tx != RADIOLIB_ERR_NONE) {
+    //  Serial.printf("TX ERROR code=%d\r\n", tx);
+    // }
+
+    // After transmit, resume RX
+    //radio.startReceive();
+    // DIO1 triggers on TX-done as well as RX-done.
+    // If left armed, TX completion looks like RX.
+    g_rx_flag = false;
+    radio.clearDio1Action();
+    
+    int tx = radio.transmit(msg);
+    if (tx != RADIOLIB_ERR_NONE) {
+      Serial.printf("TX ERROR code=%d\r\n", tx);
+    }
+    
+    // Re-arm RX interrupt and resume RX
+    g_rx_flag = false;
+    radio.setDio1Action(onDio1Rise);
+    radio.startReceive();
+
+  }
+
+  // RX handling
+  if (g_rx_flag) {
+    g_rx_flag = false;
+
+    String rx;
+    int state = radio.readData(rx);
+    if (state == RADIOLIB_ERR_NONE) {
+      Serial.printf("RX: %s | RSSI=%.1f SNR=%.1f\r\n",
+                    rx.c_str(), radio.getRSSI(), radio.getSNR());
+    } else {
+      Serial.printf("RX ERROR code=%d\r\n", state);
+    }
+
+    // Keep receiving
+    radio.startReceive();
+  }
+
+  delay(5);
+}
+

exercises/02_oled_display/README.md

@@ -0,0 +1,55 @@
+## Exercise 02: OLED Display
+
+This exercise demonstrates multiple OLED rendering patterns on the LilyGO T-Beam Supreme (SH1106).
+
+The firmware runs 3 demos in sequence, then shows a restart banner and repeats forever.
+
+## Demo Sequence
+
+### Demo 1: Scrolling Text
+- Shows `Hello #<n>` lines.
+- New lines are added below prior lines.
+- Up to 5 lines are visible; old lines roll off the top.
+
+### Demo 2: Fill Then Erase
+- Displays `Count 1` through `Count 10`.
+- Shows a short `Clearing screen...` message.
+- Erases the OLED to demonstrate explicit clear behavior.
+
+### Demo 3: Multi-Page Rotation
+- Rotates through 3 distinct text pages.
+- Each page has different content/layout to demonstrate refresh transitions.
+- Includes a changing packet counter field on one page.
+
+### Restart Banner
+- Shows `Restarting 3 demos` for 5 seconds.
+- Sequence restarts at Demo 1.
+
+## Expected Serial Output
+Serial output (115200) prints phase changes, for example:
+- `Demo 1/3: scrolling Hello #`
+- `Demo 2/3: clear screen after 10`
+- `Demo 3/3: three-page rotation`
+- `Restarting 3 demos`
+
+### Build
+From this directory:
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e node_a
+```
+
+### Upload
+Set your USB port:
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e node_a -t upload --upload-port /dev/ttyACM0
+```
+
+### Serial Monitor
+
+```bash
+screen /dev/ttyACM0 115200
+```

exercises/02_oled_display/platformio.ini

@@ -0,0 +1,32 @@
+; 20260213 ChatGPT
+; $Id$
+; $HeadURL$
+
+[platformio]
+default_envs = node_a
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+monitor_speed = 115200
+lib_deps =
+  olikraus/U8g2@^2.36.4
+
+; Common build flags (pins from Meshtastic tbeam-s3-core variant.h)
+build_flags =
+  -D OLED_SDA=17
+  -D OLED_SCL=18
+  -D OLED_ADDR=0x3C
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+
+[env:node_a]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"A\"
+
+[env:node_b]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"B\"

exercises/02_oled_display/src/main.cpp

@@ -0,0 +1,162 @@
+// 20260213 ChatGPT
+// $Id$
+// $HeadURL$
+
+#include <Arduino.h>
+#include <Wire.h>
+#include <U8g2lib.h>
+
+#ifndef OLED_SDA
+#define OLED_SDA 17
+#endif
+
+#ifndef OLED_SCL
+#define OLED_SCL 18
+#endif
+
+#ifndef OLED_ADDR
+#define OLED_ADDR 0x3C
+#endif
+
+// LilyGO T-Beam Supreme uses SH1106 OLED on I2C.
+U8G2_SH1106_128X64_NONAME_F_HW_I2C oled(U8G2_R0, /* reset=*/U8X8_PIN_NONE);
+
+static const uint8_t kMaxLines = 5;
+static String g_lines[kMaxLines];
+static uint32_t g_iteration = 1;
+static uint32_t g_pageCounter = 1;
+
+static void addLine(const String& line) {
+  for (uint8_t i = 0; i < kMaxLines - 1; ++i) {
+    g_lines[i] = g_lines[i + 1];
+  }
+  g_lines[kMaxLines - 1] = line;
+}
+
+static void drawLines() {
+  oled.clearBuffer();
+  oled.setFont(u8g2_font_6x10_tf);
+
+  const int yStart = 12;
+  const int yStep = 12;
+  for (uint8_t i = 0; i < kMaxLines; ++i) {
+    if (g_lines[i].length() == 0) {
+      continue;
+    }
+    oled.drawUTF8(0, yStart + (i * yStep), g_lines[i].c_str());
+  }
+  oled.sendBuffer();
+}
+
+static void clearLines() {
+  for (uint8_t i = 0; i < kMaxLines; ++i) {
+    g_lines[i] = "";
+  }
+}
+
+static void showCentered(const char* line1, const char* line2 = nullptr, const char* line3 = nullptr) {
+  oled.clearBuffer();
+  oled.setFont(u8g2_font_6x10_tf);
+
+  if (line1) oled.drawUTF8(0, 16, line1);
+  if (line2) oled.drawUTF8(0, 32, line2);
+  if (line3) oled.drawUTF8(0, 48, line3);
+
+  oled.sendBuffer();
+}
+
+static void demo1_scrollingHello() {
+  Serial.println("Demo 1/3: scrolling Hello #");
+  clearLines();
+  for (uint8_t i = 0; i < 10; ++i) {
+    String line = "Hello #" + String(g_iteration++);
+    addLine(line);
+    drawLines();
+    delay(1000);
+  }
+}
+
+static void demo2_clearAfterTen() {
+  Serial.println("Demo 2/3: clear screen after 10");
+  clearLines();
+  for (uint8_t i = 1; i <= 10; ++i) {
+    String line = "Count " + String(i);
+    addLine(line);
+    drawLines();
+    delay(500);
+  }
+
+  showCentered("Demo 2", "Clearing screen...");
+  delay(1000);
+  oled.clearDisplay();
+  oled.sendBuffer();
+  delay(1000);
+}
+
+static void drawPage(uint8_t page) {
+  oled.clearBuffer();
+  oled.setFont(u8g2_font_6x10_tf);
+
+  if (page == 0) {
+    oled.drawUTF8(0, 12, "Demo 3 - Page 1/3");
+    oled.drawUTF8(0, 28, "GPS: 37.7749 N");
+    oled.drawUTF8(0, 40, "LON: 122.4194 W");
+    oled.drawUTF8(0, 56, "Fix: 3D");
+  } else if (page == 1) {
+    oled.drawUTF8(0, 12, "Demo 3 - Page 2/3");
+    oled.drawUTF8(0, 28, "LoRa RSSI: -92 dBm");
+    oled.drawUTF8(0, 40, "LoRa SNR:  +8.5 dB");
+    oled.drawUTF8(0, 56, "Pkts: " );
+    oled.setCursor(38, 56);
+    oled.print(g_pageCounter++);
+  } else {
+    oled.drawUTF8(0, 12, "Demo 3 - Page 3/3");
+    oled.drawUTF8(0, 28, "Node: TBM-SUPREME");
+    oled.drawUTF8(0, 40, "Mode: Field Test");
+    oled.drawUTF8(0, 56, "OLED refresh demo");
+  }
+
+  oled.sendBuffer();
+}
+
+static void demo3_threePages() {
+  Serial.println("Demo 3/3: three-page rotation");
+  for (uint8_t round = 0; round < 3; ++round) {
+    drawPage(0);
+    delay(700);
+    drawPage(1);
+    delay(700);
+    drawPage(2);
+    delay(700);
+  }
+}
+
+static void showRestartBanner() {
+  Serial.println("Restarting 3 demos");
+  showCentered("Restarting 3 demos", "Cycle begins again", "in 5 seconds...");
+  delay(5000);
+}
+
+void setup() {
+  Serial.begin(115200);
+  delay(250);
+
+  Wire.begin(OLED_SDA, OLED_SCL);
+  oled.setI2CAddress(OLED_ADDR << 1); // U8g2 expects 8-bit address.
+  oled.begin();
+
+  oled.clearBuffer();
+  oled.setFont(u8g2_font_6x10_tf);
+  oled.drawUTF8(0, 12, "Exercise 02 OLED");
+  oled.sendBuffer();
+
+  Serial.println("Exercise 02: OLED display loop");
+  Serial.printf("OLED SDA=%d SCL=%d ADDR=0x%02X\r\n", OLED_SDA, OLED_SCL, OLED_ADDR);
+}
+
+void loop() {
+  demo1_scrollingHello();
+  demo2_clearAfterTen();
+  demo3_threePages();
+  showRestartBanner();
+}

exercises/04_SD_card/README.md

@@ -0,0 +1,37 @@
+## Exercise 04: SD Card
+
+This exercise loops forever. Each cycle:
+
+1. Prints `Sleeping 10 seconds` and waits 10 seconds.
+2. Detects and mounts the SD card.
+3. Prints card and filesystem info (type/size/used).
+4. Writes `/Exercise_04_test.txt` with:
+   - `This is a test`
+5. Ensures nested directories exist:
+   - `/test/testsub1/testsubsub1`
+6. Writes nested file:
+   - `/test/testsub1/testsubsub1/Exercise_04_test.txt`
+7. If either target file already exists, prints warning, erases it, then recreates it.
+8. Demonstrates permission behavior:
+   - Notes FAT does not provide Unix `chmod/chown`.
+   - Shows access behavior via `FILE_READ` vs `FILE_WRITE` modes.
+
+## Build
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e node_a
+```
+
+## Upload
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e node_a -t upload --upload-port /dev/ttyACM0
+```
+
+## Monitor
+
+```bash
+screen /dev/ttyACM0 115200
+```

exercises/04_SD_card/platformio.ini

@@ -0,0 +1,33 @@
+; 20260213 ChatGPT
+; $Id$
+; $HeadURL$
+
+[platformio]
+default_envs = node_a
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+monitor_speed = 115200
+lib_deps =
+  lewisxhe/XPowersLib@0.3.3
+  Wire
+
+; SD pins based on T-Beam S3 core pin mapping
+build_flags =
+  -I ../../shared/boards
+  -I ../../external/microReticulum_Firmware
+  -D BOARD_MODEL=BOARD_TBEAM_S_V1
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+
+[env:node_a]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"A\"
+
+[env:node_b]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"B\"

exercises/04_SD_card/src/main.cpp

@@ -0,0 +1,228 @@
+// 20260213 ChatGPT
+// $Id$
+// $HeadURL$
+
+#include <Arduino.h>
+#include <FS.h>
+#include <SD.h>
+#include <SPI.h>
+#include "tbeam_supreme_adapter.h"
+
+static SPIClass sdSpiH(HSPI);
+static SPIClass sdSpiF(FSPI);
+static SPIClass* g_sdSpi = nullptr;
+static const char* g_sdBusName = "none";
+static uint32_t g_sdFreq = 0;
+static XPowersLibInterface* g_pmu = nullptr;
+
+static const char* kRootTestFile = "/Exercise_04_test.txt";
+static const char* kNestedDir = "/test/testsub1/testsubsub1";
+static const char* kNestedTestFile = "/test/testsub1/testsubsub1/Exercise_04_test.txt";
+static const char* kPayload = "This is a test";
+
+static bool initPmuForSdPower() {
+  return tbeam_supreme::initPmuForPeripherals(g_pmu, &Serial);
+}
+
+static const char* cardTypeToString(uint8_t type) {
+  switch (type) {
+    case CARD_MMC: return "MMC";
+    case CARD_SD: return "SDSC";
+    case CARD_SDHC: return "SDHC/SDXC";
+    default: return "UNKNOWN";
+  }
+}
+
+static bool tryMountWithBus(SPIClass& bus, const char* busName, uint32_t hz) {
+  SD.end();
+  bus.end();
+  delay(10);
+
+  // Keep inactive devices deselected on shared bus lines.
+  pinMode(tbeam_supreme::sdCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  pinMode(tbeam_supreme::imuCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::imuCs(), HIGH);
+
+  bus.begin(tbeam_supreme::sdSck(), tbeam_supreme::sdMiso(), tbeam_supreme::sdMosi(), tbeam_supreme::sdCs());
+  delay(2);
+
+  Serial.printf("SD: trying bus=%s freq=%lu Hz\r\n", busName, (unsigned long)hz);
+  if (!SD.begin(tbeam_supreme::sdCs(), bus, hz)) {
+    Serial.println("SD: mount failed (possible non-FAT format, power, or bus issue)");
+    return false;
+  }
+
+  uint8_t cardType = SD.cardType();
+  if (cardType == CARD_NONE) {
+    SD.end();
+    return false;
+  }
+
+  g_sdSpi = &bus;
+  g_sdBusName = busName;
+  g_sdFreq = hz;
+  return true;
+}
+
+static bool mountCard() {
+  const uint32_t freqs[] = {400000, 1000000, 4000000, 10000000};
+
+  for (uint8_t i = 0; i < (sizeof(freqs) / sizeof(freqs[0])); ++i) {
+    if (tryMountWithBus(sdSpiH, "HSPI", freqs[i])) {
+      Serial.println("SD: card detected and mounted");
+      return true;
+    }
+  }
+  for (uint8_t i = 0; i < (sizeof(freqs) / sizeof(freqs[0])); ++i) {
+    if (tryMountWithBus(sdSpiF, "FSPI", freqs[i])) {
+      Serial.println("SD: card detected and mounted");
+      return true;
+    }
+  }
+
+  Serial.println("SD: begin() failed on all bus/frequency attempts");
+  Serial.println("    likely card absent, bad format, pin mismatch, or hardware issue");
+  return false;
+}
+
+static void printCardInfo() {
+  uint8_t cardType = SD.cardType();
+  uint64_t cardSizeMB = SD.cardSize() / (1024ULL * 1024ULL);
+  uint64_t totalMB = SD.totalBytes() / (1024ULL * 1024ULL);
+  uint64_t usedMB = SD.usedBytes() / (1024ULL * 1024ULL);
+
+  Serial.printf("SD type: %s\r\n", cardTypeToString(cardType));
+  Serial.printf("SD size: %llu MB\r\n", cardSizeMB);
+  Serial.printf("FS total: %llu MB\r\n", totalMB);
+  Serial.printf("FS used : %llu MB\r\n", usedMB);
+  Serial.printf("SPI bus: %s @ %lu Hz\r\n", g_sdBusName, (unsigned long)g_sdFreq);
+}
+
+static bool ensureDirRecursive(const char* path) {
+  String full(path);
+  if (!full.startsWith("/")) {
+    full = "/" + full;
+  }
+
+  int start = 1;
+  while (start > 0 && start < (int)full.length()) {
+    int slash = full.indexOf('/', start);
+    String partial = (slash < 0) ? full : full.substring(0, slash);
+
+    if (!SD.exists(partial.c_str())) {
+      Serial.printf("Creating directory: %s\r\n", partial.c_str());
+      if (!SD.mkdir(partial.c_str())) {
+        Serial.printf("ERROR: mkdir failed for %s\r\n", partial.c_str());
+        return false;
+      }
+    }
+
+    if (slash < 0) {
+      break;
+    }
+    start = slash + 1;
+  }
+
+  return true;
+}
+
+static bool rewriteFile(const char* path, const char* payload) {
+  if (SD.exists(path)) {
+    Serial.printf("WARNING: %s exists ... erasing\r\n", path);
+    if (!SD.remove(path)) {
+      Serial.printf("ERROR: failed to erase %s\r\n", path);
+      return false;
+    }
+  }
+
+  File f = SD.open(path, FILE_WRITE);
+  if (!f) {
+    Serial.printf("ERROR: failed to create %s\r\n", path);
+    return false;
+  }
+
+  size_t wrote = f.println(payload);
+  f.close();
+
+  if (wrote == 0) {
+    Serial.printf("ERROR: write failed for %s\r\n", path);
+    return false;
+  }
+
+  Serial.printf("Wrote file: %s\r\n", path);
+  return true;
+}
+
+static void permissionsDemo(const char* path) {
+  Serial.println("Permissions demo:");
+  Serial.println("  SD/FAT does not support Unix permissions (chmod/chown).");
+  Serial.println("  Access control is by open mode (FILE_READ/FILE_WRITE).");
+
+  File r = SD.open(path, FILE_READ);
+  if (!r) {
+    Serial.printf("  Could not open %s as FILE_READ\r\n", path);
+    return;
+  }
+
+  Serial.printf("  FILE_READ open succeeded, size=%u bytes\r\n", (unsigned)r.size());
+  size_t writeInReadMode = r.print("attempt write while opened read-only");
+  if (writeInReadMode == 0) {
+    Serial.println("  As expected, write via FILE_READ handle was blocked.");
+  } else {
+    Serial.printf("  NOTE: write via FILE_READ returned %u (unexpected)\r\n", (unsigned)writeInReadMode);
+  }
+  r.close();
+}
+
+void setup() {
+  Serial.begin(115200);
+  Serial.println("Sleeping for 5 seconds to allow Serial Monitor connection...");
+  delay(5000); // Time to open Serial Monitor after reset
+
+  Serial.println("\r\n==================================================");
+  Serial.println("Exercise 04: SD card test loop");
+  Serial.println("==================================================");
+  Serial.printf("Pins: CS=%d SCK=%d MISO=%d MOSI=%d\r\n",
+                tbeam_supreme::sdCs(), tbeam_supreme::sdSck(),
+                tbeam_supreme::sdMiso(), tbeam_supreme::sdMosi());
+  Serial.printf("PMU I2C: SDA1=%d SCL1=%d\r\n",
+                tbeam_supreme::i2cSda(), tbeam_supreme::i2cScl());
+  Serial.println("Note: SD must be FAT16/FAT32 for Arduino SD library.\r\n");
+
+  initPmuForSdPower();
+}
+
+void loop() {
+  Serial.println("Sleeping 10 seconds");
+  delay(10000);
+
+  if (!mountCard()) {
+    Serial.println("SD step skipped this cycle.\r\n");
+    return;
+  }
+
+  printCardInfo();
+
+  if (!rewriteFile(kRootTestFile, kPayload)) {
+    SD.end();
+    Serial.println("Cycle ended due to root file error.\r\n");
+    return;
+  }
+
+  if (!ensureDirRecursive(kNestedDir)) {
+    SD.end();
+    Serial.println("Cycle ended due to directory creation error.\r\n");
+    return;
+  }
+
+  if (!rewriteFile(kNestedTestFile, kPayload)) {
+    SD.end();
+    Serial.println("Cycle ended due to nested file error.\r\n");
+    return;
+  }
+
+  permissionsDemo(kRootTestFile);
+  SD.end();
+  Serial.println("Cycle complete.\r\n");
+}

exercises/05_SD_Card_Watcher/README.md

@@ -0,0 +1,39 @@
+## Exercise 05: SD Card Watcher
+
+This exercise continuously watches SD card presence and prints state-change events.
+
+Watcher behavior:
+
+1. Initializes PMU and enables SD power rail (AXP2101 BLDO1).
+2. Polls for card changes with debounced state transitions.
+3. Emits events only on change:
+   - `EVENT: card inserted/mounted`
+   - `EVENT: card removed/unavailable`
+   - `EVENT: no card detected`
+4. On mount event, prints card info and runs SD write workflow.
+5. Every 15 seconds while mounted, runs a periodic write/permission check.
+6. Uses fast preferred probe (`HSPI @ 400k`) and occasional full fallback scan.
+
+Files used in this exercise:
+- `/Exercise_05_test.txt`
+- `/test/testsub1/testsubsub1/Exercise_05_test.txt`
+
+## Build
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e node_a
+```
+
+## Upload
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e node_a -t upload --upload-port /dev/ttyACM0
+```
+
+## Monitor
+
+```bash
+screen /dev/ttyACM0 115200
+```

exercises/05_SD_Card_Watcher/platformio.ini

@@ -0,0 +1,33 @@
+; 20260213 ChatGPT
+; $Id$
+; $HeadURL$
+
+[platformio]
+default_envs = node_a
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+monitor_speed = 115200
+lib_deps =
+  lewisxhe/XPowersLib@0.3.3
+  Wire
+
+; SD pins based on T-Beam S3 core pin mapping
+build_flags =
+  -I ../../shared/boards
+  -I ../../external/microReticulum_Firmware
+  -D BOARD_MODEL=BOARD_TBEAM_S_V1
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+
+[env:node_a]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"A\"
+
+[env:node_b]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"B\"

exercises/05_SD_Card_Watcher/src/main.cpp

@@ -0,0 +1,485 @@
+// 20260214 ChatGPT
+// $Id$
+// $HeadURL$
+
+#include <Arduino.h>
+#include <stdarg.h>
+#include <FS.h>
+#include <SD.h>
+#include <SPI.h>
+#include "driver/gpio.h"          // gpio_get_level()
+#include "tbeam_supreme_adapter.h"
+
+// -------------------------
+// Configuration toggles
+// -------------------------
+#define ENABLE_SD_RAIL_CYCLE    1   // Power-cycle AXP2101 BLDO1 (SD rail) at boot.
+#define ENABLE_PIN_DUMPS        1   // Log SPI pin logic levels at key points (NON-INTRUSIVE).
+#define STARTUP_SERIAL_DELAY_MS 5000
+
+// -------------------------
+// Globals
+// -------------------------
+static SPIClass sdSpiH(HSPI);
+static SPIClass sdSpiF(FSPI);
+static SPIClass* g_sdSpi = nullptr;
+static const char* g_sdBusName = "none";
+static uint32_t g_sdFreq = 0;
+static XPowersLibInterface* g_pmu = nullptr;
+
+static const char* kRootTestFile   = "/Exercise_05_test.txt";
+static const char* kNestedDir      = "/test/testsub1/testsubsub1";
+static const char* kNestedTestFile = "/test/testsub1/testsubsub1/Exercise_05_test.txt";
+static const char* kPayload        = "This is a test";
+
+enum class WatchState : uint8_t {
+  UNKNOWN = 0,
+  ABSENT,
+  MOUNTED
+};
+
+static WatchState g_watchState = WatchState::UNKNOWN;
+static uint8_t g_presentVotes = 0;
+static uint8_t g_absentVotes = 0;
+static uint32_t g_lastPollMs = 0;
+static uint32_t g_lastFullScanMs = 0;
+static uint32_t g_lastPeriodicActionMs = 0;
+
+static const uint32_t kPollIntervalAbsentMs  = 1000;
+static const uint32_t kPollIntervalMountedMs = 2000;
+static const uint32_t kFullScanIntervalMs    = 10000;
+static const uint32_t kPeriodicActionMs      = 15000;
+
+static const uint8_t  kVotesToPresent = 2;
+static const uint8_t  kVotesToAbsent  = 5;     // More votes needed to declare absent to prevent false removes.
+static const uint32_t kStartupWarmupMs = 1500; // Allow PMU and SD rail to stabilize.
+
+static uint32_t g_logSeq = 0;
+
+// -------------------------
+// Logging helpers
+// -------------------------
+static void logf(const char* fmt, ...) {
+  char msg[192];
+  va_list args;
+  va_start(args, fmt);
+  vsnprintf(msg, sizeof(msg), fmt, args);
+  va_end(args);
+  Serial.printf("[%10lu][%06lu] %s\r\n",
+                (unsigned long)millis(),
+                (unsigned long)g_logSeq++,
+                msg);
+}
+
+static void dumpPmu(const char* tag, XPowersLibInterface* pmu) {
+  if (!pmu) {
+    logf("PMU(%s): pmu=null", tag);
+    return;
+  }
+
+  bool bldo1 = pmu->isPowerChannelEnable(XPOWERS_BLDO1);
+  int vbus = pmu->getVbusVoltage();
+  int batt = pmu->getBattVoltage();
+
+  logf("PMU(%s): BLDO1(SD)=%s  VBUS=%dmV  VBAT=%dmV",
+       tag, bldo1 ? "ON" : "OFF", vbus, batt);
+}
+
+// IMPORTANT: this function MUST NOT modify pin modes (regression cause).
+static void dumpSdPins(const char* tag) {
+#if ENABLE_PIN_DUMPS
+  const gpio_num_t CS   = (gpio_num_t)tbeam_supreme::sdCs();
+  const gpio_num_t SCK  = (gpio_num_t)tbeam_supreme::sdSck();
+  const gpio_num_t MISO = (gpio_num_t)tbeam_supreme::sdMiso();
+  const gpio_num_t MOSI = (gpio_num_t)tbeam_supreme::sdMosi();
+
+  int cs   = gpio_get_level(CS);
+  int sck  = gpio_get_level(SCK);
+  int miso = gpio_get_level(MISO);
+  int mosi = gpio_get_level(MOSI);
+
+  logf("PINS(%s): CS=%d SCK=%d MISO=%d MOSI=%d", tag, cs, sck, miso, mosi);
+#else
+  (void)tag;
+#endif
+}
+
+// -------------------------
+// Power + bus conditioning
+// -------------------------
+static void forceSpiDeselected() {
+  pinMode(tbeam_supreme::sdCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+
+  pinMode(tbeam_supreme::imuCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::imuCs(), HIGH);
+}
+
+static bool initPmuForSdPower() {
+  bool ok = tbeam_supreme::initPmuForPeripherals(g_pmu, &Serial);
+  if (!ok) {
+    logf("ERROR: PMU init failed");
+    return false;
+  }
+
+  logf("PMU adapter: AXP2101 ready, BLDO1(SD)=%s",
+       g_pmu && g_pmu->isPowerChannelEnable(XPOWERS_BLDO1) ? "ON" : "OFF");
+  return true;
+}
+
+static void cycleSdRail(XPowersLibInterface* pmu,
+                        uint32_t off_ms = 250,
+                        uint32_t on_settle_ms = 600) {
+#if ENABLE_SD_RAIL_CYCLE
+  if (!pmu) {
+    logf("SD rail cycle skipped: pmu=null");
+    return;
+  }
+
+  dumpPmu("pre-sd-cycle", pmu);
+
+  // Ensure the card is NOT selected while power is unstable.
+  forceSpiDeselected();
+  dumpSdPins("pre-sd-cycle");
+
+  pmu->disablePowerOutput(XPOWERS_BLDO1);
+  delay(off_ms);
+
+  pmu->setPowerChannelVoltage(XPOWERS_BLDO1, 3300);
+  pmu->enablePowerOutput(XPOWERS_BLDO1);
+  delay(on_settle_ms);
+
+  dumpPmu("post-sd-cycle", pmu);
+  dumpSdPins("post-sd-cycle");
+#else
+  (void)pmu; (void)off_ms; (void)on_settle_ms;
+#endif
+}
+
+// -------------------------
+// SD helpers
+// -------------------------
+static const char* cardTypeToString(uint8_t type) {
+  switch (type) {
+    case CARD_MMC:  return "MMC";
+    case CARD_SD:   return "SDSC";
+    case CARD_SDHC: return "SDHC/SDXC";
+    default:        return "UNKNOWN";
+  }
+}
+
+static bool tryMountWithBus(SPIClass& bus, const char* busName, uint32_t hz, bool verbose) {
+  SD.end();
+  bus.end();
+  delay(10);
+
+  forceSpiDeselected();
+
+  bus.begin(tbeam_supreme::sdSck(), tbeam_supreme::sdMiso(), tbeam_supreme::sdMosi(), tbeam_supreme::sdCs());
+
+  // SD SPI "idle clocks" ritual: CS HIGH + >= 74 clocks with MOSI high (0xFF).
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  delay(2);
+  for (int i = 0; i < 10; i++) {
+    bus.transfer(0xFF); // 80 clocks total
+  }
+  delay(2);
+
+  dumpSdPins("after-idle-clocks");
+
+  if (verbose) {
+    logf("SD: trying bus=%s freq=%lu Hz", busName, (unsigned long)hz);
+  }
+
+  if (!SD.begin(tbeam_supreme::sdCs(), bus, hz)) {
+    if (verbose) logf("SD: mount failed (possible non-FAT format, power, or bus issue)");
+    return false;
+  }
+
+  uint8_t cardType = SD.cardType();
+  if (cardType == CARD_NONE) {
+    SD.end();
+    return false;
+  }
+
+  g_sdSpi = &bus;
+  g_sdBusName = busName;
+  g_sdFreq = hz;
+  return true;
+}
+
+static bool mountPreferred(bool verbose) {
+  return tryMountWithBus(sdSpiH, "HSPI", 400000, verbose);
+}
+
+static bool mountCardFullScan() {
+  const uint32_t freqs[] = {400000, 1000000, 4000000, 10000000};
+
+  for (uint8_t i = 0; i < (sizeof(freqs) / sizeof(freqs[0])); ++i) {
+    if (tryMountWithBus(sdSpiH, "HSPI", freqs[i], true)) {
+      logf("SD: card detected and mounted");
+      return true;
+    }
+  }
+  for (uint8_t i = 0; i < (sizeof(freqs) / sizeof(freqs[0])); ++i) {
+    if (tryMountWithBus(sdSpiF, "FSPI", freqs[i], true)) {
+      logf("SD: card detected and mounted");
+      return true;
+    }
+  }
+
+  logf("SD: begin() failed on all bus/frequency attempts");
+  logf("    likely card absent, bad format, pin mismatch, or hardware issue");
+  return false;
+}
+
+static void printCardInfo() {
+  uint8_t cardType = SD.cardType();
+  uint64_t cardSizeMB = SD.cardSize() / (1024ULL * 1024ULL);
+  uint64_t totalMB    = SD.totalBytes() / (1024ULL * 1024ULL);
+  uint64_t usedMB     = SD.usedBytes() / (1024ULL * 1024ULL);
+
+  logf("SD type: %s", cardTypeToString(cardType));
+  logf("SD size: %llu MB", cardSizeMB);
+  logf("FS total: %llu MB", totalMB);
+  logf("FS used : %llu MB", usedMB);
+  logf("SPI bus: %s @ %lu Hz", g_sdBusName, (unsigned long)g_sdFreq);
+}
+
+static bool ensureDirRecursive(const char* path) {
+  String full(path);
+  if (!full.startsWith("/")) full = "/" + full;
+
+  int start = 1;
+  while (start > 0 && start < (int)full.length()) {
+    int slash = full.indexOf('/', start);
+    String partial = (slash < 0) ? full : full.substring(0, slash);
+
+    if (!SD.exists(partial.c_str())) {
+      logf("Creating directory: %s", partial.c_str());
+      if (!SD.mkdir(partial.c_str())) {
+        logf("ERROR: mkdir failed for %s", partial.c_str());
+        return false;
+      }
+    }
+
+    if (slash < 0) break;
+    start = slash + 1;
+  }
+  return true;
+}
+
+static bool rewriteFile(const char* path, const char* payload) {
+  if (SD.exists(path)) {
+    logf("WARNING: %s exists ... erasing", path);
+    if (!SD.remove(path)) {
+      logf("ERROR: failed to erase %s", path);
+      return false;
+    }
+  }
+
+  File f = SD.open(path, FILE_WRITE);
+  if (!f) {
+    logf("ERROR: failed to create %s", path);
+    return false;
+  }
+
+  size_t wrote = f.println(payload);
+  f.close();
+
+  if (wrote == 0) {
+    logf("ERROR: write failed for %s", path);
+    return false;
+  }
+
+  logf("Wrote file: %s", path);
+  return true;
+}
+
+static void permissionsDemo(const char* path) {
+  logf("Permissions demo:");
+  logf("  SD/FAT does not support Unix permissions (chmod/chown).");
+  logf("  Access control is by open mode (FILE_READ/FILE_WRITE).");
+
+  File r = SD.open(path, FILE_READ);
+  if (!r) {
+    logf("  Could not open %s as FILE_READ", path);
+    return;
+  }
+
+  logf("  FILE_READ open succeeded, size=%u bytes", (unsigned)r.size());
+  size_t writeInReadMode = r.print("attempt write while opened read-only");
+  if (writeInReadMode == 0) {
+    logf("  As expected, write via FILE_READ handle was blocked.");
+  } else {
+    logf("  NOTE: write via FILE_READ returned %u (unexpected)", (unsigned)writeInReadMode);
+  }
+  r.close();
+}
+
+static bool verifyMountedCard() {
+  File root = SD.open("/", FILE_READ);
+  if (!root) return false;
+  root.close();
+  return true;
+}
+
+static void runCardWorkflow() {
+  printCardInfo();
+
+  if (!rewriteFile(kRootTestFile, kPayload)) {
+    logf("Watcher action: root file write failed");
+    return;
+  }
+  if (!ensureDirRecursive(kNestedDir)) {
+    logf("Watcher action: directory creation failed");
+    return;
+  }
+  if (!rewriteFile(kNestedTestFile, kPayload)) {
+    logf("Watcher action: nested file write failed");
+    return;
+  }
+
+  permissionsDemo(kRootTestFile);
+}
+
+// -------------------------
+// Watcher state transitions
+// -------------------------
+static void setStateMounted() {
+  if (g_watchState != WatchState::MOUNTED) {
+    logf("EVENT: card inserted/mounted");
+    runCardWorkflow();
+    g_lastPeriodicActionMs = millis();
+  }
+  g_watchState = WatchState::MOUNTED;
+}
+
+static void setStateAbsent() {
+  if (g_watchState == WatchState::MOUNTED) {
+    logf("EVENT: card removed/unavailable");
+  } else if (g_watchState != WatchState::ABSENT) {
+    logf("EVENT: no card detected");
+  }
+  SD.end();
+  g_watchState = WatchState::ABSENT;
+}
+
+// -------------------------
+// Arduino entry points
+// -------------------------
+void setup() {
+  Serial.begin(115200);
+  Serial.println("[WATCHER: startup]");
+
+  // De-select SPI devices immediately.
+  forceSpiDeselected();
+  dumpSdPins("very-early");
+
+  logf("Sleeping for %lu ms to allow Serial Monitor connection...", (unsigned long)STARTUP_SERIAL_DELAY_MS);
+  delay(STARTUP_SERIAL_DELAY_MS);
+
+  Serial.println();
+  Serial.println("==================================================");
+  Serial.println("Exercise 05: SD Card Watcher");
+  Serial.println("==================================================");
+  Serial.printf("Pins: CS=%d SCK=%d MISO=%d MOSI=%d\r\n",
+                tbeam_supreme::sdCs(), tbeam_supreme::sdSck(),
+                tbeam_supreme::sdMiso(), tbeam_supreme::sdMosi());
+  Serial.printf("PMU I2C: SDA1=%d SCL1=%d\r\n",
+                tbeam_supreme::i2cSda(), tbeam_supreme::i2cScl());
+  Serial.println("Note: SD must be FAT16/FAT32 for Arduino SD library.");
+  Serial.println();
+
+  initPmuForSdPower();
+  dumpPmu("post-pmu-init", g_pmu);
+
+  // Software equivalent of "remove/insert card".
+  cycleSdRail(g_pmu);
+
+  logf("Watcher: waiting %lu ms for SD rail/card stabilization", (unsigned long)kStartupWarmupMs);
+  delay(kStartupWarmupMs);
+
+  dumpSdPins("pre-warmup-mount");
+
+  bool warmMounted = false;
+  for (uint8_t i = 0; i < 3; ++i) {
+    if (mountPreferred(false)) {
+      warmMounted = true;
+      break;
+    }
+    delay(200);
+  }
+
+  if (warmMounted) {
+    logf("Watcher: startup warmup mount succeeded");
+    setStateMounted();
+  } else {
+    logf("Watcher: startup warmup did not mount card");
+    setStateAbsent();
+  }
+}
+
+void loop() {
+  const uint32_t now = millis();
+  const uint32_t pollInterval =
+      (g_watchState == WatchState::MOUNTED) ? kPollIntervalMountedMs : kPollIntervalAbsentMs;
+
+  if ((uint32_t)(now - g_lastPollMs) < pollInterval) {
+    delay(10);
+    return;
+  }
+  g_lastPollMs = now;
+
+  if (g_watchState == WatchState::MOUNTED) {
+    if (verifyMountedCard()) {
+      if ((uint32_t)(now - g_lastPeriodicActionMs) >= kPeriodicActionMs) {
+        logf("Watcher: periodic mounted check action");
+        runCardWorkflow();
+        g_lastPeriodicActionMs = now;
+      }
+      g_presentVotes = 0;
+      g_absentVotes  = 0;
+      return;
+    }
+
+    // One immediate remount attempt prevents false removes on transient SPI errors.
+    if (mountPreferred(false) && verifyMountedCard()) {
+      g_presentVotes = 0;
+      g_absentVotes  = 0;
+      return;
+    }
+
+    g_absentVotes++;
+    g_presentVotes = 0;
+    if (g_absentVotes >= kVotesToAbsent) {
+      setStateAbsent();
+      g_absentVotes = 0;
+    }
+    return;
+  }
+
+  // ABSENT/UNKNOWN state
+  bool mounted = mountPreferred(false);
+  if (!mounted && (uint32_t)(now - g_lastFullScanMs) >= kFullScanIntervalMs) {
+    g_lastFullScanMs = now;
+    logf("Watcher: preferred probe failed, running full scan");
+    mounted = mountCardFullScan();
+  }
+
+  if (mounted) {
+    g_presentVotes++;
+    g_absentVotes = 0;
+    if (g_presentVotes >= kVotesToPresent) {
+      setStateMounted();
+      g_presentVotes = 0;
+    }
+  } else {
+    g_absentVotes++;
+    g_presentVotes = 0;
+    if (g_absentVotes >= kVotesToAbsent) {
+      setStateAbsent();
+      g_absentVotes = 0;
+    }
+  }
+}

exercises/06_RTC_check/README.md

@@ -0,0 +1,43 @@
+## Exercise 06: RTC Check (PCF8563)
+
+This exercise validates RTC read/write and power-off persistence on the T-Beam Supreme.
+
+It:
+- Initializes PMU + I2C bus used by RTC.
+- Reads RTC at startup.
+- Prints RTC every 10 seconds.
+- Accepts serial commands:
+  - `show`
+  - `set YYYY-MM-DD HH:MM:SS`
+  - `help`
+
+## Build
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e node_a
+```
+
+## Upload
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e node_a -t upload --upload-port /dev/ttyACM0
+```
+
+## Monitor
+
+```bash
+screen /dev/ttyACM0 115200
+```
+
+## Suggested Persistence Test
+
+1. Set the RTC:
+   - `set 2026-02-14 17:30:00`
+2. Confirm:
+   - `show`
+3. Power off the unit for a few minutes.
+4. Power on and run:
+   - `show`
+5. Compare expected elapsed time vs RTC output.

exercises/06_RTC_check/platformio.ini

@@ -0,0 +1,32 @@
+; 20260214 ChatGPT
+; $Id$
+; $HeadURL$
+
+[platformio]
+default_envs = node_a
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+monitor_speed = 115200
+lib_deps =
+  lewisxhe/XPowersLib@0.3.3
+
+build_flags =
+  -I ../../shared/boards
+  -I ../../external/microReticulum_Firmware
+  -D BOARD_MODEL=BOARD_TBEAM_S_V1
+  -D RTC_I2C_ADDR=0x51
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+
+[env:node_a]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"A\"
+
+[env:node_b]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"B\"

exercises/06_RTC_check/src/main.cpp

@@ -0,0 +1,224 @@
+// 20260214 ChatGPT
+// $Id$
+// $HeadURL$
+
+#include <Arduino.h>
+#include <Wire.h>
+#include "tbeam_supreme_adapter.h"
+
+#ifndef RTC_I2C_ADDR
+#define RTC_I2C_ADDR 0x51
+#endif
+
+static XPowersLibInterface* g_pmu = nullptr;
+static uint32_t g_logSeq = 0;
+static uint32_t g_lastPrintMs = 0;
+static String g_cmdBuf;
+static bool g_lastWasCR = false;
+
+struct RtcDateTime {
+  uint16_t year;
+  uint8_t month;
+  uint8_t day;
+  uint8_t hour;
+  uint8_t minute;
+  uint8_t second;
+  uint8_t weekday;
+};
+
+static uint8_t toBcd(uint8_t v) {
+  return ((v / 10U) << 4U) | (v % 10U);
+}
+
+static uint8_t fromBcd(uint8_t b) {
+  return ((b >> 4U) * 10U) + (b & 0x0FU);
+}
+
+static void logf(const char* fmt, ...) {
+  char msg[196];
+  va_list args;
+  va_start(args, fmt);
+  vsnprintf(msg, sizeof(msg), fmt, args);
+  va_end(args);
+  Serial.printf("[%10lu][%06lu] %s\r\n", (unsigned long)millis(), (unsigned long)g_logSeq++, msg);
+}
+
+static bool initPmuForRtc() {
+  return tbeam_supreme::initPmuForPeripherals(g_pmu, &Serial);
+}
+
+static bool rtcRead(RtcDateTime& out, bool& lowVoltageFlag) {
+  Wire1.beginTransmission(RTC_I2C_ADDR);
+  Wire1.write(0x02); // seconds register
+  if (Wire1.endTransmission(false) != 0) {
+    return false;
+  }
+
+  const uint8_t need = 7;
+  uint8_t got = Wire1.requestFrom((int)RTC_I2C_ADDR, (int)need);
+  if (got != need) {
+    return false;
+  }
+
+  uint8_t sec = Wire1.read();
+  uint8_t min = Wire1.read();
+  uint8_t hour = Wire1.read();
+  uint8_t day = Wire1.read();
+  uint8_t weekday = Wire1.read();
+  uint8_t month = Wire1.read();
+  uint8_t year = Wire1.read();
+
+  lowVoltageFlag = (sec & 0x80U) != 0;
+  out.second = fromBcd(sec & 0x7FU);
+  out.minute = fromBcd(min & 0x7FU);
+  out.hour = fromBcd(hour & 0x3FU);
+  out.day = fromBcd(day & 0x3FU);
+  out.weekday = fromBcd(weekday & 0x07U);
+  out.month = fromBcd(month & 0x1FU);
+  uint8_t yy = fromBcd(year);
+  bool century = (month & 0x80U) != 0;
+  out.year = century ? (1900U + yy) : (2000U + yy);
+
+  return true;
+}
+
+static bool rtcWrite(const RtcDateTime& in) {
+  bool century = in.year < 2000;
+  uint8_t yy = (uint8_t)(in.year % 100);
+  uint8_t monthReg = toBcd(in.month) & 0x1FU;
+  if (century) {
+    monthReg |= 0x80U;
+  }
+
+  Wire1.beginTransmission(RTC_I2C_ADDR);
+  Wire1.write(0x02); // seconds register
+  Wire1.write(toBcd(in.second) & 0x7FU);
+  Wire1.write(toBcd(in.minute) & 0x7FU);
+  Wire1.write(toBcd(in.hour) & 0x3FU);
+  Wire1.write(toBcd(in.day) & 0x3FU);
+  Wire1.write(toBcd(in.weekday) & 0x07U);
+  Wire1.write(monthReg);
+  Wire1.write(toBcd(yy));
+  return Wire1.endTransmission() == 0;
+}
+
+static bool parseSetCommand(const String& line, RtcDateTime& dt) {
+  int y, mo, d, h, mi, s;
+  if (sscanf(line.c_str(), "set %d-%d-%d %d:%d:%d", &y, &mo, &d, &h, &mi, &s) != 6) {
+    return false;
+  }
+
+  if (y < 1900 || y > 2099) return false;
+  if (mo < 1 || mo > 12) return false;
+  if (d < 1 || d > 31) return false;
+  if (h < 0 || h > 23) return false;
+  if (mi < 0 || mi > 59) return false;
+  if (s < 0 || s > 59) return false;
+
+  dt.year = (uint16_t)y;
+  dt.month = (uint8_t)mo;
+  dt.day = (uint8_t)d;
+  dt.hour = (uint8_t)h;
+  dt.minute = (uint8_t)mi;
+  dt.second = (uint8_t)s;
+  dt.weekday = 0; // Not critical for this persistence check.
+  return true;
+}
+
+static void printRtcNow(const char* label) {
+  RtcDateTime now{};
+  bool lowV = false;
+  if (!rtcRead(now, lowV)) {
+    logf("%s: RTC read failed", label);
+    return;
+  }
+  logf("%s: %04u-%02u-%02u %02u:%02u:%02u  weekday=%u%s",
+       label,
+       (unsigned)now.year, (unsigned)now.month, (unsigned)now.day,
+       (unsigned)now.hour, (unsigned)now.minute, (unsigned)now.second,
+       (unsigned)now.weekday,
+       lowV ? "  [LOW_VOLTAGE_FLAG]" : "");
+}
+
+static void handleCommand(const String& raw) {
+  String line = raw;
+  line.trim();
+  if (line.length() == 0) {
+    return;
+  }
+
+  if (line == "help") {
+    logf("Commands:");
+    logf("  show");
+    logf("  set YYYY-MM-DD HH:MM:SS");
+    logf("  help");
+    return;
+  }
+  if (line == "show") {
+    printRtcNow("RTC");
+    return;
+  }
+
+  RtcDateTime dt{};
+  if (parseSetCommand(line, dt)) {
+    if (rtcWrite(dt)) {
+      logf("RTC set succeeded");
+      printRtcNow("RTC");
+    } else {
+      logf("RTC set failed");
+    }
+    return;
+  }
+
+  logf("Unknown command: %s", line.c_str());
+}
+
+void setup() {
+  Serial.begin(115200);
+  Serial.println("Sleeping for 5 seconds to allow Serial Monitor connection...");
+  delay(5000);
+
+  Serial.println("\r\n==================================================");
+  Serial.println("Exercise 06: RTC check (PCF8563)");
+  Serial.println("==================================================");
+  Serial.printf("RTC I2C: SDA1=%d SCL1=%d ADDR=0x%02X\r\n",
+                tbeam_supreme::i2cSda(), tbeam_supreme::i2cScl(), RTC_I2C_ADDR);
+
+  initPmuForRtc();
+
+  logf("Type 'help' for commands.");
+  logf("Power-off persistence test:");
+  logf("  1) set time");
+  logf("  2) power off for a few minutes");
+  logf("  3) power on and run 'show' before any GPS sync");
+  printRtcNow("RTC startup");
+}
+
+void loop() {
+  while (Serial.available() > 0) {
+    char c = (char)Serial.read();
+    if (c == '\r' || c == '\n') {
+      // Handle CR, LF, and CRLF/LFCR cleanly as one line ending.
+      if ((c == '\n' && g_lastWasCR) || (c == '\r' && !g_lastWasCR && g_cmdBuf.length() == 0)) {
+        g_lastWasCR = (c == '\r');
+        continue;
+      }
+      handleCommand(g_cmdBuf);
+      g_cmdBuf = "";
+      g_lastWasCR = (c == '\r');
+    } else {
+      g_lastWasCR = false;
+      g_cmdBuf += c;
+      if (g_cmdBuf.length() > 120) {
+        g_cmdBuf = "";
+        logf("Input line too long, buffer cleared");
+      }
+    }
+  }
+
+  uint32_t nowMs = millis();
+  if ((uint32_t)(nowMs - g_lastPrintMs) >= 10000) {
+    g_lastPrintMs = nowMs;
+    printRtcNow("RTC periodic");
+  }
+}

exercises/07_SD_Startup_Watcher/README.md

@@ -0,0 +1,51 @@
+## Exercise 07: SD Startup Watcher
+
+This exercise is derived from `Exercise 05` and keeps that original exercise intact.
+The focus here is isolating reusable SD startup and hot-insert watcher logic into a library-style structure.
+
+This exercise now has two parts:
+
+1. A reusable SD startup/watcher library in `lib/startup_sd`.
+2. A harness app in `src/main.cpp` that demonstrates how to use that library.
+
+Watcher behavior:
+
+1. Initializes PMU and enables SD power rail (AXP2101 BLDO1).
+2. Polls for card changes with debounced state transitions.
+3. Emits events only on change:
+   - `EVENT: card inserted/mounted`
+   - `EVENT: card removed/unavailable`
+   - `EVENT: no card detected`
+4. On mount event, emits callback status (`SdEvent`) and runs SD write workflow.
+5. Every 15 seconds while mounted, runs a periodic write/permission check.
+6. Uses fast preferred probe (`HSPI @ 400k`) and occasional full fallback scan.
+
+Status callback usage:
+
+- `SdEvent::NO_CARD` -> show "Missing SD card / Please insert card to proceed"
+- `SdEvent::CARD_MOUNTED` -> card ready
+- `SdEvent::CARD_REMOVED` -> card removed, wait for insert
+
+Files used in this exercise:
+- `/Exercise_07_test.txt`
+- `/test/testsub1/testsubsub1/Exercise_07_test.txt`
+
+## Build
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e node_a
+```
+
+## Upload
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e node_a -t upload --upload-port /dev/ttyACM0
+```
+
+## Monitor
+
+```bash
+screen /dev/ttyACM0 115200
+```

exercises/07_SD_Startup_Watcher/lib/startup_sd/StartupSdManager.cpp

@@ -0,0 +1,351 @@
+#include "StartupSdManager.h"
+
+#include <stdarg.h>
+#include "driver/gpio.h"
+
+StartupSdManager::StartupSdManager(Print& serial) : serial_(serial) {}
+
+bool StartupSdManager::begin(const SdWatcherConfig& cfg, SdStatusCallback callback) {
+  cfg_ = cfg;
+  callback_ = callback;
+
+  forceSpiDeselected();
+  dumpSdPins("very-early");
+
+  if (!initPmuForSdPower()) {
+    return false;
+  }
+
+  cycleSdRail();
+  delay(cfg_.startupWarmupMs);
+
+  bool warmMounted = false;
+  for (uint8_t i = 0; i < 3; ++i) {
+    if (mountPreferred(false)) {
+      warmMounted = true;
+      break;
+    }
+    delay(200);
+  }
+
+  if (warmMounted) {
+    setStateMounted();
+  } else {
+    setStateAbsent();
+  }
+  return true;
+}
+
+void StartupSdManager::update() {
+  const uint32_t now = millis();
+  const uint32_t pollInterval =
+      (watchState_ == SdWatchState::MOUNTED) ? cfg_.pollIntervalMountedMs : cfg_.pollIntervalAbsentMs;
+
+  if ((uint32_t)(now - lastPollMs_) < pollInterval) {
+    return;
+  }
+  lastPollMs_ = now;
+
+  if (watchState_ == SdWatchState::MOUNTED) {
+    if (verifyMountedCard()) {
+      presentVotes_ = 0;
+      absentVotes_ = 0;
+      return;
+    }
+
+    if (mountPreferred(false) && verifyMountedCard()) {
+      presentVotes_ = 0;
+      absentVotes_ = 0;
+      return;
+    }
+
+    absentVotes_++;
+    presentVotes_ = 0;
+    if (absentVotes_ >= cfg_.votesToAbsent) {
+      setStateAbsent();
+      absentVotes_ = 0;
+    }
+    return;
+  }
+
+  bool mounted = mountPreferred(false);
+  if (!mounted && (uint32_t)(now - lastFullScanMs_) >= cfg_.fullScanIntervalMs) {
+    lastFullScanMs_ = now;
+    if (cfg_.recoveryRailCycleOnFullScan) {
+      logf("Watcher: recovery rail cycle before full scan");
+      cycleSdRail(cfg_.recoveryRailOffMs, cfg_.recoveryRailOnSettleMs);
+      delay(150);
+    }
+    logf("Watcher: preferred probe failed, running full scan");
+    mounted = mountCardFullScan();
+  }
+
+  if (mounted) {
+    presentVotes_++;
+    absentVotes_ = 0;
+    if (presentVotes_ >= cfg_.votesToPresent) {
+      setStateMounted();
+      presentVotes_ = 0;
+    }
+  } else {
+    absentVotes_++;
+    presentVotes_ = 0;
+    if (absentVotes_ >= cfg_.votesToAbsent) {
+      setStateAbsent();
+      absentVotes_ = 0;
+    }
+  }
+}
+
+bool StartupSdManager::consumeMountedEvent() {
+  bool out = mountedEventPending_;
+  mountedEventPending_ = false;
+  return out;
+}
+
+bool StartupSdManager::consumeRemovedEvent() {
+  bool out = removedEventPending_;
+  removedEventPending_ = false;
+  return out;
+}
+
+void StartupSdManager::logf(const char* fmt, ...) {
+  char msg[196];
+  va_list args;
+  va_start(args, fmt);
+  vsnprintf(msg, sizeof(msg), fmt, args);
+  va_end(args);
+  serial_.printf("[%10lu][%06lu] %s\r\n",
+                 (unsigned long)millis(),
+                 (unsigned long)logSeq_++,
+                 msg);
+}
+
+void StartupSdManager::notify(SdEvent event, const char* message) {
+  if (callback_ != nullptr) {
+    callback_(event, message);
+  }
+}
+
+void StartupSdManager::forceSpiDeselected() {
+  pinMode(tbeam_supreme::sdCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  pinMode(tbeam_supreme::imuCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::imuCs(), HIGH);
+}
+
+void StartupSdManager::dumpSdPins(const char* tag) {
+  if (!cfg_.enablePinDumps) {
+    (void)tag;
+    return;
+  }
+
+  const gpio_num_t cs = (gpio_num_t)tbeam_supreme::sdCs();
+  const gpio_num_t sck = (gpio_num_t)tbeam_supreme::sdSck();
+  const gpio_num_t miso = (gpio_num_t)tbeam_supreme::sdMiso();
+  const gpio_num_t mosi = (gpio_num_t)tbeam_supreme::sdMosi();
+  logf("PINS(%s): CS=%d SCK=%d MISO=%d MOSI=%d",
+       tag, gpio_get_level(cs), gpio_get_level(sck), gpio_get_level(miso), gpio_get_level(mosi));
+}
+
+bool StartupSdManager::initPmuForSdPower() {
+  if (!tbeam_supreme::initPmuForPeripherals(pmu_, &serial_)) {
+    logf("ERROR: PMU init failed");
+    return false;
+  }
+  return true;
+}
+
+void StartupSdManager::cycleSdRail(uint32_t offMs, uint32_t onSettleMs) {
+  if (!cfg_.enableSdRailCycle) {
+    return;
+  }
+  if (!pmu_) {
+    logf("SD rail cycle skipped: pmu=null");
+    return;
+  }
+
+  forceSpiDeselected();
+  pmu_->disablePowerOutput(XPOWERS_BLDO1);
+  delay(offMs);
+  pmu_->setPowerChannelVoltage(XPOWERS_BLDO1, 3300);
+  pmu_->enablePowerOutput(XPOWERS_BLDO1);
+  delay(onSettleMs);
+}
+
+bool StartupSdManager::tryMountWithBus(SPIClass& bus, const char* busName, uint32_t hz, bool verbose) {
+  SD.end();
+  bus.end();
+  delay(10);
+  forceSpiDeselected();
+
+  bus.begin(tbeam_supreme::sdSck(), tbeam_supreme::sdMiso(), tbeam_supreme::sdMosi(), tbeam_supreme::sdCs());
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  delay(2);
+  for (int i = 0; i < 10; i++) {
+    bus.transfer(0xFF);
+  }
+  delay(2);
+
+  if (verbose) {
+    logf("SD: trying bus=%s freq=%lu Hz", busName, (unsigned long)hz);
+  }
+
+  if (!SD.begin(tbeam_supreme::sdCs(), bus, hz)) {
+    if (verbose) {
+      logf("SD: mount failed");
+    }
+    return false;
+  }
+
+  if (SD.cardType() == CARD_NONE) {
+    SD.end();
+    return false;
+  }
+
+  sdSpi_ = &bus;
+  sdBusName_ = busName;
+  sdFreq_ = hz;
+  return true;
+}
+
+bool StartupSdManager::mountPreferred(bool verbose) {
+  return tryMountWithBus(sdSpiH_, "HSPI", 400000, verbose);
+}
+
+bool StartupSdManager::mountCardFullScan() {
+  const uint32_t freqs[] = {400000, 1000000, 4000000, 10000000};
+
+  for (uint8_t i = 0; i < (sizeof(freqs) / sizeof(freqs[0])); ++i) {
+    if (tryMountWithBus(sdSpiH_, "HSPI", freqs[i], true)) {
+      logf("SD: card detected and mounted");
+      return true;
+    }
+  }
+  for (uint8_t i = 0; i < (sizeof(freqs) / sizeof(freqs[0])); ++i) {
+    if (tryMountWithBus(sdSpiF_, "FSPI", freqs[i], true)) {
+      logf("SD: card detected and mounted");
+      return true;
+    }
+  }
+
+  logf("SD: begin() failed on all bus/frequency attempts");
+  return false;
+}
+
+bool StartupSdManager::verifyMountedCard() {
+  File root = SD.open("/", FILE_READ);
+  if (!root) {
+    return false;
+  }
+  root.close();
+  return true;
+}
+
+const char* StartupSdManager::cardTypeToString(uint8_t type) {
+  switch (type) {
+    case CARD_MMC:
+      return "MMC";
+    case CARD_SD:
+      return "SDSC";
+    case CARD_SDHC:
+      return "SDHC/SDXC";
+    default:
+      return "UNKNOWN";
+  }
+}
+
+void StartupSdManager::printCardInfo() {
+  uint8_t cardType = SD.cardType();
+  uint64_t cardSizeMB = SD.cardSize() / (1024ULL * 1024ULL);
+  uint64_t totalMB = SD.totalBytes() / (1024ULL * 1024ULL);
+  uint64_t usedMB = SD.usedBytes() / (1024ULL * 1024ULL);
+
+  logf("SD type: %s", cardTypeToString(cardType));
+  logf("SD size: %llu MB", cardSizeMB);
+  logf("FS total: %llu MB", totalMB);
+  logf("FS used : %llu MB", usedMB);
+  logf("SPI bus: %s @ %lu Hz", sdBusName_, (unsigned long)sdFreq_);
+}
+
+bool StartupSdManager::ensureDirRecursive(const char* path) {
+  String full(path);
+  if (!full.startsWith("/")) {
+    full = "/" + full;
+  }
+
+  int start = 1;
+  while (start > 0 && start < (int)full.length()) {
+    int slash = full.indexOf('/', start);
+    String partial = (slash < 0) ? full : full.substring(0, slash);
+    if (!SD.exists(partial.c_str()) && !SD.mkdir(partial.c_str())) {
+      logf("ERROR: mkdir failed for %s", partial.c_str());
+      return false;
+    }
+    if (slash < 0) {
+      break;
+    }
+    start = slash + 1;
+  }
+
+  return true;
+}
+
+bool StartupSdManager::rewriteFile(const char* path, const char* payload) {
+  if (SD.exists(path) && !SD.remove(path)) {
+    logf("ERROR: failed to erase %s", path);
+    return false;
+  }
+
+  File f = SD.open(path, FILE_WRITE);
+  if (!f) {
+    logf("ERROR: failed to create %s", path);
+    return false;
+  }
+
+  size_t wrote = f.println(payload);
+  f.close();
+  if (wrote == 0) {
+    logf("ERROR: write failed for %s", path);
+    return false;
+  }
+  return true;
+}
+
+void StartupSdManager::permissionsDemo(const char* path) {
+  logf("Permissions demo: FAT has no Unix chmod/chown, use open mode only.");
+  File r = SD.open(path, FILE_READ);
+  if (!r) {
+    logf("Could not open %s as FILE_READ", path);
+    return;
+  }
+  size_t writeInReadMode = r.print("attempt write while opened read-only");
+  if (writeInReadMode == 0) {
+    logf("As expected, FILE_READ write was blocked.");
+  } else {
+    logf("NOTE: FILE_READ write returned %u (unexpected)", (unsigned)writeInReadMode);
+  }
+  r.close();
+}
+
+void StartupSdManager::setStateMounted() {
+  if (watchState_ != SdWatchState::MOUNTED) {
+    logf("EVENT: card inserted/mounted");
+    mountedEventPending_ = true;
+    notify(SdEvent::CARD_MOUNTED, "SD card mounted");
+  }
+  watchState_ = SdWatchState::MOUNTED;
+}
+
+void StartupSdManager::setStateAbsent() {
+  if (watchState_ == SdWatchState::MOUNTED) {
+    logf("EVENT: card removed/unavailable");
+    removedEventPending_ = true;
+    notify(SdEvent::CARD_REMOVED, "SD card removed");
+  } else if (watchState_ != SdWatchState::ABSENT) {
+    logf("EVENT: no card detected");
+    notify(SdEvent::NO_CARD, "Missing SD card / Please insert card to proceed");
+  }
+  SD.end();
+  watchState_ = SdWatchState::ABSENT;
+}

exercises/07_SD_Startup_Watcher/lib/startup_sd/StartupSdManager.h

@@ -0,0 +1,90 @@
+#pragma once
+
+#include <Arduino.h>
+#include <SD.h>
+#include <SPI.h>
+#include <Wire.h>
+#include "tbeam_supreme_adapter.h"
+
+enum class SdWatchState : uint8_t {
+  UNKNOWN = 0,
+  ABSENT,
+  MOUNTED
+};
+
+enum class SdEvent : uint8_t {
+  NO_CARD,
+  CARD_MOUNTED,
+  CARD_REMOVED
+};
+
+using SdStatusCallback = void (*)(SdEvent event, const char* message);
+
+struct SdWatcherConfig {
+  bool enableSdRailCycle = true;
+  bool enablePinDumps = true;
+  bool recoveryRailCycleOnFullScan = true;
+  uint32_t recoveryRailOffMs = 250;
+  uint32_t recoveryRailOnSettleMs = 700;
+  uint32_t startupWarmupMs = 1500;
+  uint32_t pollIntervalAbsentMs = 1000;
+  uint32_t pollIntervalMountedMs = 2000;
+  uint32_t fullScanIntervalMs = 10000;
+  uint8_t votesToPresent = 2;
+  uint8_t votesToAbsent = 5;
+};
+
+class StartupSdManager {
+ public:
+  explicit StartupSdManager(Print& serial = Serial);
+
+  bool begin(const SdWatcherConfig& cfg, SdStatusCallback callback = nullptr);
+  void update();
+
+  bool isMounted() const { return watchState_ == SdWatchState::MOUNTED; }
+  SdWatchState state() const { return watchState_; }
+
+  bool consumeMountedEvent();
+  bool consumeRemovedEvent();
+
+  void printCardInfo();
+  bool ensureDirRecursive(const char* path);
+  bool rewriteFile(const char* path, const char* payload);
+  void permissionsDemo(const char* path);
+
+ private:
+  void logf(const char* fmt, ...);
+  void notify(SdEvent event, const char* message);
+  void forceSpiDeselected();
+  void dumpSdPins(const char* tag);
+  bool initPmuForSdPower();
+  void cycleSdRail(uint32_t offMs = 250, uint32_t onSettleMs = 600);
+  bool tryMountWithBus(SPIClass& bus, const char* busName, uint32_t hz, bool verbose);
+  bool mountPreferred(bool verbose);
+  bool mountCardFullScan();
+  bool verifyMountedCard();
+  const char* cardTypeToString(uint8_t type);
+  void setStateMounted();
+  void setStateAbsent();
+
+  Print& serial_;
+  SdWatcherConfig cfg_{};
+  SdStatusCallback callback_ = nullptr;
+
+  SPIClass sdSpiH_{HSPI};
+  SPIClass sdSpiF_{FSPI};
+  SPIClass* sdSpi_ = nullptr;
+  const char* sdBusName_ = "none";
+  uint32_t sdFreq_ = 0;
+  XPowersLibInterface* pmu_ = nullptr;
+
+  SdWatchState watchState_ = SdWatchState::UNKNOWN;
+  uint8_t presentVotes_ = 0;
+  uint8_t absentVotes_ = 0;
+  uint32_t lastPollMs_ = 0;
+  uint32_t lastFullScanMs_ = 0;
+  uint32_t logSeq_ = 0;
+
+  bool mountedEventPending_ = false;
+  bool removedEventPending_ = false;
+};

exercises/07_SD_Startup_Watcher/lib/startup_sd/library.json

@@ -0,0 +1,12 @@
+{
+  "name": "startup_sd",
+  "version": "0.1.0",
+  "dependencies": [
+    {
+      "name": "XPowersLib"
+    },
+    {
+      "name": "Wire"
+    }
+  ]
+}

exercises/07_SD_Startup_Watcher/platformio.ini

@@ -0,0 +1,37 @@
+; 20260213 ChatGPT
+; $Id$
+; $HeadURL$
+
+[platformio]
+default_envs = node_a
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+monitor_speed = 115200
+lib_deps =
+  lewisxhe/XPowersLib@0.3.3
+  Wire
+  olikraus/U8g2@^2.36.4
+
+; SD pins based on T-Beam S3 core pin mapping
+build_flags =
+  -I ../../shared/boards
+  -I ../../external/microReticulum_Firmware
+  -D BOARD_MODEL=BOARD_TBEAM_S_V1
+  -D OLED_SDA=17
+  -D OLED_SCL=18
+  -D OLED_ADDR=0x3C
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+
+[env:node_a]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"A\"
+
+[env:node_b]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"B\"

exercises/07_SD_Startup_Watcher/src/main.cpp

@@ -0,0 +1,135 @@
+// 20260215 ChatGPT
+// $Id$
+// $HeadURL$
+
+#include <Arduino.h>
+#include <Wire.h>
+#include <U8g2lib.h>
+#include "StartupSdManager.h"
+#include "tbeam_supreme_adapter.h"
+
+#define STARTUP_SERIAL_DELAY_MS 5000
+#ifndef OLED_SDA
+#define OLED_SDA 17
+#endif
+#ifndef OLED_SCL
+#define OLED_SCL 18
+#endif
+#ifndef OLED_ADDR
+#define OLED_ADDR 0x3C
+#endif
+
+static const char* kRootTestFile = "/Exercise_07_test.txt";
+static const char* kNestedDir = "/test/testsub1/testsubsub1";
+static const char* kNestedTestFile = "/test/testsub1/testsubsub1/Exercise_07_test.txt";
+static const char* kPayload = "This is a test";
+static const uint32_t kPeriodicActionMs = 15000;
+
+static U8G2_SH1106_128X64_NONAME_F_HW_I2C g_oled(U8G2_R0, /* reset=*/U8X8_PIN_NONE);
+static StartupSdManager g_sd(Serial);
+static uint32_t g_lastPeriodicActionMs = 0;
+
+static void oledShow3(const char* l1, const char* l2 = nullptr, const char* l3 = nullptr) {
+  g_oled.clearBuffer();
+  g_oled.setFont(u8g2_font_6x10_tf);
+  if (l1) g_oled.drawUTF8(0, 16, l1);
+  if (l2) g_oled.drawUTF8(0, 32, l2);
+  if (l3) g_oled.drawUTF8(0, 48, l3);
+  g_oled.sendBuffer();
+}
+
+static void onSdStatus(SdEvent event, const char* message) {
+  Serial.printf("[SD-STATUS] %s\r\n", message);
+
+  if (event == SdEvent::NO_CARD) {
+    oledShow3("Missing SD card", "Please insert card", "to proceed");
+  } else if (event == SdEvent::CARD_MOUNTED) {
+    oledShow3("SD card ready", "Mounted OK");
+  } else if (event == SdEvent::CARD_REMOVED) {
+    oledShow3("SD card removed", "Please re-insert");
+  }
+}
+
+static void runCardWorkflow() {
+  g_sd.printCardInfo();
+
+  if (!g_sd.rewriteFile(kRootTestFile, kPayload)) {
+    Serial.println("Watcher action: root file write failed");
+    return;
+  }
+  if (!g_sd.ensureDirRecursive(kNestedDir)) {
+    Serial.println("Watcher action: directory creation failed");
+    return;
+  }
+  if (!g_sd.rewriteFile(kNestedTestFile, kPayload)) {
+    Serial.println("Watcher action: nested file write failed");
+    return;
+  }
+
+  g_sd.permissionsDemo(kRootTestFile);
+}
+
+void setup() {
+  Serial.begin(115200);
+  Wire.begin(OLED_SDA, OLED_SCL);
+  g_oled.setI2CAddress(OLED_ADDR << 1);
+  g_oled.begin();
+  oledShow3("Exercise 07", "SD startup watcher", "Booting...");
+
+  Serial.println("[WATCHER: startup]");
+  Serial.printf("Sleeping for %lu ms to allow Serial Monitor connection...\r\n",
+                (unsigned long)STARTUP_SERIAL_DELAY_MS);
+  delay(STARTUP_SERIAL_DELAY_MS);
+
+  Serial.println();
+  Serial.println("==================================================");
+  Serial.println("Exercise 07: SD Startup Watcher (Library Harness)");
+  Serial.println("==================================================");
+  Serial.printf("Pins: CS=%d SCK=%d MISO=%d MOSI=%d\r\n",
+                tbeam_supreme::sdCs(), tbeam_supreme::sdSck(),
+                tbeam_supreme::sdMiso(), tbeam_supreme::sdMosi());
+  Serial.printf("PMU I2C: SDA1=%d SCL1=%d\r\n",
+                tbeam_supreme::i2cSda(), tbeam_supreme::i2cScl());
+  Serial.println("Note: SD must be FAT16/FAT32 for Arduino SD library.\r\n");
+
+  SdWatcherConfig cfg;
+  cfg.enableSdRailCycle = true;
+  cfg.enablePinDumps = true;
+  cfg.startupWarmupMs = 1500;
+  cfg.pollIntervalAbsentMs = 1000;
+  cfg.pollIntervalMountedMs = 2000;
+  cfg.fullScanIntervalMs = 10000;
+  cfg.votesToPresent = 2;
+  cfg.votesToAbsent = 5;
+
+  if (!g_sd.begin(cfg, onSdStatus)) {
+    Serial.println("ERROR: SD watcher init failed");
+  }
+
+  if (g_sd.isMounted()) {
+    runCardWorkflow();
+    g_lastPeriodicActionMs = millis();
+  }
+}
+
+void loop() {
+  g_sd.update();
+
+  if (g_sd.consumeMountedEvent()) {
+    runCardWorkflow();
+    g_lastPeriodicActionMs = millis();
+  }
+
+  if (g_sd.consumeRemovedEvent()) {
+    Serial.println("SD removed, waiting for re-insert...");
+  }
+
+  const uint32_t now = millis();
+  if (g_sd.isMounted() && (uint32_t)(now - g_lastPeriodicActionMs) >= kPeriodicActionMs) {
+    Serial.println("Watcher: periodic mounted check action");
+    runCardWorkflow();
+    g_lastPeriodicActionMs = now;
+  }
+
+  delay(10);
+}

exercises/08_SystemStartup/README.md

@@ -0,0 +1,43 @@
+## Exercise 08: SystemStartup Package Scaffold
+
+This exercise starts a reusable `SystemStartup` package that is intended to be shared by future exercises and field firmware.
+
+Current package responsibilities:
+
+1. Initialize OLED and show boot/status messages.
+2. Initialize SD startup watcher.
+3. Keep SD monitoring active in `loop()` with a single call.
+
+Current integration pattern:
+
+```cpp
+#include "SystemStartup.h"
+
+static SystemStartup g_systemStartup(Serial);
+
+void setup() {
+  Serial.begin(115200);
+  g_systemStartup.begin();
+}
+
+void loop() {
+  g_systemStartup.update();
+  delay(10);
+}
+```
+
+This is the foundation for adding more startup subsystems (RTC sync/check, etc.) behind the same `begin()/update()` API.
+
+## Build
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e node_a
+```
+
+## Upload
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e node_a -t upload --upload-port /dev/ttyACM0
+```

exercises/08_SystemStartup/lib/startup_sd/StartupSdManager.cpp

@@ -0,0 +1,360 @@
+#include "StartupSdManager.h"
+
+#include <stdarg.h>
+#include "driver/gpio.h"
+
+StartupSdManager::StartupSdManager(Print& serial) : serial_(serial) {}
+
+bool StartupSdManager::begin(const SdWatcherConfig& cfg, SdStatusCallback callback) {
+  cfg_ = cfg;
+  callback_ = callback;
+
+  forceSpiDeselected();
+  dumpSdPins("very-early");
+
+  if (!initPmuForSdPower()) {
+    return false;
+  }
+
+  cycleSdRail();
+  delay(cfg_.startupWarmupMs);
+
+  bool warmMounted = false;
+  for (uint8_t i = 0; i < 3; ++i) {
+    if (mountPreferred(false)) {
+      warmMounted = true;
+      break;
+    }
+    delay(200);
+  }
+
+  // Some cards need a longer power/settle window after cold boot.
+  // Before declaring ABSENT, retry with extended settle and a full scan.
+  if (!warmMounted) {
+    logf("Watcher: startup preferred mount failed, retrying with extended settle");
+    cycleSdRail(400, 1200);
+    delay(cfg_.startupWarmupMs + 1500);
+    warmMounted = mountCardFullScan();
+  }
+
+  if (warmMounted) {
+    setStateMounted();
+  } else {
+    setStateAbsent();
+  }
+  return true;
+}
+
+void StartupSdManager::update() {
+  const uint32_t now = millis();
+  const uint32_t pollInterval =
+      (watchState_ == SdWatchState::MOUNTED) ? cfg_.pollIntervalMountedMs : cfg_.pollIntervalAbsentMs;
+
+  if ((uint32_t)(now - lastPollMs_) < pollInterval) {
+    return;
+  }
+  lastPollMs_ = now;
+
+  if (watchState_ == SdWatchState::MOUNTED) {
+    if (verifyMountedCard()) {
+      presentVotes_ = 0;
+      absentVotes_ = 0;
+      return;
+    }
+
+    if (mountPreferred(false) && verifyMountedCard()) {
+      presentVotes_ = 0;
+      absentVotes_ = 0;
+      return;
+    }
+
+    absentVotes_++;
+    presentVotes_ = 0;
+    if (absentVotes_ >= cfg_.votesToAbsent) {
+      setStateAbsent();
+      absentVotes_ = 0;
+    }
+    return;
+  }
+
+  bool mounted = mountPreferred(false);
+  if (!mounted && (uint32_t)(now - lastFullScanMs_) >= cfg_.fullScanIntervalMs) {
+    lastFullScanMs_ = now;
+    if (cfg_.recoveryRailCycleOnFullScan) {
+      logf("Watcher: recovery rail cycle before full scan");
+      cycleSdRail(cfg_.recoveryRailOffMs, cfg_.recoveryRailOnSettleMs);
+      delay(150);
+    }
+    logf("Watcher: preferred probe failed, running full scan");
+    mounted = mountCardFullScan();
+  }
+
+  if (mounted) {
+    presentVotes_++;
+    absentVotes_ = 0;
+    if (presentVotes_ >= cfg_.votesToPresent) {
+      setStateMounted();
+      presentVotes_ = 0;
+    }
+  } else {
+    absentVotes_++;
+    presentVotes_ = 0;
+    if (absentVotes_ >= cfg_.votesToAbsent) {
+      setStateAbsent();
+      absentVotes_ = 0;
+    }
+  }
+}
+
+bool StartupSdManager::consumeMountedEvent() {
+  bool out = mountedEventPending_;
+  mountedEventPending_ = false;
+  return out;
+}
+
+bool StartupSdManager::consumeRemovedEvent() {
+  bool out = removedEventPending_;
+  removedEventPending_ = false;
+  return out;
+}
+
+void StartupSdManager::logf(const char* fmt, ...) {
+  char msg[196];
+  va_list args;
+  va_start(args, fmt);
+  vsnprintf(msg, sizeof(msg), fmt, args);
+  va_end(args);
+  serial_.printf("[%10lu][%06lu] %s\r\n",
+                 (unsigned long)millis(),
+                 (unsigned long)logSeq_++,
+                 msg);
+}
+
+void StartupSdManager::notify(SdEvent event, const char* message) {
+  if (callback_ != nullptr) {
+    callback_(event, message);
+  }
+}
+
+void StartupSdManager::forceSpiDeselected() {
+  pinMode(tbeam_supreme::sdCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  pinMode(tbeam_supreme::imuCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::imuCs(), HIGH);
+}
+
+void StartupSdManager::dumpSdPins(const char* tag) {
+  if (!cfg_.enablePinDumps) {
+    (void)tag;
+    return;
+  }
+
+  const gpio_num_t cs = (gpio_num_t)tbeam_supreme::sdCs();
+  const gpio_num_t sck = (gpio_num_t)tbeam_supreme::sdSck();
+  const gpio_num_t miso = (gpio_num_t)tbeam_supreme::sdMiso();
+  const gpio_num_t mosi = (gpio_num_t)tbeam_supreme::sdMosi();
+  logf("PINS(%s): CS=%d SCK=%d MISO=%d MOSI=%d",
+       tag, gpio_get_level(cs), gpio_get_level(sck), gpio_get_level(miso), gpio_get_level(mosi));
+}
+
+bool StartupSdManager::initPmuForSdPower() {
+  if (!tbeam_supreme::initPmuForPeripherals(pmu_, &serial_)) {
+    logf("ERROR: PMU init failed");
+    return false;
+  }
+  return true;
+}
+
+void StartupSdManager::cycleSdRail(uint32_t offMs, uint32_t onSettleMs) {
+  if (!cfg_.enableSdRailCycle) {
+    return;
+  }
+  if (!pmu_) {
+    logf("SD rail cycle skipped: pmu=null");
+    return;
+  }
+
+  forceSpiDeselected();
+  pmu_->disablePowerOutput(XPOWERS_BLDO1);
+  delay(offMs);
+  pmu_->setPowerChannelVoltage(XPOWERS_BLDO1, 3300);
+  pmu_->enablePowerOutput(XPOWERS_BLDO1);
+  delay(onSettleMs);
+}
+
+bool StartupSdManager::tryMountWithBus(SPIClass& bus, const char* busName, uint32_t hz, bool verbose) {
+  SD.end();
+  bus.end();
+  delay(10);
+  forceSpiDeselected();
+
+  bus.begin(tbeam_supreme::sdSck(), tbeam_supreme::sdMiso(), tbeam_supreme::sdMosi(), tbeam_supreme::sdCs());
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  delay(2);
+  for (int i = 0; i < 10; i++) {
+    bus.transfer(0xFF);
+  }
+  delay(2);
+
+  if (verbose) {
+    logf("SD: trying bus=%s freq=%lu Hz", busName, (unsigned long)hz);
+  }
+
+  if (!SD.begin(tbeam_supreme::sdCs(), bus, hz)) {
+    if (verbose) {
+      logf("SD: mount failed (possible non-FAT format, power, or bus issue)");
+    }
+    return false;
+  }
+
+  if (SD.cardType() == CARD_NONE) {
+    SD.end();
+    return false;
+  }
+
+  sdSpi_ = &bus;
+  sdBusName_ = busName;
+  sdFreq_ = hz;
+  return true;
+}
+
+bool StartupSdManager::mountPreferred(bool verbose) {
+  return tryMountWithBus(sdSpiH_, "HSPI", 400000, verbose);
+}
+
+bool StartupSdManager::mountCardFullScan() {
+  const uint32_t freqs[] = {400000, 1000000, 4000000, 10000000};
+
+  for (uint8_t i = 0; i < (sizeof(freqs) / sizeof(freqs[0])); ++i) {
+    if (tryMountWithBus(sdSpiH_, "HSPI", freqs[i], true)) {
+      logf("SD: card detected and mounted");
+      return true;
+    }
+  }
+  for (uint8_t i = 0; i < (sizeof(freqs) / sizeof(freqs[0])); ++i) {
+    if (tryMountWithBus(sdSpiF_, "FSPI", freqs[i], true)) {
+      logf("SD: card detected and mounted");
+      return true;
+    }
+  }
+
+  logf("SD: begin() failed on all bus/frequency attempts");
+  return false;
+}
+
+bool StartupSdManager::verifyMountedCard() {
+  File root = SD.open("/", FILE_READ);
+  if (!root) {
+    return false;
+  }
+  root.close();
+  return true;
+}
+
+const char* StartupSdManager::cardTypeToString(uint8_t type) {
+  switch (type) {
+    case CARD_MMC:
+      return "MMC";
+    case CARD_SD:
+      return "SDSC";
+    case CARD_SDHC:
+      return "SDHC/SDXC";
+    default:
+      return "UNKNOWN";
+  }
+}
+
+void StartupSdManager::printCardInfo() {
+  uint8_t cardType = SD.cardType();
+  uint64_t cardSizeMB = SD.cardSize() / (1024ULL * 1024ULL);
+  uint64_t totalMB = SD.totalBytes() / (1024ULL * 1024ULL);
+  uint64_t usedMB = SD.usedBytes() / (1024ULL * 1024ULL);
+
+  logf("SD type: %s", cardTypeToString(cardType));
+  logf("SD size: %llu MB", cardSizeMB);
+  logf("FS total: %llu MB", totalMB);
+  logf("FS used : %llu MB", usedMB);
+  logf("SPI bus: %s @ %lu Hz", sdBusName_, (unsigned long)sdFreq_);
+}
+
+bool StartupSdManager::ensureDirRecursive(const char* path) {
+  String full(path);
+  if (!full.startsWith("/")) {
+    full = "/" + full;
+  }
+
+  int start = 1;
+  while (start > 0 && start < (int)full.length()) {
+    int slash = full.indexOf('/', start);
+    String partial = (slash < 0) ? full : full.substring(0, slash);
+    if (!SD.exists(partial.c_str()) && !SD.mkdir(partial.c_str())) {
+      logf("ERROR: mkdir failed for %s", partial.c_str());
+      return false;
+    }
+    if (slash < 0) {
+      break;
+    }
+    start = slash + 1;
+  }
+
+  return true;
+}
+
+bool StartupSdManager::rewriteFile(const char* path, const char* payload) {
+  if (SD.exists(path) && !SD.remove(path)) {
+    logf("ERROR: failed to erase %s", path);
+    return false;
+  }
+
+  File f = SD.open(path, FILE_WRITE);
+  if (!f) {
+    logf("ERROR: failed to create %s", path);
+    return false;
+  }
+
+  size_t wrote = f.println(payload);
+  f.close();
+  if (wrote == 0) {
+    logf("ERROR: write failed for %s", path);
+    return false;
+  }
+  return true;
+}
+
+void StartupSdManager::permissionsDemo(const char* path) {
+  logf("Permissions demo: FAT has no Unix chmod/chown, use open mode only.");
+  File r = SD.open(path, FILE_READ);
+  if (!r) {
+    logf("Could not open %s as FILE_READ", path);
+    return;
+  }
+  size_t writeInReadMode = r.print("attempt write while opened read-only");
+  if (writeInReadMode == 0) {
+    logf("As expected, FILE_READ write was blocked.");
+  } else {
+    logf("NOTE: FILE_READ write returned %u (unexpected)", (unsigned)writeInReadMode);
+  }
+  r.close();
+}
+
+void StartupSdManager::setStateMounted() {
+  if (watchState_ != SdWatchState::MOUNTED) {
+    logf("EVENT: card inserted/mounted");
+    mountedEventPending_ = true;
+    notify(SdEvent::CARD_MOUNTED, "SD card mounted");
+  }
+  watchState_ = SdWatchState::MOUNTED;
+}
+
+void StartupSdManager::setStateAbsent() {
+  if (watchState_ == SdWatchState::MOUNTED) {
+    logf("EVENT: card removed/unavailable");
+    removedEventPending_ = true;
+    notify(SdEvent::CARD_REMOVED, "SD card removed");
+  } else if (watchState_ != SdWatchState::ABSENT) {
+    logf("EVENT: no card detected");
+    notify(SdEvent::NO_CARD, "Missing SD card or invalid FAT16/FAT32 format");
+  }
+  SD.end();
+  watchState_ = SdWatchState::ABSENT;
+}

exercises/08_SystemStartup/lib/startup_sd/StartupSdManager.h

@@ -0,0 +1,90 @@
+#pragma once
+
+#include <Arduino.h>
+#include <SD.h>
+#include <SPI.h>
+#include <Wire.h>
+#include "tbeam_supreme_adapter.h"
+
+enum class SdWatchState : uint8_t {
+  UNKNOWN = 0,
+  ABSENT,
+  MOUNTED
+};
+
+enum class SdEvent : uint8_t {
+  NO_CARD,
+  CARD_MOUNTED,
+  CARD_REMOVED
+};
+
+using SdStatusCallback = void (*)(SdEvent event, const char* message);
+
+struct SdWatcherConfig {
+  bool enableSdRailCycle = true;
+  bool enablePinDumps = true;
+  bool recoveryRailCycleOnFullScan = true;
+  uint32_t recoveryRailOffMs = 250;
+  uint32_t recoveryRailOnSettleMs = 700;
+  uint32_t startupWarmupMs = 1500;
+  uint32_t pollIntervalAbsentMs = 1000;
+  uint32_t pollIntervalMountedMs = 2000;
+  uint32_t fullScanIntervalMs = 10000;
+  uint8_t votesToPresent = 2;
+  uint8_t votesToAbsent = 5;
+};
+
+class StartupSdManager {
+ public:
+  explicit StartupSdManager(Print& serial = Serial);
+
+  bool begin(const SdWatcherConfig& cfg, SdStatusCallback callback = nullptr);
+  void update();
+
+  bool isMounted() const { return watchState_ == SdWatchState::MOUNTED; }
+  SdWatchState state() const { return watchState_; }
+
+  bool consumeMountedEvent();
+  bool consumeRemovedEvent();
+
+  void printCardInfo();
+  bool ensureDirRecursive(const char* path);
+  bool rewriteFile(const char* path, const char* payload);
+  void permissionsDemo(const char* path);
+
+ private:
+  void logf(const char* fmt, ...);
+  void notify(SdEvent event, const char* message);
+  void forceSpiDeselected();
+  void dumpSdPins(const char* tag);
+  bool initPmuForSdPower();
+  void cycleSdRail(uint32_t offMs = 250, uint32_t onSettleMs = 600);
+  bool tryMountWithBus(SPIClass& bus, const char* busName, uint32_t hz, bool verbose);
+  bool mountPreferred(bool verbose);
+  bool mountCardFullScan();
+  bool verifyMountedCard();
+  const char* cardTypeToString(uint8_t type);
+  void setStateMounted();
+  void setStateAbsent();
+
+  Print& serial_;
+  SdWatcherConfig cfg_{};
+  SdStatusCallback callback_ = nullptr;
+
+  SPIClass sdSpiH_{HSPI};
+  SPIClass sdSpiF_{FSPI};
+  SPIClass* sdSpi_ = nullptr;
+  const char* sdBusName_ = "none";
+  uint32_t sdFreq_ = 0;
+  XPowersLibInterface* pmu_ = nullptr;
+
+  SdWatchState watchState_ = SdWatchState::UNKNOWN;
+  uint8_t presentVotes_ = 0;
+  uint8_t absentVotes_ = 0;
+  uint32_t lastPollMs_ = 0;
+  uint32_t lastFullScanMs_ = 0;
+  uint32_t logSeq_ = 0;
+
+  bool mountedEventPending_ = false;
+  bool removedEventPending_ = false;
+};

exercises/08_SystemStartup/lib/startup_sd/library.json

@@ -0,0 +1,12 @@
+{
+  "name": "startup_sd",
+  "version": "0.1.0",
+  "dependencies": [
+    {
+      "name": "XPowersLib"
+    },
+    {
+      "name": "Wire"
+    }
+  ]
+}

exercises/08_SystemStartup/lib/system_startup/SystemStartup.cpp

@@ -0,0 +1,96 @@
+#include "SystemStartup.h"
+
+#include <Wire.h>
+#include <U8g2lib.h>
+
+#ifndef OLED_SDA
+#define OLED_SDA 17
+#endif
+
+#ifndef OLED_SCL
+#define OLED_SCL 18
+#endif
+
+#ifndef OLED_ADDR
+#define OLED_ADDR 0x3C
+#endif
+
+static const bool kEnableOled = true;
+
+static U8G2_SH1106_128X64_NONAME_F_HW_I2C g_oled(U8G2_R0, /* reset=*/U8X8_PIN_NONE);
+static SystemStartup* g_activeSystemStartup = nullptr;
+
+static void forceSpiDeselectedEarly() {
+  pinMode(tbeam_supreme::sdCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  pinMode(tbeam_supreme::imuCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::imuCs(), HIGH);
+}
+
+SystemStartup::SystemStartup(Print& serial) : serial_(serial), sd_(serial) {}
+
+bool SystemStartup::begin(const SystemStartupConfig& cfg, SystemEventCallback callback) {
+  cfg_ = cfg;
+  callback_ = callback;
+  g_activeSystemStartup = this;
+
+  // Match Exercise 05 behavior: deselect SPI devices immediately at startup.
+  forceSpiDeselectedEarly();
+
+  if (kEnableOled) {
+    Wire.begin(OLED_SDA, OLED_SCL);
+    g_oled.setI2CAddress(OLED_ADDR << 1);
+    g_oled.begin();
+  }
+
+  emit(SystemEvent::BOOTING, "System startup booting");
+  oledShow3("System Startup", "Booting...");
+
+  serial_.printf("Sleeping for %lu ms to allow Serial Monitor connection...\r\n",
+                 (unsigned long)cfg_.serialDelayMs);
+  delay(cfg_.serialDelayMs);
+
+  return sd_.begin(cfg_.sd, &SystemStartup::onSdEventThunk);
+}
+
+void SystemStartup::update() {
+  sd_.update();
+}
+
+void SystemStartup::onSdEventThunk(SdEvent event, const char* message) {
+  if (g_activeSystemStartup != nullptr) {
+    g_activeSystemStartup->onSdEvent(event, message);
+  }
+}
+
+void SystemStartup::onSdEvent(SdEvent event, const char* message) {
+  if (event == SdEvent::NO_CARD) {
+    oledShow3("SD missing or", "invalid FAT16/32", "Insert/format card");
+    emit(SystemEvent::SD_MISSING, message);
+  } else if (event == SdEvent::CARD_MOUNTED) {
+    oledShow3("SD card ready", "Mounted OK");
+    emit(SystemEvent::SD_READY, message);
+  } else if (event == SdEvent::CARD_REMOVED) {
+    oledShow3("SD card removed", "Please re-insert");
+    emit(SystemEvent::SD_REMOVED, message);
+  }
+}
+
+void SystemStartup::emit(SystemEvent event, const char* message) {
+  serial_.printf("[SYSTEM] %s\r\n", message);
+  if (callback_ != nullptr) {
+    callback_(event, message);
+  }
+}
+
+void SystemStartup::oledShow3(const char* l1, const char* l2, const char* l3) {
+  if (!kEnableOled) {
+    return;
+  }
+  g_oled.clearBuffer();
+  g_oled.setFont(u8g2_font_6x10_tf);
+  if (l1) g_oled.drawUTF8(0, 16, l1);
+  if (l2) g_oled.drawUTF8(0, 32, l2);
+  if (l3) g_oled.drawUTF8(0, 48, l3);
+  g_oled.sendBuffer();
+}

exercises/08_SystemStartup/lib/system_startup/SystemStartup.h

@@ -0,0 +1,46 @@
+#pragma once
+
+#include <Arduino.h>
+#include "StartupSdManager.h"
+
+// Convenience alias so sketches can use System.println(...) style logging.
+// Arduino exposes Serial, not System, so map System -> Serial.
+#ifndef System
+#define System Serial
+#endif
+
+enum class SystemEvent : uint8_t {
+  BOOTING = 0,
+  SD_MISSING,
+  SD_READY,
+  SD_REMOVED
+};
+
+using SystemEventCallback = void (*)(SystemEvent event, const char* message);
+
+struct SystemStartupConfig {
+  uint32_t serialDelayMs = 5000;
+  SdWatcherConfig sd{};
+};
+
+class SystemStartup {
+ public:
+  explicit SystemStartup(Print& serial = Serial);
+
+  bool begin(const SystemStartupConfig& cfg = SystemStartupConfig{}, SystemEventCallback callback = nullptr);
+  void update();
+
+  bool isSdMounted() const { return sd_.isMounted(); }
+  StartupSdManager& sdManager() { return sd_; }
+
+ private:
+  static void onSdEventThunk(SdEvent event, const char* message);
+  void onSdEvent(SdEvent event, const char* message);
+  void emit(SystemEvent event, const char* message);
+  void oledShow3(const char* l1, const char* l2 = nullptr, const char* l3 = nullptr);
+
+  Print& serial_;
+  SystemStartupConfig cfg_{};
+  SystemEventCallback callback_ = nullptr;
+  StartupSdManager sd_;
+};

exercises/08_SystemStartup/lib/system_startup/library.json

@@ -0,0 +1,15 @@
+{
+  "name": "system_startup",
+  "version": "0.1.0",
+  "dependencies": [
+    {
+      "name": "startup_sd"
+    },
+    {
+      "name": "U8g2"
+    },
+    {
+      "name": "Wire"
+    }
+  ]
+}

exercises/08_SystemStartup/platformio.ini

@@ -0,0 +1,37 @@
+; 20260213 ChatGPT
+; $Id$
+; $HeadURL$
+
+[platformio]
+default_envs = node_a
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+monitor_speed = 115200
+lib_deps =
+  lewisxhe/XPowersLib@0.3.3
+  Wire
+  olikraus/U8g2@^2.36.4
+
+; SD pins based on T-Beam S3 core pin mapping
+build_flags =
+  -I ../../shared/boards
+  -I ../../external/microReticulum_Firmware
+  -D BOARD_MODEL=BOARD_TBEAM_S_V1
+  -D OLED_SDA=17
+  -D OLED_SCL=18
+  -D OLED_ADDR=0x3C
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+
+[env:node_a]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"A\"
+
+[env:node_b]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"B\"

exercises/08_SystemStartup/src/main.cpp

@@ -0,0 +1,21 @@
+// 20260216 ChatGPT
+// $Id$
+// $HeadURL$
+
+#include <Arduino.h>
+#include "SystemStartup.h"
+
+static SystemStartup g_systemStartup(Serial);
+
+void setup() {
+  Serial.begin(115200);
+  System.println("Example 08: setup() called. About to call g_systemStartup.begin().");
+  g_systemStartup.begin();
+  System.println("After g_systemStartup() in setup().");
+}
+
+void loop() {
+  g_systemStartup.update();
+  System.println("Example 08 loop() called and after g_systemStartup.update().");
+  delay(1000);
+}

exercises/09_GPS_Time/README.md

@@ -0,0 +1,52 @@
+## Exercise 09: GPS Time (L76K + UBLOX)
+
+This exercise boots the T-Beam Supreme and verifies GPS behavior at startup.
+
+Important sequence note:
+
+- Exercise 10 (`10_Simple_GPS`) should be completed before this exercise.
+- Exercise 10 README contains the detailed pin-configuration explanation and troubleshooting rationale for why explicit GPS pin mapping is critical on this hardware.
+- If GPS behavior is unexpected here, review Exercise 10 README first, then return to Exercise 9.
+
+Implemented behavior:
+
+1. Initializes PMU, OLED, and SD startup watcher (same startup SD path used in Exercise 08).
+2. Probes GPS at startup for NMEA traffic, module identity, satellite count, and UTC time availability.
+   - Uses explicit GPS UART pins and an active startup probe (multi-baud + common GPS query commands), aligned with the approach validated in Exercise 10.
+3. Supports both module profiles via `platformio.ini` build flags:
+   - `node_a` / `node_b`: `GPS_L76K`
+   - `node_c`: `GPS_UBLOX`
+4. If detected module data conflicts with the selected node profile, OLED shows a `GPS module mismatch` error.
+5. Every minute:
+   - If GPS UTC is valid: shows GPS UTC time and satellites on OLED.
+   - If satellites are seen but UTC is not valid yet: shows that condition and RTC time.
+   - If no satellites: shows:
+     - "Unable to acquire"
+     - "satellites"
+     - "Take me outside so I"
+     - "can see satellites"
+     - plus current RTC time.
+
+Notes:
+
+- GPS time displayed is UTC from NMEA RMC with valid status.
+- Satellite count uses best available from GGA/GSA/GSV.
+- RTC fallback reads PCF8563 via Wire1.
+- For UBLOX hardware use `-e node_c`.
+- The UBLOX MAX-M10S path is given a longer startup window than L76K because cold starts are slower, especially if backup power/orbit data are unavailable.
+- On T-Beam Supreme, `GPS_WAKEUP_PIN=7` is relevant for the L76K variant; the UBLOX MAX-M10S does not use that wake pin in the same way.
+- For fastest UBLOX reacquisition, test with the 18650 attached so the GNSS backup domain can preserve assistance state across resets/power cycles.
+
+## Build
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e node_a
+```
+
+## Upload
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e node_a -t upload --upload-port /dev/ttyACM0
+```

exercises/09_GPS_Time/lib/startup_sd/StartupSdManager.cpp

@@ -0,0 +1,360 @@
+#include "StartupSdManager.h"
+
+#include <stdarg.h>
+#include "driver/gpio.h"
+
+StartupSdManager::StartupSdManager(Print& serial) : serial_(serial) {}
+
+bool StartupSdManager::begin(const SdWatcherConfig& cfg, SdStatusCallback callback) {
+  cfg_ = cfg;
+  callback_ = callback;
+
+  forceSpiDeselected();
+  dumpSdPins("very-early");
+
+  if (!initPmuForSdPower()) {
+    return false;
+  }
+
+  cycleSdRail();
+  delay(cfg_.startupWarmupMs);
+
+  bool warmMounted = false;
+  for (uint8_t i = 0; i < 3; ++i) {
+    if (mountPreferred(false)) {
+      warmMounted = true;
+      break;
+    }
+    delay(200);
+  }
+
+  // Some cards need a longer power/settle window after cold boot.
+  // Before declaring ABSENT, retry with extended settle and a full scan.
+  if (!warmMounted) {
+    logf("Watcher: startup preferred mount failed, retrying with extended settle");
+    cycleSdRail(400, 1200);
+    delay(cfg_.startupWarmupMs + 1500);
+    warmMounted = mountCardFullScan();
+  }
+
+  if (warmMounted) {
+    setStateMounted();
+  } else {
+    setStateAbsent();
+  }
+  return true;
+}
+
+void StartupSdManager::update() {
+  const uint32_t now = millis();
+  const uint32_t pollInterval =
+      (watchState_ == SdWatchState::MOUNTED) ? cfg_.pollIntervalMountedMs : cfg_.pollIntervalAbsentMs;
+
+  if ((uint32_t)(now - lastPollMs_) < pollInterval) {
+    return;
+  }
+  lastPollMs_ = now;
+
+  if (watchState_ == SdWatchState::MOUNTED) {
+    if (verifyMountedCard()) {
+      presentVotes_ = 0;
+      absentVotes_ = 0;
+      return;
+    }
+
+    if (mountPreferred(false) && verifyMountedCard()) {
+      presentVotes_ = 0;
+      absentVotes_ = 0;
+      return;
+    }
+
+    absentVotes_++;
+    presentVotes_ = 0;
+    if (absentVotes_ >= cfg_.votesToAbsent) {
+      setStateAbsent();
+      absentVotes_ = 0;
+    }
+    return;
+  }
+
+  bool mounted = mountPreferred(false);
+  if (!mounted && (uint32_t)(now - lastFullScanMs_) >= cfg_.fullScanIntervalMs) {
+    lastFullScanMs_ = now;
+    if (cfg_.recoveryRailCycleOnFullScan) {
+      logf("Watcher: recovery rail cycle before full scan");
+      cycleSdRail(cfg_.recoveryRailOffMs, cfg_.recoveryRailOnSettleMs);
+      delay(150);
+    }
+    logf("Watcher: preferred probe failed, running full scan");
+    mounted = mountCardFullScan();
+  }
+
+  if (mounted) {
+    presentVotes_++;
+    absentVotes_ = 0;
+    if (presentVotes_ >= cfg_.votesToPresent) {
+      setStateMounted();
+      presentVotes_ = 0;
+    }
+  } else {
+    absentVotes_++;
+    presentVotes_ = 0;
+    if (absentVotes_ >= cfg_.votesToAbsent) {
+      setStateAbsent();
+      absentVotes_ = 0;
+    }
+  }
+}
+
+bool StartupSdManager::consumeMountedEvent() {
+  bool out = mountedEventPending_;
+  mountedEventPending_ = false;
+  return out;
+}
+
+bool StartupSdManager::consumeRemovedEvent() {
+  bool out = removedEventPending_;
+  removedEventPending_ = false;
+  return out;
+}
+
+void StartupSdManager::logf(const char* fmt, ...) {
+  char msg[196];
+  va_list args;
+  va_start(args, fmt);
+  vsnprintf(msg, sizeof(msg), fmt, args);
+  va_end(args);
+  serial_.printf("[%10lu][%06lu] %s\r\n",
+                 (unsigned long)millis(),
+                 (unsigned long)logSeq_++,
+                 msg);
+}
+
+void StartupSdManager::notify(SdEvent event, const char* message) {
+  if (callback_ != nullptr) {
+    callback_(event, message);
+  }
+}
+
+void StartupSdManager::forceSpiDeselected() {
+  pinMode(tbeam_supreme::sdCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  pinMode(tbeam_supreme::imuCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::imuCs(), HIGH);
+}
+
+void StartupSdManager::dumpSdPins(const char* tag) {
+  if (!cfg_.enablePinDumps) {
+    (void)tag;
+    return;
+  }
+
+  const gpio_num_t cs = (gpio_num_t)tbeam_supreme::sdCs();
+  const gpio_num_t sck = (gpio_num_t)tbeam_supreme::sdSck();
+  const gpio_num_t miso = (gpio_num_t)tbeam_supreme::sdMiso();
+  const gpio_num_t mosi = (gpio_num_t)tbeam_supreme::sdMosi();
+  logf("PINS(%s): CS=%d SCK=%d MISO=%d MOSI=%d",
+       tag, gpio_get_level(cs), gpio_get_level(sck), gpio_get_level(miso), gpio_get_level(mosi));
+}
+
+bool StartupSdManager::initPmuForSdPower() {
+  if (!tbeam_supreme::initPmuForPeripherals(pmu_, &serial_)) {
+    logf("ERROR: PMU init failed");
+    return false;
+  }
+  return true;
+}
+
+void StartupSdManager::cycleSdRail(uint32_t offMs, uint32_t onSettleMs) {
+  if (!cfg_.enableSdRailCycle) {
+    return;
+  }
+  if (!pmu_) {
+    logf("SD rail cycle skipped: pmu=null");
+    return;
+  }
+
+  forceSpiDeselected();
+  pmu_->disablePowerOutput(XPOWERS_BLDO1);
+  delay(offMs);
+  pmu_->setPowerChannelVoltage(XPOWERS_BLDO1, 3300);
+  pmu_->enablePowerOutput(XPOWERS_BLDO1);
+  delay(onSettleMs);
+}
+
+bool StartupSdManager::tryMountWithBus(SPIClass& bus, const char* busName, uint32_t hz, bool verbose) {
+  SD.end();
+  bus.end();
+  delay(10);
+  forceSpiDeselected();
+
+  bus.begin(tbeam_supreme::sdSck(), tbeam_supreme::sdMiso(), tbeam_supreme::sdMosi(), tbeam_supreme::sdCs());
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  delay(2);
+  for (int i = 0; i < 10; i++) {
+    bus.transfer(0xFF);
+  }
+  delay(2);
+
+  if (verbose) {
+    logf("SD: trying bus=%s freq=%lu Hz", busName, (unsigned long)hz);
+  }
+
+  if (!SD.begin(tbeam_supreme::sdCs(), bus, hz)) {
+    if (verbose) {
+      logf("SD: mount failed (possible non-FAT format, power, or bus issue)");
+    }
+    return false;
+  }
+
+  if (SD.cardType() == CARD_NONE) {
+    SD.end();
+    return false;
+  }
+
+  sdSpi_ = &bus;
+  sdBusName_ = busName;
+  sdFreq_ = hz;
+  return true;
+}
+
+bool StartupSdManager::mountPreferred(bool verbose) {
+  return tryMountWithBus(sdSpiH_, "HSPI", 400000, verbose);
+}
+
+bool StartupSdManager::mountCardFullScan() {
+  const uint32_t freqs[] = {400000, 1000000, 4000000, 10000000};
+
+  for (uint8_t i = 0; i < (sizeof(freqs) / sizeof(freqs[0])); ++i) {
+    if (tryMountWithBus(sdSpiH_, "HSPI", freqs[i], true)) {
+      logf("SD: card detected and mounted");
+      return true;
+    }
+  }
+  for (uint8_t i = 0; i < (sizeof(freqs) / sizeof(freqs[0])); ++i) {
+    if (tryMountWithBus(sdSpiF_, "FSPI", freqs[i], true)) {
+      logf("SD: card detected and mounted");
+      return true;
+    }
+  }
+
+  logf("SD: begin() failed on all bus/frequency attempts");
+  return false;
+}
+
+bool StartupSdManager::verifyMountedCard() {
+  File root = SD.open("/", FILE_READ);
+  if (!root) {
+    return false;
+  }
+  root.close();
+  return true;
+}
+
+const char* StartupSdManager::cardTypeToString(uint8_t type) {
+  switch (type) {
+    case CARD_MMC:
+      return "MMC";
+    case CARD_SD:
+      return "SDSC";
+    case CARD_SDHC:
+      return "SDHC/SDXC";
+    default:
+      return "UNKNOWN";
+  }
+}
+
+void StartupSdManager::printCardInfo() {
+  uint8_t cardType = SD.cardType();
+  uint64_t cardSizeMB = SD.cardSize() / (1024ULL * 1024ULL);
+  uint64_t totalMB = SD.totalBytes() / (1024ULL * 1024ULL);
+  uint64_t usedMB = SD.usedBytes() / (1024ULL * 1024ULL);
+
+  logf("SD type: %s", cardTypeToString(cardType));
+  logf("SD size: %llu MB", cardSizeMB);
+  logf("FS total: %llu MB", totalMB);
+  logf("FS used : %llu MB", usedMB);
+  logf("SPI bus: %s @ %lu Hz", sdBusName_, (unsigned long)sdFreq_);
+}
+
+bool StartupSdManager::ensureDirRecursive(const char* path) {
+  String full(path);
+  if (!full.startsWith("/")) {
+    full = "/" + full;
+  }
+
+  int start = 1;
+  while (start > 0 && start < (int)full.length()) {
+    int slash = full.indexOf('/', start);
+    String partial = (slash < 0) ? full : full.substring(0, slash);
+    if (!SD.exists(partial.c_str()) && !SD.mkdir(partial.c_str())) {
+      logf("ERROR: mkdir failed for %s", partial.c_str());
+      return false;
+    }
+    if (slash < 0) {
+      break;
+    }
+    start = slash + 1;
+  }
+
+  return true;
+}
+
+bool StartupSdManager::rewriteFile(const char* path, const char* payload) {
+  if (SD.exists(path) && !SD.remove(path)) {
+    logf("ERROR: failed to erase %s", path);
+    return false;
+  }
+
+  File f = SD.open(path, FILE_WRITE);
+  if (!f) {
+    logf("ERROR: failed to create %s", path);
+    return false;
+  }
+
+  size_t wrote = f.println(payload);
+  f.close();
+  if (wrote == 0) {
+    logf("ERROR: write failed for %s", path);
+    return false;
+  }
+  return true;
+}
+
+void StartupSdManager::permissionsDemo(const char* path) {
+  logf("Permissions demo: FAT has no Unix chmod/chown, use open mode only.");
+  File r = SD.open(path, FILE_READ);
+  if (!r) {
+    logf("Could not open %s as FILE_READ", path);
+    return;
+  }
+  size_t writeInReadMode = r.print("attempt write while opened read-only");
+  if (writeInReadMode == 0) {
+    logf("As expected, FILE_READ write was blocked.");
+  } else {
+    logf("NOTE: FILE_READ write returned %u (unexpected)", (unsigned)writeInReadMode);
+  }
+  r.close();
+}
+
+void StartupSdManager::setStateMounted() {
+  if (watchState_ != SdWatchState::MOUNTED) {
+    logf("EVENT: card inserted/mounted");
+    mountedEventPending_ = true;
+    notify(SdEvent::CARD_MOUNTED, "SD card mounted");
+  }
+  watchState_ = SdWatchState::MOUNTED;
+}
+
+void StartupSdManager::setStateAbsent() {
+  if (watchState_ == SdWatchState::MOUNTED) {
+    logf("EVENT: card removed/unavailable");
+    removedEventPending_ = true;
+    notify(SdEvent::CARD_REMOVED, "SD card removed");
+  } else if (watchState_ != SdWatchState::ABSENT) {
+    logf("EVENT: no card detected");
+    notify(SdEvent::NO_CARD, "Missing SD card or invalid FAT16/FAT32 format");
+  }
+  SD.end();
+  watchState_ = SdWatchState::ABSENT;
+}

exercises/09_GPS_Time/lib/startup_sd/StartupSdManager.h

@@ -0,0 +1,90 @@
+#pragma once
+
+#include <Arduino.h>
+#include <SD.h>
+#include <SPI.h>
+#include <Wire.h>
+#include "tbeam_supreme_adapter.h"
+
+enum class SdWatchState : uint8_t {
+  UNKNOWN = 0,
+  ABSENT,
+  MOUNTED
+};
+
+enum class SdEvent : uint8_t {
+  NO_CARD,
+  CARD_MOUNTED,
+  CARD_REMOVED
+};
+
+using SdStatusCallback = void (*)(SdEvent event, const char* message);
+
+struct SdWatcherConfig {
+  bool enableSdRailCycle = true;
+  bool enablePinDumps = true;
+  bool recoveryRailCycleOnFullScan = true;
+  uint32_t recoveryRailOffMs = 250;
+  uint32_t recoveryRailOnSettleMs = 700;
+  uint32_t startupWarmupMs = 1500;
+  uint32_t pollIntervalAbsentMs = 1000;
+  uint32_t pollIntervalMountedMs = 2000;
+  uint32_t fullScanIntervalMs = 10000;
+  uint8_t votesToPresent = 2;
+  uint8_t votesToAbsent = 5;
+};
+
+class StartupSdManager {
+ public:
+  explicit StartupSdManager(Print& serial = Serial);
+
+  bool begin(const SdWatcherConfig& cfg, SdStatusCallback callback = nullptr);
+  void update();
+
+  bool isMounted() const { return watchState_ == SdWatchState::MOUNTED; }
+  SdWatchState state() const { return watchState_; }
+
+  bool consumeMountedEvent();
+  bool consumeRemovedEvent();
+
+  void printCardInfo();
+  bool ensureDirRecursive(const char* path);
+  bool rewriteFile(const char* path, const char* payload);
+  void permissionsDemo(const char* path);
+
+ private:
+  void logf(const char* fmt, ...);
+  void notify(SdEvent event, const char* message);
+  void forceSpiDeselected();
+  void dumpSdPins(const char* tag);
+  bool initPmuForSdPower();
+  void cycleSdRail(uint32_t offMs = 250, uint32_t onSettleMs = 600);
+  bool tryMountWithBus(SPIClass& bus, const char* busName, uint32_t hz, bool verbose);
+  bool mountPreferred(bool verbose);
+  bool mountCardFullScan();
+  bool verifyMountedCard();
+  const char* cardTypeToString(uint8_t type);
+  void setStateMounted();
+  void setStateAbsent();
+
+  Print& serial_;
+  SdWatcherConfig cfg_{};
+  SdStatusCallback callback_ = nullptr;
+
+  SPIClass sdSpiH_{HSPI};
+  SPIClass sdSpiF_{FSPI};
+  SPIClass* sdSpi_ = nullptr;
+  const char* sdBusName_ = "none";
+  uint32_t sdFreq_ = 0;
+  XPowersLibInterface* pmu_ = nullptr;
+
+  SdWatchState watchState_ = SdWatchState::UNKNOWN;
+  uint8_t presentVotes_ = 0;
+  uint8_t absentVotes_ = 0;
+  uint32_t lastPollMs_ = 0;
+  uint32_t lastFullScanMs_ = 0;
+  uint32_t logSeq_ = 0;
+
+  bool mountedEventPending_ = false;
+  bool removedEventPending_ = false;
+};

exercises/09_GPS_Time/lib/startup_sd/library.json

@@ -0,0 +1,12 @@
+{
+  "name": "startup_sd",
+  "version": "0.1.0",
+  "dependencies": [
+    {
+      "name": "XPowersLib"
+    },
+    {
+      "name": "Wire"
+    }
+  ]
+}

exercises/09_GPS_Time/lib/system_startup/SystemStartup.cpp

@@ -0,0 +1,96 @@
+#include "SystemStartup.h"
+
+#include <Wire.h>
+#include <U8g2lib.h>
+
+#ifndef OLED_SDA
+#define OLED_SDA 17
+#endif
+
+#ifndef OLED_SCL
+#define OLED_SCL 18
+#endif
+
+#ifndef OLED_ADDR
+#define OLED_ADDR 0x3C
+#endif
+
+static const bool kEnableOled = true;
+
+static U8G2_SH1106_128X64_NONAME_F_HW_I2C g_oled(U8G2_R0, /* reset=*/U8X8_PIN_NONE);
+static SystemStartup* g_activeSystemStartup = nullptr;
+
+static void forceSpiDeselectedEarly() {
+  pinMode(tbeam_supreme::sdCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  pinMode(tbeam_supreme::imuCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::imuCs(), HIGH);
+}
+
+SystemStartup::SystemStartup(Print& serial) : serial_(serial), sd_(serial) {}
+
+bool SystemStartup::begin(const SystemStartupConfig& cfg, SystemEventCallback callback) {
+  cfg_ = cfg;
+  callback_ = callback;
+  g_activeSystemStartup = this;
+
+  // Match Exercise 05 behavior: deselect SPI devices immediately at startup.
+  forceSpiDeselectedEarly();
+
+  if (kEnableOled) {
+    Wire.begin(OLED_SDA, OLED_SCL);
+    g_oled.setI2CAddress(OLED_ADDR << 1);
+    g_oled.begin();
+  }
+
+  emit(SystemEvent::BOOTING, "System startup booting");
+  oledShow3("System Startup", "Booting...");
+
+  serial_.printf("Sleeping for %lu ms to allow Serial Monitor connection...\r\n",
+                 (unsigned long)cfg_.serialDelayMs);
+  delay(cfg_.serialDelayMs);
+
+  return sd_.begin(cfg_.sd, &SystemStartup::onSdEventThunk);
+}
+
+void SystemStartup::update() {
+  sd_.update();
+}
+
+void SystemStartup::onSdEventThunk(SdEvent event, const char* message) {
+  if (g_activeSystemStartup != nullptr) {
+    g_activeSystemStartup->onSdEvent(event, message);
+  }
+}
+
+void SystemStartup::onSdEvent(SdEvent event, const char* message) {
+  if (event == SdEvent::NO_CARD) {
+    oledShow3("SD missing or", "invalid FAT16/32", "Insert/format card");
+    emit(SystemEvent::SD_MISSING, message);
+  } else if (event == SdEvent::CARD_MOUNTED) {
+    oledShow3("SD card ready", "Mounted OK");
+    emit(SystemEvent::SD_READY, message);
+  } else if (event == SdEvent::CARD_REMOVED) {
+    oledShow3("SD card removed", "Please re-insert");
+    emit(SystemEvent::SD_REMOVED, message);
+  }
+}
+
+void SystemStartup::emit(SystemEvent event, const char* message) {
+  serial_.printf("[SYSTEM] %s\r\n", message);
+  if (callback_ != nullptr) {
+    callback_(event, message);
+  }
+}
+
+void SystemStartup::oledShow3(const char* l1, const char* l2, const char* l3) {
+  if (!kEnableOled) {
+    return;
+  }
+  g_oled.clearBuffer();
+  g_oled.setFont(u8g2_font_6x10_tf);
+  if (l1) g_oled.drawUTF8(0, 16, l1);
+  if (l2) g_oled.drawUTF8(0, 32, l2);
+  if (l3) g_oled.drawUTF8(0, 48, l3);
+  g_oled.sendBuffer();
+}

exercises/09_GPS_Time/lib/system_startup/SystemStartup.h

@@ -0,0 +1,46 @@
+#pragma once
+
+#include <Arduino.h>
+#include "StartupSdManager.h"
+
+// Convenience alias so sketches can use System.println(...) style logging.
+// Arduino exposes Serial, not System, so map System -> Serial.
+#ifndef System
+#define System Serial
+#endif
+
+enum class SystemEvent : uint8_t {
+  BOOTING = 0,
+  SD_MISSING,
+  SD_READY,
+  SD_REMOVED
+};
+
+using SystemEventCallback = void (*)(SystemEvent event, const char* message);
+
+struct SystemStartupConfig {
+  uint32_t serialDelayMs = 5000;
+  SdWatcherConfig sd{};
+};
+
+class SystemStartup {
+ public:
+  explicit SystemStartup(Print& serial = Serial);
+
+  bool begin(const SystemStartupConfig& cfg = SystemStartupConfig{}, SystemEventCallback callback = nullptr);
+  void update();
+
+  bool isSdMounted() const { return sd_.isMounted(); }
+  StartupSdManager& sdManager() { return sd_; }
+
+ private:
+  static void onSdEventThunk(SdEvent event, const char* message);
+  void onSdEvent(SdEvent event, const char* message);
+  void emit(SystemEvent event, const char* message);
+  void oledShow3(const char* l1, const char* l2 = nullptr, const char* l3 = nullptr);
+
+  Print& serial_;
+  SystemStartupConfig cfg_{};
+  SystemEventCallback callback_ = nullptr;
+  StartupSdManager sd_;
+};

exercises/09_GPS_Time/lib/system_startup/library.json

@@ -0,0 +1,15 @@
+{
+  "name": "system_startup",
+  "version": "0.1.0",
+  "dependencies": [
+    {
+      "name": "startup_sd"
+    },
+    {
+      "name": "U8g2"
+    },
+    {
+      "name": "Wire"
+    }
+  ]
+}

exercises/09_GPS_Time/platformio.ini

@@ -0,0 +1,48 @@
+; 20260213 ChatGPT
+; $Id$
+; $HeadURL$
+
+[platformio]
+default_envs = node_a
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+monitor_speed = 115200
+lib_deps =
+  lewisxhe/XPowersLib@0.3.3
+  Wire
+  olikraus/U8g2@^2.36.4
+
+; SD pins based on T-Beam S3 core pin mapping
+build_flags =
+  -I ../../shared/boards
+  -I ../../external/microReticulum_Firmware
+  -D BOARD_MODEL=BOARD_TBEAM_S_V1
+  -D OLED_SDA=17
+  -D OLED_SCL=18
+  -D OLED_ADDR=0x3C
+  -D GPS_RX_PIN=9
+  -D GPS_TX_PIN=8
+  -D GPS_WAKEUP_PIN=7
+  -D GPS_1PPS_PIN=6
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+  -D GPS_L76K
+
+[env:node_a]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"A\"
+
+[env:node_b]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"B\"
+
+[env:node_c]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"C\"
+  -D GPS_UBLOX

exercises/10_Simple_GPS/README.md

@@ -0,0 +1,98 @@
+## Exercise 10: Simple GPS (No SD)
+
+Goal: verify GPS satellite and UTC time acquisition on T-Beam Supreme using OLED-only status updates.
+
+## Current behavior
+
+1. Boots PMU, OLED, RTC, and GPS UART.
+2. Runs an active startup GPS probe (multi-baud + query commands) to detect GPS serial traffic.
+3. Every 30 seconds:
+   - Shows `Trying to locate satellites` + `NMEA seen: yes/no` + current RTC time.
+   - Continues parsing GPS NMEA data.
+   - If GPS UTC is valid, shows GPS UTC + satellite count + `NMEA seen: yes/no`.
+   - Otherwise shows `Take me outside` + `NMEA seen: yes/no` + RTC.
+4. No SD card logic is used in this exercise.
+
+## Walk-through: original approach and why
+
+Initial implementation used a minimal/simple GPS strategy:
+
+1. Power up PMU rails using the existing T-Beam adapter.
+2. Start `Serial1` at 9600 baud.
+3. Parse incoming NMEA (`GGA/GSV/RMC`) passively.
+4. Show periodic OLED status every 30 seconds.
+
+Why this was chosen:
+
+- It is the smallest path to validate basic GPS lock/time behavior.
+- It avoids introducing SD complexity while isolating GPS.
+- It is easy for field testing (OLED-first, battery-powered).
+
+## What was discovered by comparing with Meshtastic
+
+Meshtastic GPS handling is more defensive and hardware-aware in principle:
+
+1. It uses a board variant that provides explicit GPS pin mapping for the T-Beam Supreme path.
+2. It initializes GPS serial with explicit RX/TX pins and larger receive buffers.
+3. It performs active startup probing (commands + response checks), not only passive listening.
+4. It attempts detection across known module families and may try multiple serial settings.
+5. It manages GNSS-related power/standby states deliberately (rather than assuming default UART traffic immediately appears).
+
+## What differed in this exercise and likely caused the issue
+
+The first Exercise 10 version was built on `esp32-s3-devkitc-1` with conditional pin usage.
+
+- If GPS pin macros are not present, `Serial1` can start on default pins.
+- That can produce `NMEA seen: no` forever even outdoors, because firmware is listening on the wrong UART pins.
+
+## Corrections applied after Meshtastic review
+
+1. Added explicit GPS pin defines in `platformio.ini`:
+   - `GPS_RX_PIN=9`
+   - `GPS_TX_PIN=8`
+   - `GPS_WAKEUP_PIN=7`
+   - `GPS_1PPS_PIN=6`
+2. Forced UART startup using explicit RX/TX pins.
+3. Added startup multi-baud active probe and common GPS query commands.
+4. Added OLED `NMEA seen: yes/no` so field tests distinguish:
+   - `no sky fix yet` vs
+   - `no GPS serial traffic at all`.
+
+## Field Test Checklist
+
+1. Flash and reboot outdoors with clear sky view.
+2. Confirm the OLED updates every 30 seconds.
+3. Watch for this expected progression:
+   - `Trying to locate satellites` + `NMEA seen: no`
+   - then `Trying to locate satellites` + `NMEA seen: yes`
+   - then either:
+     - `GPS lock acquired` with UTC and satellite count, or
+     - `Take me outside` if no fix yet.
+4. Keep unit stationary for 2-5 minutes for first lock after cold start.
+
+Interpretation guide:
+
+- `NMEA seen: no`: likely UART/pin/baud/module-power communication issue.
+- `NMEA seen: yes` + no lock: GPS is talking, but no valid fix yet (sky view/time-to-first-fix issue).
+- `GPS lock acquired`: fix is valid; UTC and satellites are available from GPS.
+- RTC line updates every 30 seconds: loop is alive and retry cycle is running.
+
+If still failing:
+
+1. Capture serial log from boot through at least 2 full 30-second cycles.
+2. Note whether `NMEA seen` ever changes from `no` to `yes`.
+3. Record whether GPS startup probe reports traffic at any baud rate.
+
+## Build
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e node_a
+```
+
+## Upload
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e node_a -t upload --upload-port /dev/ttyACM0
+```

exercises/10_Simple_GPS/platformio.ini

@@ -0,0 +1,47 @@
+; 20260217 ChatGPT
+; $Id$
+; $HeadURL$
+
+[platformio]
+default_envs = node_a
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+monitor_speed = 115200
+lib_deps =
+  lewisxhe/XPowersLib@0.3.3
+  Wire
+  olikraus/U8g2@^2.36.4
+
+build_flags =
+  -I ../../shared/boards
+  -I ../../external/microReticulum_Firmware
+  -D BOARD_MODEL=BOARD_TBEAM_S_V1
+  -D OLED_SDA=17
+  -D OLED_SCL=18
+  -D OLED_ADDR=0x3C
+  -D GPS_RX_PIN=9
+  -D GPS_TX_PIN=8
+  -D GPS_WAKEUP_PIN=7
+  -D GPS_1PPS_PIN=6
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+  -D GPS_L76K
+
+[env:node_a]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"A\"
+
+[env:node_b]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"B\"
+
+[env:node_c]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"C\"
+  -D GPS_UBLOX

exercises/10_Simple_GPS/src/main.cpp

@@ -0,0 +1,431 @@
+// 20260217 ChatGPT
+// $Id$
+// $HeadURL$
+
+#include <Arduino.h>
+#include <Wire.h>
+#include <U8g2lib.h>
+
+#include "tbeam_supreme_adapter.h"
+
+#ifndef OLED_SDA
+#define OLED_SDA 17
+#endif
+
+#ifndef OLED_SCL
+#define OLED_SCL 18
+#endif
+
+#ifndef OLED_ADDR
+#define OLED_ADDR 0x3C
+#endif
+
+#ifndef RTC_I2C_ADDR
+#define RTC_I2C_ADDR 0x51
+#endif
+
+#ifndef GPS_BAUD
+#define GPS_BAUD 9600
+#endif
+
+static const uint32_t kSerialDelayMs = 5000;
+static const uint32_t kReportIntervalMs = 30000;
+
+static XPowersLibInterface* g_pmu = nullptr;
+static U8G2_SH1106_128X64_NONAME_F_HW_I2C g_oled(U8G2_R0, /* reset=*/U8X8_PIN_NONE);
+static HardwareSerial g_gpsSerial(1);
+
+static uint32_t g_logSeq = 0;
+static uint32_t g_lastReportMs = 0;
+static uint32_t g_gpsBaud = GPS_BAUD;
+
+static char g_gpsLine[128];
+static size_t g_gpsLineLen = 0;
+
+struct RtcDateTime {
+  uint16_t year;
+  uint8_t month;
+  uint8_t day;
+  uint8_t hour;
+  uint8_t minute;
+  uint8_t second;
+};
+
+struct GpsState {
+  bool sawAnySentence = false;
+  uint8_t satsUsed = 0;
+  uint8_t satsInView = 0;
+
+  bool hasValidUtc = false;
+  uint16_t utcYear = 0;
+  uint8_t utcMonth = 0;
+  uint8_t utcDay = 0;
+  uint8_t utcHour = 0;
+  uint8_t utcMinute = 0;
+  uint8_t utcSecond = 0;
+};
+
+static GpsState g_gps;
+
+static void logf(const char* fmt, ...) {
+  char msg[220];
+  va_list args;
+  va_start(args, fmt);
+  vsnprintf(msg, sizeof(msg), fmt, args);
+  va_end(args);
+  Serial.printf("[%10lu][%06lu] %s\r\n", (unsigned long)millis(), (unsigned long)g_logSeq++, msg);
+}
+
+static void oledShowLines(const char* l1,
+                          const char* l2 = nullptr,
+                          const char* l3 = nullptr,
+                          const char* l4 = nullptr,
+                          const char* l5 = nullptr) {
+  g_oled.clearBuffer();
+  g_oled.setFont(u8g2_font_5x8_tf);
+  if (l1) g_oled.drawUTF8(0, 12, l1);
+  if (l2) g_oled.drawUTF8(0, 24, l2);
+  if (l3) g_oled.drawUTF8(0, 36, l3);
+  if (l4) g_oled.drawUTF8(0, 48, l4);
+  if (l5) g_oled.drawUTF8(0, 60, l5);
+  g_oled.sendBuffer();
+}
+
+static uint8_t fromBcd(uint8_t b) {
+  return ((b >> 4U) * 10U) + (b & 0x0FU);
+}
+
+static bool rtcRead(RtcDateTime& out, bool& lowVoltageFlag) {
+  Wire1.beginTransmission(RTC_I2C_ADDR);
+  Wire1.write(0x02);
+  if (Wire1.endTransmission(false) != 0) {
+    return false;
+  }
+
+  const uint8_t need = 7;
+  uint8_t got = Wire1.requestFrom((int)RTC_I2C_ADDR, (int)need);
+  if (got != need) {
+    return false;
+  }
+
+  uint8_t sec = Wire1.read();
+  uint8_t min = Wire1.read();
+  uint8_t hour = Wire1.read();
+  uint8_t day = Wire1.read();
+  (void)Wire1.read();
+  uint8_t month = Wire1.read();
+  uint8_t year = Wire1.read();
+
+  lowVoltageFlag = (sec & 0x80U) != 0;
+  out.second = fromBcd(sec & 0x7FU);
+  out.minute = fromBcd(min & 0x7FU);
+  out.hour = fromBcd(hour & 0x3FU);
+  out.day = fromBcd(day & 0x3FU);
+  out.month = fromBcd(month & 0x1FU);
+  uint8_t yy = fromBcd(year);
+  bool century = (month & 0x80U) != 0;
+  out.year = century ? (1900U + yy) : (2000U + yy);
+  return true;
+}
+
+static String formatRtcNow() {
+  RtcDateTime now{};
+  bool lowV = false;
+  if (!rtcRead(now, lowV)) {
+    return "RTC read failed";
+  }
+
+  char buf[48];
+  snprintf(buf,
+           sizeof(buf),
+           "RTC %04u-%02u-%02u %02u:%02u:%02u%s",
+           (unsigned)now.year,
+           (unsigned)now.month,
+           (unsigned)now.day,
+           (unsigned)now.hour,
+           (unsigned)now.minute,
+           (unsigned)now.second,
+           lowV ? " !LOWV" : "");
+  return String(buf);
+}
+
+static bool parseUInt2(const char* s, uint8_t& out) {
+  if (!s || !isdigit((unsigned char)s[0]) || !isdigit((unsigned char)s[1])) {
+    return false;
+  }
+  out = (uint8_t)((s[0] - '0') * 10 + (s[1] - '0'));
+  return true;
+}
+
+static void parseGga(char* fields[], int count) {
+  if (count <= 7) {
+    return;
+  }
+  int sats = atoi(fields[7]);
+  if (sats >= 0 && sats <= 255) {
+    g_gps.satsUsed = (uint8_t)sats;
+  }
+}
+
+static void parseGsv(char* fields[], int count) {
+  if (count <= 3) {
+    return;
+  }
+  int sats = atoi(fields[3]);
+  if (sats >= 0 && sats <= 255) {
+    g_gps.satsInView = (uint8_t)sats;
+  }
+}
+
+static void parseRmc(char* fields[], int count) {
+  if (count <= 9) {
+    return;
+  }
+
+  const char* utc = fields[1];
+  const char* status = fields[2];
+  const char* date = fields[9];
+
+  if (!status || status[0] != 'A') {
+    return;
+  }
+
+  if (!utc || strlen(utc) < 6 || !date || strlen(date) < 6) {
+    return;
+  }
+
+  uint8_t hh = 0, mm = 0, ss = 0;
+  uint8_t dd = 0, mo = 0, yy = 0;
+  if (!parseUInt2(utc + 0, hh) || !parseUInt2(utc + 2, mm) || !parseUInt2(utc + 4, ss)) {
+    return;
+  }
+  if (!parseUInt2(date + 0, dd) || !parseUInt2(date + 2, mo) || !parseUInt2(date + 4, yy)) {
+    return;
+  }
+
+  g_gps.utcHour = hh;
+  g_gps.utcMinute = mm;
+  g_gps.utcSecond = ss;
+  g_gps.utcDay = dd;
+  g_gps.utcMonth = mo;
+  g_gps.utcYear = (uint16_t)(2000U + yy);
+  g_gps.hasValidUtc = true;
+}
+
+static void processNmeaLine(char* line) {
+  if (!line || line[0] != '$') {
+    return;
+  }
+
+  g_gps.sawAnySentence = true;
+
+  char* star = strchr(line, '*');
+  if (star) {
+    *star = '\0';
+  }
+
+  char* fields[24] = {0};
+  int count = 0;
+  char* saveptr = nullptr;
+  char* tok = strtok_r(line, ",", &saveptr);
+  while (tok && count < 24) {
+    fields[count++] = tok;
+    tok = strtok_r(nullptr, ",", &saveptr);
+  }
+
+  if (count <= 0 || !fields[0]) {
+    return;
+  }
+
+  const char* header = fields[0];
+  size_t n = strlen(header);
+  if (n < 6) {
+    return;
+  }
+
+  const char* type = header + (n - 3);
+  if (strcmp(type, "GGA") == 0) {
+    parseGga(fields, count);
+  } else if (strcmp(type, "GSV") == 0) {
+    parseGsv(fields, count);
+  } else if (strcmp(type, "RMC") == 0) {
+    parseRmc(fields, count);
+  }
+}
+
+static void pollGpsSerial() {
+  while (g_gpsSerial.available() > 0) {
+    char c = (char)g_gpsSerial.read();
+    if (c == '\r') {
+      continue;
+    }
+    if (c == '\n') {
+      if (g_gpsLineLen > 0) {
+        g_gpsLine[g_gpsLineLen] = '\0';
+        processNmeaLine(g_gpsLine);
+        g_gpsLineLen = 0;
+      }
+      continue;
+    }
+
+    if (g_gpsLineLen + 1 < sizeof(g_gpsLine)) {
+      g_gpsLine[g_gpsLineLen++] = c;
+    } else {
+      g_gpsLineLen = 0;
+    }
+  }
+}
+
+static void startGpsUart(uint32_t baud) {
+  g_gpsSerial.end();
+  delay(20);
+  g_gpsSerial.setRxBufferSize(1024);
+  g_gpsSerial.begin(baud, SERIAL_8N1, GPS_RX_PIN, GPS_TX_PIN);
+  g_gpsBaud = baud;
+}
+
+static bool collectGpsTraffic(uint32_t windowMs) {
+  uint32_t start = millis();
+  size_t bytesSeen = 0;
+  while ((uint32_t)(millis() - start) < windowMs) {
+    while (g_gpsSerial.available() > 0) {
+      (void)g_gpsSerial.read();
+      bytesSeen++;
+    }
+    pollGpsSerial();
+    delay(2);
+  }
+  return bytesSeen > 0 || g_gps.sawAnySentence;
+}
+
+static bool probeGpsAtBaud(uint32_t baud) {
+  startGpsUart(baud);
+  logf("Probing GPS at %lu baud...", (unsigned long)baud);
+  if (collectGpsTraffic(700)) {
+    return true;
+  }
+
+  // Try common query/wake commands used by MTK/L76K and related chipsets.
+  g_gpsSerial.write("$PCAS06,0*1B\r\n");     // Request module SW text
+  g_gpsSerial.write("$PMTK605*31\r\n");      // MTK firmware query
+  g_gpsSerial.write("$PQTMVERNO*58\r\n");    // Quectel LC86 query
+  g_gpsSerial.write("$PMTK353,1,1,1,1,1*2A\r\n");
+  g_gpsSerial.write("$PMTK314,0,1,0,1,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0*29\r\n");
+
+  return collectGpsTraffic(1200);
+}
+
+static void initialGpsProbe() {
+  const uint32_t bauds[] = {GPS_BAUD, 115200, 38400, 57600, 19200};
+  for (size_t i = 0; i < sizeof(bauds) / sizeof(bauds[0]); ++i) {
+    if (probeGpsAtBaud(bauds[i])) {
+      logf("GPS traffic detected at %lu baud", (unsigned long)g_gpsBaud);
+      return;
+    }
+  }
+  logf("No GPS traffic detected during startup probe");
+}
+
+static uint8_t bestSatelliteCount() {
+  return (g_gps.satsUsed > g_gps.satsInView) ? g_gps.satsUsed : g_gps.satsInView;
+}
+
+static void showTryingMessage() {
+  String rtc = formatRtcNow();
+  oledShowLines("Trying to locate",
+                "satellites",
+                g_gps.sawAnySentence ? "NMEA seen: yes" : "NMEA seen: no",
+                rtc.c_str());
+  logf("Trying to locate satellites. %s", rtc.c_str());
+}
+
+static void showStatusMessage() {
+  uint8_t sats = bestSatelliteCount();
+
+  if (g_gps.hasValidUtc) {
+    char line2[40];
+    char line3[28];
+    snprintf(line2,
+             sizeof(line2),
+             "GPS UTC %04u-%02u-%02u",
+             (unsigned)g_gps.utcYear,
+             (unsigned)g_gps.utcMonth,
+             (unsigned)g_gps.utcDay);
+    snprintf(line3,
+             sizeof(line3),
+             "%02u:%02u:%02u  sats:%u",
+             (unsigned)g_gps.utcHour,
+             (unsigned)g_gps.utcMinute,
+             (unsigned)g_gps.utcSecond,
+             (unsigned)sats);
+    oledShowLines("GPS lock acquired",
+                  line2,
+                  line3,
+                  g_gps.sawAnySentence ? "NMEA seen: yes" : "NMEA seen: no");
+    logf("GPS lock acquired. %s  sats=%u", line3, (unsigned)sats);
+    return;
+  }
+
+  String rtc = formatRtcNow();
+  oledShowLines("Take me outside",
+                "No GPS time/sats yet",
+                g_gps.sawAnySentence ? "NMEA seen: yes" : "NMEA seen: no",
+                rtc.c_str());
+  logf("Take me outside. sats=%u, has_utc=%s, nmea_seen=%s. %s",
+       (unsigned)sats,
+       g_gps.hasValidUtc ? "yes" : "no",
+       g_gps.sawAnySentence ? "yes" : "no",
+       rtc.c_str());
+}
+
+void setup() {
+  Serial.begin(115200);
+  delay(kSerialDelayMs);
+
+  Serial.println("\r\n==================================================");
+  Serial.println("Exercise 10: Simple GPS (No SD)");
+  Serial.println("==================================================");
+
+  if (!tbeam_supreme::initPmuForPeripherals(g_pmu, &Serial)) {
+    logf("PMU init failed");
+  }
+
+  Wire.begin(OLED_SDA, OLED_SCL);
+  g_oled.setI2CAddress(OLED_ADDR << 1);
+  g_oled.begin();
+  oledShowLines("Simple GPS", "Booting...");
+
+#ifdef GPS_1PPS_PIN
+  pinMode(GPS_1PPS_PIN, INPUT);
+#endif
+
+#ifdef GPS_WAKEUP_PIN
+  // Keep wake pin in a neutral state similar to Meshtastic behavior.
+  pinMode(GPS_WAKEUP_PIN, INPUT);
+#endif
+
+  startGpsUart(GPS_BAUD);
+  logf("GPS UART started: RX=%d TX=%d baud=%lu", GPS_RX_PIN, GPS_TX_PIN, (unsigned long)g_gpsBaud);
+  initialGpsProbe();
+
+  showTryingMessage();
+  g_lastReportMs = millis();
+}
+
+void loop() {
+  pollGpsSerial();
+
+  uint32_t now = millis();
+  if ((uint32_t)(now - g_lastReportMs) >= kReportIntervalMs) {
+    g_lastReportMs = now;
+
+    showTryingMessage();
+    uint32_t start = millis();
+    while ((uint32_t)(millis() - start) < 2000) {
+      pollGpsSerial();
+      delay(5);
+    }
+
+    showStatusMessage();
+  }
+}

exercises/11_Set_RTC2GPS/README.md

@@ -0,0 +1,33 @@
+## Exercise 11: Set RTC to GPS (1PPS Discipline)
+
+This exercise extends Exercise 9 behavior (GPS + SD + OLED) and disciplines the onboard RTC from GPS UTC using the GPS `1PPS` (pulse-per-second) timing signal.
+
+Implemented behavior:
+
+1. Boots PMU, OLED, SD watcher, and GPS UART using the same T-Beam Supreme pin mapping from prior exercises.
+2. Parses NMEA (`RMC`, `GGA`, `GSV`) to track UTC validity and satellite counts.
+3. Every 1 minute, attempts to set RTC from GPS:
+   - Uses latest valid GPS UTC.
+   - Waits for next `1PPS` rising edge.
+   - Sets RTC to GPS time aligned to that edge (UTC + 1 second).
+4. Appends event records to SD file:
+   - Path: `/gps/discipline_rtc.log`
+   - Append-only writes (`FILE_APPEND`)
+   - Format:
+     - `YYYYMMDD_HH24MISS_z\t set RTC to GPS using 1PPS pulse-per-second discipline\trtc-gps drift=+/-Ns`
+5. OLED success message shows RTC disciplined confirmation and timestamp.
+6. If GPS time cannot be determined (or 1PPS edge is not seen in timeout), OLED shows failure status and the loop delays 30 seconds before retry.
+
+## Build
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e node_a
+```
+
+## Upload
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e node_a -t upload --upload-port /dev/ttyACM0
+```

exercises/11_Set_RTC2GPS/lib/startup_sd/StartupSdManager.cpp

@@ -0,0 +1,360 @@
+#include "StartupSdManager.h"
+
+#include <stdarg.h>
+#include "driver/gpio.h"
+
+StartupSdManager::StartupSdManager(Print& serial) : serial_(serial) {}
+
+bool StartupSdManager::begin(const SdWatcherConfig& cfg, SdStatusCallback callback) {
+  cfg_ = cfg;
+  callback_ = callback;
+
+  forceSpiDeselected();
+  dumpSdPins("very-early");
+
+  if (!initPmuForSdPower()) {
+    return false;
+  }
+
+  cycleSdRail();
+  delay(cfg_.startupWarmupMs);
+
+  bool warmMounted = false;
+  for (uint8_t i = 0; i < 3; ++i) {
+    if (mountPreferred(false)) {
+      warmMounted = true;
+      break;
+    }
+    delay(200);
+  }
+
+  // Some cards need a longer power/settle window after cold boot.
+  // Before declaring ABSENT, retry with extended settle and a full scan.
+  if (!warmMounted) {
+    logf("Watcher: startup preferred mount failed, retrying with extended settle");
+    cycleSdRail(400, 1200);
+    delay(cfg_.startupWarmupMs + 1500);
+    warmMounted = mountCardFullScan();
+  }
+
+  if (warmMounted) {
+    setStateMounted();
+  } else {
+    setStateAbsent();
+  }
+  return true;
+}
+
+void StartupSdManager::update() {
+  const uint32_t now = millis();
+  const uint32_t pollInterval =
+      (watchState_ == SdWatchState::MOUNTED) ? cfg_.pollIntervalMountedMs : cfg_.pollIntervalAbsentMs;
+
+  if ((uint32_t)(now - lastPollMs_) < pollInterval) {
+    return;
+  }
+  lastPollMs_ = now;
+
+  if (watchState_ == SdWatchState::MOUNTED) {
+    if (verifyMountedCard()) {
+      presentVotes_ = 0;
+      absentVotes_ = 0;
+      return;
+    }
+
+    if (mountPreferred(false) && verifyMountedCard()) {
+      presentVotes_ = 0;
+      absentVotes_ = 0;
+      return;
+    }
+
+    absentVotes_++;
+    presentVotes_ = 0;
+    if (absentVotes_ >= cfg_.votesToAbsent) {
+      setStateAbsent();
+      absentVotes_ = 0;
+    }
+    return;
+  }
+
+  bool mounted = mountPreferred(false);
+  if (!mounted && (uint32_t)(now - lastFullScanMs_) >= cfg_.fullScanIntervalMs) {
+    lastFullScanMs_ = now;
+    if (cfg_.recoveryRailCycleOnFullScan) {
+      logf("Watcher: recovery rail cycle before full scan");
+      cycleSdRail(cfg_.recoveryRailOffMs, cfg_.recoveryRailOnSettleMs);
+      delay(150);
+    }
+    logf("Watcher: preferred probe failed, running full scan");
+    mounted = mountCardFullScan();
+  }
+
+  if (mounted) {
+    presentVotes_++;
+    absentVotes_ = 0;
+    if (presentVotes_ >= cfg_.votesToPresent) {
+      setStateMounted();
+      presentVotes_ = 0;
+    }
+  } else {
+    absentVotes_++;
+    presentVotes_ = 0;
+    if (absentVotes_ >= cfg_.votesToAbsent) {
+      setStateAbsent();
+      absentVotes_ = 0;
+    }
+  }
+}
+
+bool StartupSdManager::consumeMountedEvent() {
+  bool out = mountedEventPending_;
+  mountedEventPending_ = false;
+  return out;
+}
+
+bool StartupSdManager::consumeRemovedEvent() {
+  bool out = removedEventPending_;
+  removedEventPending_ = false;
+  return out;
+}
+
+void StartupSdManager::logf(const char* fmt, ...) {
+  char msg[196];
+  va_list args;
+  va_start(args, fmt);
+  vsnprintf(msg, sizeof(msg), fmt, args);
+  va_end(args);
+  serial_.printf("[%10lu][%06lu] %s\r\n",
+                 (unsigned long)millis(),
+                 (unsigned long)logSeq_++,
+                 msg);
+}
+
+void StartupSdManager::notify(SdEvent event, const char* message) {
+  if (callback_ != nullptr) {
+    callback_(event, message);
+  }
+}
+
+void StartupSdManager::forceSpiDeselected() {
+  pinMode(tbeam_supreme::sdCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  pinMode(tbeam_supreme::imuCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::imuCs(), HIGH);
+}
+
+void StartupSdManager::dumpSdPins(const char* tag) {
+  if (!cfg_.enablePinDumps) {
+    (void)tag;
+    return;
+  }
+
+  const gpio_num_t cs = (gpio_num_t)tbeam_supreme::sdCs();
+  const gpio_num_t sck = (gpio_num_t)tbeam_supreme::sdSck();
+  const gpio_num_t miso = (gpio_num_t)tbeam_supreme::sdMiso();
+  const gpio_num_t mosi = (gpio_num_t)tbeam_supreme::sdMosi();
+  logf("PINS(%s): CS=%d SCK=%d MISO=%d MOSI=%d",
+       tag, gpio_get_level(cs), gpio_get_level(sck), gpio_get_level(miso), gpio_get_level(mosi));
+}
+
+bool StartupSdManager::initPmuForSdPower() {
+  if (!tbeam_supreme::initPmuForPeripherals(pmu_, &serial_)) {
+    logf("ERROR: PMU init failed");
+    return false;
+  }
+  return true;
+}
+
+void StartupSdManager::cycleSdRail(uint32_t offMs, uint32_t onSettleMs) {
+  if (!cfg_.enableSdRailCycle) {
+    return;
+  }
+  if (!pmu_) {
+    logf("SD rail cycle skipped: pmu=null");
+    return;
+  }
+
+  forceSpiDeselected();
+  pmu_->disablePowerOutput(XPOWERS_BLDO1);
+  delay(offMs);
+  pmu_->setPowerChannelVoltage(XPOWERS_BLDO1, 3300);
+  pmu_->enablePowerOutput(XPOWERS_BLDO1);
+  delay(onSettleMs);
+}
+
+bool StartupSdManager::tryMountWithBus(SPIClass& bus, const char* busName, uint32_t hz, bool verbose) {
+  SD.end();
+  bus.end();
+  delay(10);
+  forceSpiDeselected();
+
+  bus.begin(tbeam_supreme::sdSck(), tbeam_supreme::sdMiso(), tbeam_supreme::sdMosi(), tbeam_supreme::sdCs());
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  delay(2);
+  for (int i = 0; i < 10; i++) {
+    bus.transfer(0xFF);
+  }
+  delay(2);
+
+  if (verbose) {
+    logf("SD: trying bus=%s freq=%lu Hz", busName, (unsigned long)hz);
+  }
+
+  if (!SD.begin(tbeam_supreme::sdCs(), bus, hz)) {
+    if (verbose) {
+      logf("SD: mount failed (possible non-FAT format, power, or bus issue)");
+    }
+    return false;
+  }
+
+  if (SD.cardType() == CARD_NONE) {
+    SD.end();
+    return false;
+  }
+
+  sdSpi_ = &bus;
+  sdBusName_ = busName;
+  sdFreq_ = hz;
+  return true;
+}
+
+bool StartupSdManager::mountPreferred(bool verbose) {
+  return tryMountWithBus(sdSpiH_, "HSPI", 400000, verbose);
+}
+
+bool StartupSdManager::mountCardFullScan() {
+  const uint32_t freqs[] = {400000, 1000000, 4000000, 10000000};
+
+  for (uint8_t i = 0; i < (sizeof(freqs) / sizeof(freqs[0])); ++i) {
+    if (tryMountWithBus(sdSpiH_, "HSPI", freqs[i], true)) {
+      logf("SD: card detected and mounted");
+      return true;
+    }
+  }
+  for (uint8_t i = 0; i < (sizeof(freqs) / sizeof(freqs[0])); ++i) {
+    if (tryMountWithBus(sdSpiF_, "FSPI", freqs[i], true)) {
+      logf("SD: card detected and mounted");
+      return true;
+    }
+  }
+
+  logf("SD: begin() failed on all bus/frequency attempts");
+  return false;
+}
+
+bool StartupSdManager::verifyMountedCard() {
+  File root = SD.open("/", FILE_READ);
+  if (!root) {
+    return false;
+  }
+  root.close();
+  return true;
+}
+
+const char* StartupSdManager::cardTypeToString(uint8_t type) {
+  switch (type) {
+    case CARD_MMC:
+      return "MMC";
+    case CARD_SD:
+      return "SDSC";
+    case CARD_SDHC:
+      return "SDHC/SDXC";
+    default:
+      return "UNKNOWN";
+  }
+}
+
+void StartupSdManager::printCardInfo() {
+  uint8_t cardType = SD.cardType();
+  uint64_t cardSizeMB = SD.cardSize() / (1024ULL * 1024ULL);
+  uint64_t totalMB = SD.totalBytes() / (1024ULL * 1024ULL);
+  uint64_t usedMB = SD.usedBytes() / (1024ULL * 1024ULL);
+
+  logf("SD type: %s", cardTypeToString(cardType));
+  logf("SD size: %llu MB", cardSizeMB);
+  logf("FS total: %llu MB", totalMB);
+  logf("FS used : %llu MB", usedMB);
+  logf("SPI bus: %s @ %lu Hz", sdBusName_, (unsigned long)sdFreq_);
+}
+
+bool StartupSdManager::ensureDirRecursive(const char* path) {
+  String full(path);
+  if (!full.startsWith("/")) {
+    full = "/" + full;
+  }
+
+  int start = 1;
+  while (start > 0 && start < (int)full.length()) {
+    int slash = full.indexOf('/', start);
+    String partial = (slash < 0) ? full : full.substring(0, slash);
+    if (!SD.exists(partial.c_str()) && !SD.mkdir(partial.c_str())) {
+      logf("ERROR: mkdir failed for %s", partial.c_str());
+      return false;
+    }
+    if (slash < 0) {
+      break;
+    }
+    start = slash + 1;
+  }
+
+  return true;
+}
+
+bool StartupSdManager::rewriteFile(const char* path, const char* payload) {
+  if (SD.exists(path) && !SD.remove(path)) {
+    logf("ERROR: failed to erase %s", path);
+    return false;
+  }
+
+  File f = SD.open(path, FILE_WRITE);
+  if (!f) {
+    logf("ERROR: failed to create %s", path);
+    return false;
+  }
+
+  size_t wrote = f.println(payload);
+  f.close();
+  if (wrote == 0) {
+    logf("ERROR: write failed for %s", path);
+    return false;
+  }
+  return true;
+}
+
+void StartupSdManager::permissionsDemo(const char* path) {
+  logf("Permissions demo: FAT has no Unix chmod/chown, use open mode only.");
+  File r = SD.open(path, FILE_READ);
+  if (!r) {
+    logf("Could not open %s as FILE_READ", path);
+    return;
+  }
+  size_t writeInReadMode = r.print("attempt write while opened read-only");
+  if (writeInReadMode == 0) {
+    logf("As expected, FILE_READ write was blocked.");
+  } else {
+    logf("NOTE: FILE_READ write returned %u (unexpected)", (unsigned)writeInReadMode);
+  }
+  r.close();
+}
+
+void StartupSdManager::setStateMounted() {
+  if (watchState_ != SdWatchState::MOUNTED) {
+    logf("EVENT: card inserted/mounted");
+    mountedEventPending_ = true;
+    notify(SdEvent::CARD_MOUNTED, "SD card mounted");
+  }
+  watchState_ = SdWatchState::MOUNTED;
+}
+
+void StartupSdManager::setStateAbsent() {
+  if (watchState_ == SdWatchState::MOUNTED) {
+    logf("EVENT: card removed/unavailable");
+    removedEventPending_ = true;
+    notify(SdEvent::CARD_REMOVED, "SD card removed");
+  } else if (watchState_ != SdWatchState::ABSENT) {
+    logf("EVENT: no card detected");
+    notify(SdEvent::NO_CARD, "Missing SD card or invalid FAT16/FAT32 format");
+  }
+  SD.end();
+  watchState_ = SdWatchState::ABSENT;
+}

exercises/11_Set_RTC2GPS/lib/startup_sd/StartupSdManager.h

@@ -0,0 +1,90 @@
+#pragma once
+
+#include <Arduino.h>
+#include <SD.h>
+#include <SPI.h>
+#include <Wire.h>
+#include "tbeam_supreme_adapter.h"
+
+enum class SdWatchState : uint8_t {
+  UNKNOWN = 0,
+  ABSENT,
+  MOUNTED
+};
+
+enum class SdEvent : uint8_t {
+  NO_CARD,
+  CARD_MOUNTED,
+  CARD_REMOVED
+};
+
+using SdStatusCallback = void (*)(SdEvent event, const char* message);
+
+struct SdWatcherConfig {
+  bool enableSdRailCycle = true;
+  bool enablePinDumps = true;
+  bool recoveryRailCycleOnFullScan = true;
+  uint32_t recoveryRailOffMs = 250;
+  uint32_t recoveryRailOnSettleMs = 700;
+  uint32_t startupWarmupMs = 1500;
+  uint32_t pollIntervalAbsentMs = 1000;
+  uint32_t pollIntervalMountedMs = 2000;
+  uint32_t fullScanIntervalMs = 10000;
+  uint8_t votesToPresent = 2;
+  uint8_t votesToAbsent = 5;
+};
+
+class StartupSdManager {
+ public:
+  explicit StartupSdManager(Print& serial = Serial);
+
+  bool begin(const SdWatcherConfig& cfg, SdStatusCallback callback = nullptr);
+  void update();
+
+  bool isMounted() const { return watchState_ == SdWatchState::MOUNTED; }
+  SdWatchState state() const { return watchState_; }
+
+  bool consumeMountedEvent();
+  bool consumeRemovedEvent();
+
+  void printCardInfo();
+  bool ensureDirRecursive(const char* path);
+  bool rewriteFile(const char* path, const char* payload);
+  void permissionsDemo(const char* path);
+
+ private:
+  void logf(const char* fmt, ...);
+  void notify(SdEvent event, const char* message);
+  void forceSpiDeselected();
+  void dumpSdPins(const char* tag);
+  bool initPmuForSdPower();
+  void cycleSdRail(uint32_t offMs = 250, uint32_t onSettleMs = 600);
+  bool tryMountWithBus(SPIClass& bus, const char* busName, uint32_t hz, bool verbose);
+  bool mountPreferred(bool verbose);
+  bool mountCardFullScan();
+  bool verifyMountedCard();
+  const char* cardTypeToString(uint8_t type);
+  void setStateMounted();
+  void setStateAbsent();
+
+  Print& serial_;
+  SdWatcherConfig cfg_{};
+  SdStatusCallback callback_ = nullptr;
+
+  SPIClass sdSpiH_{HSPI};
+  SPIClass sdSpiF_{FSPI};
+  SPIClass* sdSpi_ = nullptr;
+  const char* sdBusName_ = "none";
+  uint32_t sdFreq_ = 0;
+  XPowersLibInterface* pmu_ = nullptr;
+
+  SdWatchState watchState_ = SdWatchState::UNKNOWN;
+  uint8_t presentVotes_ = 0;
+  uint8_t absentVotes_ = 0;
+  uint32_t lastPollMs_ = 0;
+  uint32_t lastFullScanMs_ = 0;
+  uint32_t logSeq_ = 0;
+
+  bool mountedEventPending_ = false;
+  bool removedEventPending_ = false;
+};

exercises/11_Set_RTC2GPS/lib/startup_sd/library.json

@@ -0,0 +1,12 @@
+{
+  "name": "startup_sd",
+  "version": "0.1.0",
+  "dependencies": [
+    {
+      "name": "XPowersLib"
+    },
+    {
+      "name": "Wire"
+    }
+  ]
+}

exercises/11_Set_RTC2GPS/platformio.ini

@@ -0,0 +1,43 @@
+; 20260213 ChatGPT
+; $Id$
+; $HeadURL$
+
+[platformio]
+default_envs = node_a
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+monitor_speed = 115200
+extra_scripts = pre:scripts/set_build_epoch.py
+lib_deps =
+  lewisxhe/XPowersLib@0.3.3
+  Wire
+  olikraus/U8g2@^2.36.4
+
+; SD pins based on T-Beam S3 core pin mapping
+build_flags =
+  -I ../../shared/boards
+  -I ../../external/microReticulum_Firmware
+  -D BOARD_MODEL=BOARD_TBEAM_S_V1
+  -D OLED_SDA=17
+  -D OLED_SCL=18
+  -D OLED_ADDR=0x3C
+  -D GPS_RX_PIN=9
+  -D GPS_TX_PIN=8
+  -D GPS_WAKEUP_PIN=7
+  -D GPS_1PPS_PIN=6
+  -D GPS_L76K
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+
+[env:node_a]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"A\"
+
+[env:node_b]
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"B\"

exercises/11_Set_RTC2GPS/scripts/set_build_epoch.py

@@ -0,0 +1,12 @@
+import time
+Import("env")
+
+epoch = int(time.time())
+utc_tag = time.strftime("%Y%m%d_%H%M%S_z", time.gmtime(epoch))
+
+env.Append(
+    CPPDEFINES=[
+        ("FW_BUILD_EPOCH", str(epoch)),
+        ("FW_BUILD_UTC", '\\"%s\\"' % utc_tag),
+    ]
+)

exercises/11_Set_RTC2GPS/src/main.cpp

@@ -0,0 +1,786 @@
+// 20260217 ChatGPT
+// $Id$
+// $HeadURL$
+
+#include <Arduino.h>
+#include <Wire.h>
+#include <SD.h>
+#include <U8g2lib.h>
+
+#include "StartupSdManager.h"
+#include "tbeam_supreme_adapter.h"
+
+#ifndef OLED_SDA
+#define OLED_SDA 17
+#endif
+
+#ifndef OLED_SCL
+#define OLED_SCL 18
+#endif
+
+#ifndef OLED_ADDR
+#define OLED_ADDR 0x3C
+#endif
+
+#ifndef RTC_I2C_ADDR
+#define RTC_I2C_ADDR 0x51
+#endif
+
+#ifndef GPS_BAUD
+#define GPS_BAUD 9600
+#endif
+
+#ifndef FILE_APPEND
+#define FILE_APPEND FILE_WRITE
+#endif
+
+#ifndef FW_BUILD_EPOCH
+#define FW_BUILD_EPOCH 0
+#endif
+
+#ifndef FW_BUILD_UTC
+#define FW_BUILD_UTC "unknown"
+#endif
+
+static const uint32_t kSerialDelayMs = 5000;
+static const uint32_t kLoopMsDiscipline = 60000;
+static const uint32_t kNoTimeDelayMs = 30000;
+static const uint32_t kGpsStartupProbeMs = 20000;
+static const uint32_t kPpsWaitTimeoutMs = 1500;
+
+static XPowersLibInterface* g_pmu = nullptr;
+static StartupSdManager g_sd(Serial);
+static U8G2_SH1106_128X64_NONAME_F_HW_I2C g_oled(U8G2_R0, /* reset=*/U8X8_PIN_NONE);
+static HardwareSerial g_gpsSerial(1);
+
+static uint32_t g_logSeq = 0;
+static uint32_t g_nextDisciplineMs = 0;
+static bool g_gpsPathReady = false;
+
+static char g_gpsLine[128];
+static size_t g_gpsLineLen = 0;
+
+static volatile uint32_t g_ppsEdgeCount = 0;
+
+struct DateTime {
+  uint16_t year;
+  uint8_t month;
+  uint8_t day;
+  uint8_t hour;
+  uint8_t minute;
+  uint8_t second;
+};
+
+struct GpsState {
+  bool sawAnySentence = false;
+  bool hasValidUtc = false;
+  bool hasValidPosition = false;
+  bool hasValidAltitude = false;
+  uint8_t satsUsed = 0;
+  uint8_t satsInView = 0;
+  float hdop = -1.0f;
+  float altitudeM = 0.0f;
+  double latitudeDeg = 0.0;
+  double longitudeDeg = 0.0;
+  DateTime utc{};
+  uint32_t lastUtcMs = 0;
+};
+
+static GpsState g_gps;
+
+static void logf(const char* fmt, ...) {
+  char msg[240];
+  va_list args;
+  va_start(args, fmt);
+  vsnprintf(msg, sizeof(msg), fmt, args);
+  va_end(args);
+  Serial.printf("[%10lu][%06lu] %s\r\n", (unsigned long)millis(), (unsigned long)g_logSeq++, msg);
+}
+
+static void oledShowLines(const char* l1,
+                          const char* l2 = nullptr,
+                          const char* l3 = nullptr,
+                          const char* l4 = nullptr,
+                          const char* l5 = nullptr) {
+  g_oled.clearBuffer();
+  g_oled.setFont(u8g2_font_5x8_tf);
+  if (l1) g_oled.drawUTF8(0, 12, l1);
+  if (l2) g_oled.drawUTF8(0, 24, l2);
+  if (l3) g_oled.drawUTF8(0, 36, l3);
+  if (l4) g_oled.drawUTF8(0, 48, l4);
+  if (l5) g_oled.drawUTF8(0, 60, l5);
+  g_oled.sendBuffer();
+}
+
+static uint8_t toBcd(uint8_t v) {
+  return (uint8_t)(((v / 10U) << 4U) | (v % 10U));
+}
+
+static uint8_t fromBcd(uint8_t b) {
+  return (uint8_t)(((b >> 4U) * 10U) + (b & 0x0FU));
+}
+
+static bool rtcRead(DateTime& out, bool& lowVoltageFlag) {
+  Wire1.beginTransmission(RTC_I2C_ADDR);
+  Wire1.write(0x02);
+  if (Wire1.endTransmission(false) != 0) {
+    return false;
+  }
+
+  const uint8_t need = 7;
+  uint8_t got = Wire1.requestFrom((int)RTC_I2C_ADDR, (int)need);
+  if (got != need) {
+    return false;
+  }
+
+  uint8_t sec = Wire1.read();
+  uint8_t min = Wire1.read();
+  uint8_t hour = Wire1.read();
+  uint8_t day = Wire1.read();
+  (void)Wire1.read();
+  uint8_t month = Wire1.read();
+  uint8_t year = Wire1.read();
+
+  lowVoltageFlag = (sec & 0x80U) != 0;
+  out.second = fromBcd(sec & 0x7FU);
+  out.minute = fromBcd(min & 0x7FU);
+  out.hour = fromBcd(hour & 0x3FU);
+  out.day = fromBcd(day & 0x3FU);
+  out.month = fromBcd(month & 0x1FU);
+  uint8_t yy = fromBcd(year);
+  bool century = (month & 0x80U) != 0;
+  out.year = century ? (1900U + yy) : (2000U + yy);
+  return true;
+}
+
+static bool rtcWrite(const DateTime& dt) {
+  Wire1.beginTransmission(RTC_I2C_ADDR);
+  Wire1.write(0x02);
+  Wire1.write(toBcd(dt.second & 0x7FU));
+  Wire1.write(toBcd(dt.minute));
+  Wire1.write(toBcd(dt.hour));
+  Wire1.write(toBcd(dt.day));
+  Wire1.write(0x00);
+
+  uint8_t monthReg = toBcd(dt.month);
+  if (dt.year < 2000U) {
+    monthReg |= 0x80U;
+  }
+  Wire1.write(monthReg);
+  Wire1.write(toBcd((uint8_t)(dt.year % 100U)));
+
+  return Wire1.endTransmission() == 0;
+}
+
+static bool isLeapYear(uint16_t y) {
+  return ((y % 4U) == 0U && (y % 100U) != 0U) || ((y % 400U) == 0U);
+}
+
+static uint8_t daysInMonth(uint16_t year, uint8_t month) {
+  static const uint8_t kDays[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
+  if (month == 2) {
+    return (uint8_t)(isLeapYear(year) ? 29 : 28);
+  }
+  if (month >= 1 && month <= 12) {
+    return kDays[month - 1];
+  }
+  return 30;
+}
+
+static bool isValidDateTime(const DateTime& dt) {
+  if (dt.year < 2000U || dt.year > 2099U) return false;
+  if (dt.month < 1 || dt.month > 12) return false;
+  if (dt.day < 1 || dt.day > daysInMonth(dt.year, dt.month)) return false;
+  if (dt.hour > 23 || dt.minute > 59 || dt.second > 59) return false;
+  return true;
+}
+
+static int64_t daysFromCivil(int y, unsigned m, unsigned d) {
+  y -= (m <= 2);
+  const int era = (y >= 0 ? y : y - 399) / 400;
+  const unsigned yoe = (unsigned)(y - era * 400);
+  const unsigned doy = (153 * (m + (m > 2 ? (unsigned)-3 : 9)) + 2) / 5 + d - 1;
+  const unsigned doe = yoe * 365 + yoe / 4 - yoe / 100 + doy;
+  return era * 146097 + (int)doe - 719468;
+}
+
+static int64_t toEpochSeconds(const DateTime& dt) {
+  int64_t days = daysFromCivil((int)dt.year, dt.month, dt.day);
+  return days * 86400LL + (int64_t)dt.hour * 3600LL + (int64_t)dt.minute * 60LL + (int64_t)dt.second;
+}
+
+static bool fromEpochSeconds(int64_t sec, DateTime& out) {
+  if (sec < 0) {
+    return false;
+  }
+
+  int64_t days = sec / 86400LL;
+  int64_t rem = sec % 86400LL;
+  if (rem < 0) {
+    rem += 86400LL;
+    days -= 1;
+  }
+
+  out.hour = (uint8_t)(rem / 3600LL);
+  rem %= 3600LL;
+  out.minute = (uint8_t)(rem / 60LL);
+  out.second = (uint8_t)(rem % 60LL);
+
+  days += 719468;
+  const int era = (days >= 0 ? days : days - 146096) / 146097;
+  const unsigned doe = (unsigned)(days - era * 146097);
+  const unsigned yoe = (doe - doe / 1460 + doe / 36524 - doe / 146096) / 365;
+  int y = (int)yoe + era * 400;
+  const unsigned doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
+  const unsigned mp = (5 * doy + 2) / 153;
+  const unsigned d = doy - (153 * mp + 2) / 5 + 1;
+  const unsigned m = mp + (mp < 10 ? 3 : (unsigned)-9);
+  y += (m <= 2);
+
+  out.year = (uint16_t)y;
+  out.month = (uint8_t)m;
+  out.day = (uint8_t)d;
+  return isValidDateTime(out);
+}
+
+static void addOneSecond(DateTime& dt) {
+  int64_t t = toEpochSeconds(dt);
+  DateTime out{};
+  if (fromEpochSeconds(t + 1, out)) {
+    dt = out;
+  }
+}
+
+static void formatUtcCompact(const DateTime& dt, char* out, size_t outLen) {
+  snprintf(out,
+           outLen,
+           "%04u%02u%02u_%02u%02u%02u_z",
+           (unsigned)dt.year,
+           (unsigned)dt.month,
+           (unsigned)dt.day,
+           (unsigned)dt.hour,
+           (unsigned)dt.minute,
+           (unsigned)dt.second);
+}
+
+static void formatUtcHuman(const DateTime& dt, char* out, size_t outLen) {
+  snprintf(out,
+           outLen,
+           "%04u-%02u-%02u %02u:%02u:%02u UTC",
+           (unsigned)dt.year,
+           (unsigned)dt.month,
+           (unsigned)dt.day,
+           (unsigned)dt.hour,
+           (unsigned)dt.minute,
+           (unsigned)dt.second);
+}
+
+static bool parseUInt2(const char* s, uint8_t& out) {
+  if (!s || !isdigit((unsigned char)s[0]) || !isdigit((unsigned char)s[1])) {
+    return false;
+  }
+  out = (uint8_t)((s[0] - '0') * 10 + (s[1] - '0'));
+  return true;
+}
+
+static bool parseNmeaCoordToDecimal(const char* raw, const char* hemi, bool isLat, double& outDeg) {
+  if (!raw || !hemi || raw[0] == '\0' || hemi[0] == '\0') {
+    return false;
+  }
+
+  // NMEA uses ddmm.mmmm (lat) and dddmm.mmmm (lon), with leading zeros preserved.
+  // Parse from string slices so longitudes like 071xx.xxxx do not collapse to 7xx.xxxx.
+  int degDigits = isLat ? 2 : 3;
+  size_t n = strlen(raw);
+  if (n <= (size_t)degDigits + 2) {
+    return false;
+  }
+
+  for (int i = 0; i < degDigits; ++i) {
+    if (!isdigit((unsigned char)raw[i])) {
+      return false;
+    }
+  }
+
+  char degBuf[4] = {0};
+  memcpy(degBuf, raw, degDigits);
+  int deg = atoi(degBuf);
+
+  const char* minPtr = raw + degDigits;
+  double minutes = atof(minPtr);
+  if (minutes < 0.0 || minutes >= 60.0) {
+    return false;
+  }
+
+  double dec = (double)deg + (minutes / 60.0);
+  char h = (char)toupper((unsigned char)hemi[0]);
+  if (h == 'S' || h == 'W') {
+    dec = -dec;
+  } else if (h != 'N' && h != 'E') {
+    return false;
+  }
+
+  outDeg = dec;
+  return true;
+}
+
+static void parseGga(char* fields[], int count) {
+  if (count <= 7) {
+    return;
+  }
+  const char* latRaw = (count > 2) ? fields[2] : nullptr;
+  const char* latHem = (count > 3) ? fields[3] : nullptr;
+  const char* lonRaw = (count > 4) ? fields[4] : nullptr;
+  const char* lonHem = (count > 5) ? fields[5] : nullptr;
+  int sats = atoi(fields[7]);
+  if (sats >= 0 && sats <= 255) {
+    g_gps.satsUsed = (uint8_t)sats;
+  }
+  if (count > 8 && fields[8] && fields[8][0] != '\0') {
+    g_gps.hdop = (float)atof(fields[8]);
+  }
+  if (count > 9 && fields[9] && fields[9][0] != '\0') {
+    g_gps.altitudeM = (float)atof(fields[9]);
+    g_gps.hasValidAltitude = true;
+  }
+
+  // Position fallback from GGA so we still log coordinates if RMC position is missing.
+  double lat = 0.0;
+  double lon = 0.0;
+  if (parseNmeaCoordToDecimal(latRaw, latHem, true, lat) &&
+      parseNmeaCoordToDecimal(lonRaw, lonHem, false, lon)) {
+    g_gps.latitudeDeg = lat;
+    g_gps.longitudeDeg = lon;
+    g_gps.hasValidPosition = true;
+  }
+}
+
+static void parseGsv(char* fields[], int count) {
+  if (count <= 3) {
+    return;
+  }
+  int sats = atoi(fields[3]);
+  if (sats >= 0 && sats <= 255) {
+    g_gps.satsInView = (uint8_t)sats;
+  }
+}
+
+static void parseRmc(char* fields[], int count) {
+  if (count <= 9) {
+    return;
+  }
+
+  const char* utc = fields[1];
+  const char* status = fields[2];
+  const char* latRaw = fields[3];
+  const char* latHem = fields[4];
+  const char* lonRaw = fields[5];
+  const char* lonHem = fields[6];
+  const char* date = fields[9];
+
+  if (!status || status[0] != 'A') {
+    return;
+  }
+
+  if (!utc || strlen(utc) < 6 || !date || strlen(date) < 6) {
+    return;
+  }
+
+  uint8_t hh = 0, mm = 0, ss = 0;
+  uint8_t dd = 0, mo = 0, yy = 0;
+  if (!parseUInt2(utc + 0, hh) || !parseUInt2(utc + 2, mm) || !parseUInt2(utc + 4, ss)) {
+    return;
+  }
+  if (!parseUInt2(date + 0, dd) || !parseUInt2(date + 2, mo) || !parseUInt2(date + 4, yy)) {
+    return;
+  }
+
+  g_gps.utc.hour = hh;
+  g_gps.utc.minute = mm;
+  g_gps.utc.second = ss;
+  g_gps.utc.day = dd;
+  g_gps.utc.month = mo;
+  g_gps.utc.year = (uint16_t)(2000U + yy);
+  g_gps.hasValidUtc = true;
+  g_gps.lastUtcMs = millis();
+
+  double lat = 0.0;
+  double lon = 0.0;
+  if (parseNmeaCoordToDecimal(latRaw, latHem, true, lat) &&
+      parseNmeaCoordToDecimal(lonRaw, lonHem, false, lon)) {
+    g_gps.latitudeDeg = lat;
+    g_gps.longitudeDeg = lon;
+    g_gps.hasValidPosition = true;
+  }
+}
+
+static void processNmeaLine(char* line) {
+  if (!line || line[0] != '$') {
+    return;
+  }
+
+  g_gps.sawAnySentence = true;
+
+  char* star = strchr(line, '*');
+  if (star) {
+    *star = '\0';
+  }
+
+  char* fields[24] = {0};
+  int count = 0;
+  char* saveptr = nullptr;
+  char* tok = strtok_r(line, ",", &saveptr);
+  while (tok && count < 24) {
+    fields[count++] = tok;
+    tok = strtok_r(nullptr, ",", &saveptr);
+  }
+
+  if (count <= 0 || !fields[0]) {
+    return;
+  }
+
+  const char* header = fields[0];
+  size_t n = strlen(header);
+  if (n < 6) {
+    return;
+  }
+
+  const char* type = header + (n - 3);
+  if (strcmp(type, "GGA") == 0) {
+    parseGga(fields, count);
+  } else if (strcmp(type, "GSV") == 0) {
+    parseGsv(fields, count);
+  } else if (strcmp(type, "RMC") == 0) {
+    parseRmc(fields, count);
+  }
+}
+
+static void pollGpsSerial() {
+  while (g_gpsSerial.available() > 0) {
+    char c = (char)g_gpsSerial.read();
+    if (c == '\r') {
+      continue;
+    }
+    if (c == '\n') {
+      if (g_gpsLineLen > 0) {
+        g_gpsLine[g_gpsLineLen] = '\0';
+        processNmeaLine(g_gpsLine);
+        g_gpsLineLen = 0;
+      }
+      continue;
+    }
+
+    if (g_gpsLineLen + 1 < sizeof(g_gpsLine)) {
+      g_gpsLine[g_gpsLineLen++] = c;
+    } else {
+      g_gpsLineLen = 0;
+    }
+  }
+}
+
+static bool collectGpsTraffic(uint32_t windowMs) {
+  uint32_t start = millis();
+  bool sawBytes = false;
+  while ((uint32_t)(millis() - start) < windowMs) {
+    if (g_gpsSerial.available() > 0) {
+      sawBytes = true;
+    }
+    pollGpsSerial();
+    g_sd.update();
+    delay(2);
+  }
+  return sawBytes || g_gps.sawAnySentence;
+}
+
+static void initialGpsProbe() {
+  logf("GPS startup probe at %u baud", (unsigned)GPS_BAUD);
+  (void)collectGpsTraffic(kGpsStartupProbeMs);
+  logf("GPS probe complete: nmea=%s sats_used=%u sats_view=%u utc=%s",
+       g_gps.sawAnySentence ? "yes" : "no",
+       (unsigned)g_gps.satsUsed,
+       (unsigned)g_gps.satsInView,
+       g_gps.hasValidUtc ? "yes" : "no");
+}
+
+static IRAM_ATTR void onPpsEdge() {
+  g_ppsEdgeCount++;
+}
+
+static uint8_t bestSatelliteCount() {
+  return (g_gps.satsUsed > g_gps.satsInView) ? g_gps.satsUsed : g_gps.satsInView;
+}
+
+static bool ensureGpsLogPathReady() {
+  if (!g_sd.isMounted()) {
+    g_gpsPathReady = false;
+    return false;
+  }
+
+  if (g_gpsPathReady) {
+    return true;
+  }
+
+  if (!g_sd.ensureDirRecursive("/gps")) {
+    logf("Could not create /gps directory");
+    return false;
+  }
+
+  // Touch the log file so a clean SD card is prepared before first discipline event.
+  File f = SD.open("/gps/discipline_rtc.log", FILE_APPEND);
+  if (!f) {
+    logf("Could not open /gps/discipline_rtc.log for append");
+    return false;
+  }
+  f.close();
+
+  g_gpsPathReady = true;
+  return true;
+}
+
+static bool appendDisciplineLog(const DateTime& gpsUtc,
+                                bool havePriorRtc,
+                                int64_t rtcMinusGpsSeconds,
+                                uint8_t sats,
+                                uint32_t utcAgeMs,
+                                uint32_t ppsEdges,
+                                char* outTs,
+                                size_t outTsLen) {
+  if (!ensureGpsLogPathReady()) {
+    logf("SD not mounted, skipping append to gps/discipline_rtc.log");
+    return false;
+  }
+
+  File f = SD.open("/gps/discipline_rtc.log", FILE_APPEND);
+  if (!f) {
+    logf("Could not open /gps/discipline_rtc.log for append");
+    return false;
+  }
+
+  char ts[32];
+  formatUtcCompact(gpsUtc, ts, sizeof(ts));
+  if (outTs && outTsLen > 0) {
+    snprintf(outTs, outTsLen, "%s", ts);
+  }
+
+  char drift[40];
+  if (havePriorRtc) {
+    snprintf(drift, sizeof(drift), "%+lld s", (long long)rtcMinusGpsSeconds);
+  } else {
+    snprintf(drift, sizeof(drift), "RTC_unset");
+  }
+
+  char pos[64];
+  if (g_gps.hasValidPosition) {
+    snprintf(pos, sizeof(pos), "lat=%.6f lon=%.6f", g_gps.latitudeDeg, g_gps.longitudeDeg);
+  } else {
+    snprintf(pos, sizeof(pos), "lat=NA lon=NA");
+  }
+
+  char hdop[16];
+  if (g_gps.hdop > 0.0f) {
+    snprintf(hdop, sizeof(hdop), "%.1f", g_gps.hdop);
+  } else {
+    snprintf(hdop, sizeof(hdop), "NA");
+  }
+
+  char alt[16];
+  if (g_gps.hasValidAltitude) {
+    snprintf(alt, sizeof(alt), "%.1f", g_gps.altitudeM);
+  } else {
+    snprintf(alt, sizeof(alt), "NA");
+  }
+
+  char line[320];
+  snprintf(line,
+           sizeof(line),
+           "%s\t set RTC to GPS using 1PPS pulse-per-second discipline\t"
+           "rtc-gps drift=%s; sats=%u; %s; alt_m=%s; hdop=%s; utc_age_ms=%lu; pps_edges=%lu; "
+           "fw_epoch=%lu; fw_build_utc=%s",
+           ts,
+           drift,
+           (unsigned)sats,
+           pos,
+           alt,
+           hdop,
+           (unsigned long)utcAgeMs,
+           (unsigned long)ppsEdges,
+           (unsigned long)FW_BUILD_EPOCH,
+           FW_BUILD_UTC);
+
+  size_t wrote = f.println(line);
+  f.close();
+  if (wrote == 0) {
+    logf("Append write failed: /gps/discipline_rtc.log");
+    return false;
+  }
+  return true;
+}
+
+static bool gpsUtcIsFresh() {
+  if (!g_gps.hasValidUtc) {
+    return false;
+  }
+  return (uint32_t)(millis() - g_gps.lastUtcMs) <= 2000;
+}
+
+static bool waitForNextPps(uint32_t timeoutMs) {
+  uint32_t startCount = g_ppsEdgeCount;
+  uint32_t startMs = millis();
+  while ((uint32_t)(millis() - startMs) < timeoutMs) {
+    pollGpsSerial();
+    g_sd.update();
+    if (g_ppsEdgeCount != startCount) {
+      return true;
+    }
+    delay(2);
+  }
+  return false;
+}
+
+static void waitWithUpdates(uint32_t delayMs) {
+  uint32_t start = millis();
+  while ((uint32_t)(millis() - start) < delayMs) {
+    pollGpsSerial();
+    g_sd.update();
+    delay(10);
+  }
+}
+
+static void showNoTimeAndDelay() {
+  uint8_t sats = bestSatelliteCount();
+  char l3[24];
+  snprintf(l3, sizeof(l3), "Satellites: %u", (unsigned)sats);
+  oledShowLines("GPS time unavailable", "RTC NOT disciplined", l3, "Retry in 30 seconds");
+  logf("GPS UTC unavailable. satellites=%u. Waiting 30 seconds.", (unsigned)sats);
+  waitWithUpdates(kNoTimeDelayMs);
+}
+
+static bool disciplineRtcToGps() {
+  if (!gpsUtcIsFresh()) {
+    showNoTimeAndDelay();
+    return false;
+  }
+
+  DateTime priorRtc{};
+  bool lowV = false;
+  bool havePriorRtc = rtcRead(priorRtc, lowV);
+  if (havePriorRtc && (lowV || !isValidDateTime(priorRtc))) {
+    havePriorRtc = false;
+  }
+
+  DateTime gpsSnap = g_gps.utc;
+  if (!waitForNextPps(kPpsWaitTimeoutMs)) {
+    oledShowLines("GPS 1PPS missing", "RTC NOT disciplined", "Retry in 30 seconds");
+    logf("No 1PPS edge observed within timeout. Waiting 30 seconds.");
+    waitWithUpdates(kNoTimeDelayMs);
+    return false;
+  }
+
+  DateTime target = gpsSnap;
+  addOneSecond(target);
+
+  if (!rtcWrite(target)) {
+    oledShowLines("RTC write failed", "Could not set from GPS");
+    logf("RTC write failed");
+    return false;
+  }
+
+  int64_t driftSec = 0;
+  if (havePriorRtc) {
+    driftSec = toEpochSeconds(priorRtc) - toEpochSeconds(target);
+  }
+
+  uint8_t sats = bestSatelliteCount();
+  uint32_t utcAgeMs = (uint32_t)(millis() - g_gps.lastUtcMs);
+  uint32_t ppsEdges = g_ppsEdgeCount;
+  char tsCompact[32];
+  bool logOk = appendDisciplineLog(target,
+                                   havePriorRtc,
+                                   driftSec,
+                                   sats,
+                                   utcAgeMs,
+                                   ppsEdges,
+                                   tsCompact,
+                                   sizeof(tsCompact));
+
+  char utcLine[36];
+  char driftLine[36];
+  char logLine[36];
+  formatUtcHuman(target, utcLine, sizeof(utcLine));
+  if (havePriorRtc) {
+    snprintf(driftLine, sizeof(driftLine), "rtc-gps drift: %+lld s", (long long)driftSec);
+  } else {
+    snprintf(driftLine, sizeof(driftLine), "rtc-gps drift: RTC_unset");
+  }
+  snprintf(logLine, sizeof(logLine), "Log:%s sats:%u", logOk ? "ok" : "fail", (unsigned)sats);
+
+  oledShowLines("RTC disciplined to GPS", utcLine, driftLine, logLine, tsCompact);
+
+  logf("RTC disciplined to GPS with 1PPS. %s drift=%+llds lowV=%s",
+       utcLine,
+       (long long)driftSec,
+       lowV ? "yes" : "no");
+  return true;
+}
+
+void setup() {
+  Serial.begin(115200);
+  delay(kSerialDelayMs);
+
+  Serial.println("\r\n==================================================");
+  Serial.println("Exercise 11: Set RTC to GPS with 1PPS discipline");
+  Serial.println("==================================================");
+
+  if (!tbeam_supreme::initPmuForPeripherals(g_pmu, &Serial)) {
+    logf("PMU init failed");
+  }
+
+  Wire.begin(OLED_SDA, OLED_SCL);
+  g_oled.setI2CAddress(OLED_ADDR << 1);
+  g_oled.begin();
+  oledShowLines("Exercise 11", "RTC <- GPS (1PPS)", "Booting...");
+
+  SdWatcherConfig sdCfg{};
+  if (!g_sd.begin(sdCfg, nullptr)) {
+    logf("SD startup manager begin() failed");
+  }
+  (void)ensureGpsLogPathReady();
+
+#ifdef GPS_WAKEUP_PIN
+  pinMode(GPS_WAKEUP_PIN, INPUT);
+#endif
+#ifdef GPS_1PPS_PIN
+  pinMode(GPS_1PPS_PIN, INPUT);
+  attachInterrupt(digitalPinToInterrupt(GPS_1PPS_PIN), onPpsEdge, RISING);
+#endif
+
+  g_gpsSerial.setRxBufferSize(1024);
+  g_gpsSerial.begin(GPS_BAUD, SERIAL_8N1, GPS_RX_PIN, GPS_TX_PIN);
+  logf("GPS UART started: RX=%d TX=%d baud=%u", GPS_RX_PIN, GPS_TX_PIN, (unsigned)GPS_BAUD);
+
+  oledShowLines("GPS startup probe", "Checking UTC + 1PPS");
+  initialGpsProbe();
+
+  g_nextDisciplineMs = millis();
+}
+
+void loop() {
+  pollGpsSerial();
+  g_sd.update();
+
+  if (g_sd.consumeMountedEvent()) {
+    g_gpsPathReady = false;
+    (void)ensureGpsLogPathReady();
+  }
+  if (g_sd.consumeRemovedEvent()) {
+    g_gpsPathReady = false;
+  }
+
+  uint32_t now = millis();
+  if ((int32_t)(now - g_nextDisciplineMs) >= 0) {
+    bool ok = disciplineRtcToGps();
+    g_nextDisciplineMs = now + (ok ? kLoopMsDiscipline : kNoTimeDelayMs);
+  }
+
+  delay(5);
+}

exercises/12_FiveTalk/READEME.md

@@ -0,0 +1,20 @@
+
+
+main.cpp needs to be modified to reflect the number of units.  It is a zero-based array, so for 7 possible unite, the value of 6 is used in both lines below:
+
+    #if (NODE_SLOT_INDEX < 0) || (NODE_SLOT_INDEX > 6)
+    #error "NODE_SLOT_INDEX must be 0..6"
+    #endif
+
+
+
+INSERT SCREENSHOT HERE.
+
+To compile and load:
+
+     time pio run -e flo -t upload --upload-port /dev/ttytFLO
+
+To monitor (replace with appropriate unit name) for Exercise 12:
+
+    pio device monitor -d /usr/local/src/microreticulum/microReticulumTbeam/exercises/12_FiveTalk -e flo --port /dev/ttytFLO
+

exercises/12_FiveTalk/lib/startup_sd/StartupSdManager.cpp

@@ -0,0 +1,360 @@
+#include "StartupSdManager.h"
+
+#include <stdarg.h>
+#include "driver/gpio.h"
+
+StartupSdManager::StartupSdManager(Print& serial) : serial_(serial) {}
+
+bool StartupSdManager::begin(const SdWatcherConfig& cfg, SdStatusCallback callback) {
+  cfg_ = cfg;
+  callback_ = callback;
+
+  forceSpiDeselected();
+  dumpSdPins("very-early");
+
+  if (!initPmuForSdPower()) {
+    return false;
+  }
+
+  cycleSdRail();
+  delay(cfg_.startupWarmupMs);
+
+  bool warmMounted = false;
+  for (uint8_t i = 0; i < 3; ++i) {
+    if (mountPreferred(false)) {
+      warmMounted = true;
+      break;
+    }
+    delay(200);
+  }
+
+  // Some cards need a longer power/settle window after cold boot.
+  // Before declaring ABSENT, retry with extended settle and a full scan.
+  if (!warmMounted) {
+    logf("Watcher: startup preferred mount failed, retrying with extended settle");
+    cycleSdRail(400, 1200);
+    delay(cfg_.startupWarmupMs + 1500);
+    warmMounted = mountCardFullScan();
+  }
+
+  if (warmMounted) {
+    setStateMounted();
+  } else {
+    setStateAbsent();
+  }
+  return true;
+}
+
+void StartupSdManager::update() {
+  const uint32_t now = millis();
+  const uint32_t pollInterval =
+      (watchState_ == SdWatchState::MOUNTED) ? cfg_.pollIntervalMountedMs : cfg_.pollIntervalAbsentMs;
+
+  if ((uint32_t)(now - lastPollMs_) < pollInterval) {
+    return;
+  }
+  lastPollMs_ = now;
+
+  if (watchState_ == SdWatchState::MOUNTED) {
+    if (verifyMountedCard()) {
+      presentVotes_ = 0;
+      absentVotes_ = 0;
+      return;
+    }
+
+    if (mountPreferred(false) && verifyMountedCard()) {
+      presentVotes_ = 0;
+      absentVotes_ = 0;
+      return;
+    }
+
+    absentVotes_++;
+    presentVotes_ = 0;
+    if (absentVotes_ >= cfg_.votesToAbsent) {
+      setStateAbsent();
+      absentVotes_ = 0;
+    }
+    return;
+  }
+
+  bool mounted = mountPreferred(false);
+  if (!mounted && (uint32_t)(now - lastFullScanMs_) >= cfg_.fullScanIntervalMs) {
+    lastFullScanMs_ = now;
+    if (cfg_.recoveryRailCycleOnFullScan) {
+      logf("Watcher: recovery rail cycle before full scan");
+      cycleSdRail(cfg_.recoveryRailOffMs, cfg_.recoveryRailOnSettleMs);
+      delay(150);
+    }
+    logf("Watcher: preferred probe failed, running full scan");
+    mounted = mountCardFullScan();
+  }
+
+  if (mounted) {
+    presentVotes_++;
+    absentVotes_ = 0;
+    if (presentVotes_ >= cfg_.votesToPresent) {
+      setStateMounted();
+      presentVotes_ = 0;
+    }
+  } else {
+    absentVotes_++;
+    presentVotes_ = 0;
+    if (absentVotes_ >= cfg_.votesToAbsent) {
+      setStateAbsent();
+      absentVotes_ = 0;
+    }
+  }
+}
+
+bool StartupSdManager::consumeMountedEvent() {
+  bool out = mountedEventPending_;
+  mountedEventPending_ = false;
+  return out;
+}
+
+bool StartupSdManager::consumeRemovedEvent() {
+  bool out = removedEventPending_;
+  removedEventPending_ = false;
+  return out;
+}
+
+void StartupSdManager::logf(const char* fmt, ...) {
+  char msg[196];
+  va_list args;
+  va_start(args, fmt);
+  vsnprintf(msg, sizeof(msg), fmt, args);
+  va_end(args);
+  serial_.printf("[%10lu][%06lu] %s\r\n",
+                 (unsigned long)millis(),
+                 (unsigned long)logSeq_++,
+                 msg);
+}
+
+void StartupSdManager::notify(SdEvent event, const char* message) {
+  if (callback_ != nullptr) {
+    callback_(event, message);
+  }
+}
+
+void StartupSdManager::forceSpiDeselected() {
+  pinMode(tbeam_supreme::sdCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  pinMode(tbeam_supreme::imuCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::imuCs(), HIGH);
+}
+
+void StartupSdManager::dumpSdPins(const char* tag) {
+  if (!cfg_.enablePinDumps) {
+    (void)tag;
+    return;
+  }
+
+  const gpio_num_t cs = (gpio_num_t)tbeam_supreme::sdCs();
+  const gpio_num_t sck = (gpio_num_t)tbeam_supreme::sdSck();
+  const gpio_num_t miso = (gpio_num_t)tbeam_supreme::sdMiso();
+  const gpio_num_t mosi = (gpio_num_t)tbeam_supreme::sdMosi();
+  logf("PINS(%s): CS=%d SCK=%d MISO=%d MOSI=%d",
+       tag, gpio_get_level(cs), gpio_get_level(sck), gpio_get_level(miso), gpio_get_level(mosi));
+}
+
+bool StartupSdManager::initPmuForSdPower() {
+  if (!tbeam_supreme::initPmuForPeripherals(pmu_, &serial_)) {
+    logf("ERROR: PMU init failed");
+    return false;
+  }
+  return true;
+}
+
+void StartupSdManager::cycleSdRail(uint32_t offMs, uint32_t onSettleMs) {
+  if (!cfg_.enableSdRailCycle) {
+    return;
+  }
+  if (!pmu_) {
+    logf("SD rail cycle skipped: pmu=null");
+    return;
+  }
+
+  forceSpiDeselected();
+  pmu_->disablePowerOutput(XPOWERS_BLDO1);
+  delay(offMs);
+  pmu_->setPowerChannelVoltage(XPOWERS_BLDO1, 3300);
+  pmu_->enablePowerOutput(XPOWERS_BLDO1);
+  delay(onSettleMs);
+}
+
+bool StartupSdManager::tryMountWithBus(SPIClass& bus, const char* busName, uint32_t hz, bool verbose) {
+  SD.end();
+  bus.end();
+  delay(10);
+  forceSpiDeselected();
+
+  bus.begin(tbeam_supreme::sdSck(), tbeam_supreme::sdMiso(), tbeam_supreme::sdMosi(), tbeam_supreme::sdCs());
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  delay(2);
+  for (int i = 0; i < 10; i++) {
+    bus.transfer(0xFF);
+  }
+  delay(2);
+
+  if (verbose) {
+    logf("SD: trying bus=%s freq=%lu Hz", busName, (unsigned long)hz);
+  }
+
+  if (!SD.begin(tbeam_supreme::sdCs(), bus, hz)) {
+    if (verbose) {
+      logf("SD: mount failed (possible non-FAT format, power, or bus issue)");
+    }
+    return false;
+  }
+
+  if (SD.cardType() == CARD_NONE) {
+    SD.end();
+    return false;
+  }
+
+  sdSpi_ = &bus;
+  sdBusName_ = busName;
+  sdFreq_ = hz;
+  return true;
+}
+
+bool StartupSdManager::mountPreferred(bool verbose) {
+  return tryMountWithBus(sdSpiH_, "HSPI", 400000, verbose);
+}
+
+bool StartupSdManager::mountCardFullScan() {
+  const uint32_t freqs[] = {400000, 1000000, 4000000, 10000000};
+
+  for (uint8_t i = 0; i < (sizeof(freqs) / sizeof(freqs[0])); ++i) {
+    if (tryMountWithBus(sdSpiH_, "HSPI", freqs[i], true)) {
+      logf("SD: card detected and mounted");
+      return true;
+    }
+  }
+  for (uint8_t i = 0; i < (sizeof(freqs) / sizeof(freqs[0])); ++i) {
+    if (tryMountWithBus(sdSpiF_, "FSPI", freqs[i], true)) {
+      logf("SD: card detected and mounted");
+      return true;
+    }
+  }
+
+  logf("SD: begin() failed on all bus/frequency attempts");
+  return false;
+}
+
+bool StartupSdManager::verifyMountedCard() {
+  File root = SD.open("/", FILE_READ);
+  if (!root) {
+    return false;
+  }
+  root.close();
+  return true;
+}
+
+const char* StartupSdManager::cardTypeToString(uint8_t type) {
+  switch (type) {
+    case CARD_MMC:
+      return "MMC";
+    case CARD_SD:
+      return "SDSC";
+    case CARD_SDHC:
+      return "SDHC/SDXC";
+    default:
+      return "UNKNOWN";
+  }
+}
+
+void StartupSdManager::printCardInfo() {
+  uint8_t cardType = SD.cardType();
+  uint64_t cardSizeMB = SD.cardSize() / (1024ULL * 1024ULL);
+  uint64_t totalMB = SD.totalBytes() / (1024ULL * 1024ULL);
+  uint64_t usedMB = SD.usedBytes() / (1024ULL * 1024ULL);
+
+  logf("SD type: %s", cardTypeToString(cardType));
+  logf("SD size: %llu MB", cardSizeMB);
+  logf("FS total: %llu MB", totalMB);
+  logf("FS used : %llu MB", usedMB);
+  logf("SPI bus: %s @ %lu Hz", sdBusName_, (unsigned long)sdFreq_);
+}
+
+bool StartupSdManager::ensureDirRecursive(const char* path) {
+  String full(path);
+  if (!full.startsWith("/")) {
+    full = "/" + full;
+  }
+
+  int start = 1;
+  while (start > 0 && start < (int)full.length()) {
+    int slash = full.indexOf('/', start);
+    String partial = (slash < 0) ? full : full.substring(0, slash);
+    if (!SD.exists(partial.c_str()) && !SD.mkdir(partial.c_str())) {
+      logf("ERROR: mkdir failed for %s", partial.c_str());
+      return false;
+    }
+    if (slash < 0) {
+      break;
+    }
+    start = slash + 1;
+  }
+
+  return true;
+}
+
+bool StartupSdManager::rewriteFile(const char* path, const char* payload) {
+  if (SD.exists(path) && !SD.remove(path)) {
+    logf("ERROR: failed to erase %s", path);
+    return false;
+  }
+
+  File f = SD.open(path, FILE_WRITE);
+  if (!f) {
+    logf("ERROR: failed to create %s", path);
+    return false;
+  }
+
+  size_t wrote = f.println(payload);
+  f.close();
+  if (wrote == 0) {
+    logf("ERROR: write failed for %s", path);
+    return false;
+  }
+  return true;
+}
+
+void StartupSdManager::permissionsDemo(const char* path) {
+  logf("Permissions demo: FAT has no Unix chmod/chown, use open mode only.");
+  File r = SD.open(path, FILE_READ);
+  if (!r) {
+    logf("Could not open %s as FILE_READ", path);
+    return;
+  }
+  size_t writeInReadMode = r.print("attempt write while opened read-only");
+  if (writeInReadMode == 0) {
+    logf("As expected, FILE_READ write was blocked.");
+  } else {
+    logf("NOTE: FILE_READ write returned %u (unexpected)", (unsigned)writeInReadMode);
+  }
+  r.close();
+}
+
+void StartupSdManager::setStateMounted() {
+  if (watchState_ != SdWatchState::MOUNTED) {
+    logf("EVENT: card inserted/mounted");
+    mountedEventPending_ = true;
+    notify(SdEvent::CARD_MOUNTED, "SD card mounted");
+  }
+  watchState_ = SdWatchState::MOUNTED;
+}
+
+void StartupSdManager::setStateAbsent() {
+  if (watchState_ == SdWatchState::MOUNTED) {
+    logf("EVENT: card removed/unavailable");
+    removedEventPending_ = true;
+    notify(SdEvent::CARD_REMOVED, "SD card removed");
+  } else if (watchState_ != SdWatchState::ABSENT) {
+    logf("EVENT: no card detected");
+    notify(SdEvent::NO_CARD, "Missing SD card or invalid FAT16/FAT32 format");
+  }
+  SD.end();
+  watchState_ = SdWatchState::ABSENT;
+}

exercises/12_FiveTalk/lib/startup_sd/StartupSdManager.h

@@ -0,0 +1,90 @@
+#pragma once
+
+#include <Arduino.h>
+#include <SD.h>
+#include <SPI.h>
+#include <Wire.h>
+#include "tbeam_supreme_adapter.h"
+
+enum class SdWatchState : uint8_t {
+  UNKNOWN = 0,
+  ABSENT,
+  MOUNTED
+};
+
+enum class SdEvent : uint8_t {
+  NO_CARD,
+  CARD_MOUNTED,
+  CARD_REMOVED
+};
+
+using SdStatusCallback = void (*)(SdEvent event, const char* message);
+
+struct SdWatcherConfig {
+  bool enableSdRailCycle = true;
+  bool enablePinDumps = true;
+  bool recoveryRailCycleOnFullScan = true;
+  uint32_t recoveryRailOffMs = 250;
+  uint32_t recoveryRailOnSettleMs = 700;
+  uint32_t startupWarmupMs = 1500;
+  uint32_t pollIntervalAbsentMs = 1000;
+  uint32_t pollIntervalMountedMs = 2000;
+  uint32_t fullScanIntervalMs = 10000;
+  uint8_t votesToPresent = 2;
+  uint8_t votesToAbsent = 5;
+};
+
+class StartupSdManager {
+ public:
+  explicit StartupSdManager(Print& serial = Serial);
+
+  bool begin(const SdWatcherConfig& cfg, SdStatusCallback callback = nullptr);
+  void update();
+
+  bool isMounted() const { return watchState_ == SdWatchState::MOUNTED; }
+  SdWatchState state() const { return watchState_; }
+
+  bool consumeMountedEvent();
+  bool consumeRemovedEvent();
+
+  void printCardInfo();
+  bool ensureDirRecursive(const char* path);
+  bool rewriteFile(const char* path, const char* payload);
+  void permissionsDemo(const char* path);
+
+ private:
+  void logf(const char* fmt, ...);
+  void notify(SdEvent event, const char* message);
+  void forceSpiDeselected();
+  void dumpSdPins(const char* tag);
+  bool initPmuForSdPower();
+  void cycleSdRail(uint32_t offMs = 250, uint32_t onSettleMs = 600);
+  bool tryMountWithBus(SPIClass& bus, const char* busName, uint32_t hz, bool verbose);
+  bool mountPreferred(bool verbose);
+  bool mountCardFullScan();
+  bool verifyMountedCard();
+  const char* cardTypeToString(uint8_t type);
+  void setStateMounted();
+  void setStateAbsent();
+
+  Print& serial_;
+  SdWatcherConfig cfg_{};
+  SdStatusCallback callback_ = nullptr;
+
+  SPIClass sdSpiH_{HSPI};
+  SPIClass sdSpiF_{FSPI};
+  SPIClass* sdSpi_ = nullptr;
+  const char* sdBusName_ = "none";
+  uint32_t sdFreq_ = 0;
+  XPowersLibInterface* pmu_ = nullptr;
+
+  SdWatchState watchState_ = SdWatchState::UNKNOWN;
+  uint8_t presentVotes_ = 0;
+  uint8_t absentVotes_ = 0;
+  uint32_t lastPollMs_ = 0;
+  uint32_t lastFullScanMs_ = 0;
+  uint32_t logSeq_ = 0;
+
+  bool mountedEventPending_ = false;
+  bool removedEventPending_ = false;
+};

exercises/12_FiveTalk/lib/startup_sd/library.json

@@ -0,0 +1,12 @@
+{
+  "name": "startup_sd",
+  "version": "0.1.0",
+  "dependencies": [
+    {
+      "name": "XPowersLib"
+    },
+    {
+      "name": "Wire"
+    }
+  ]
+}

exercises/12_FiveTalk/platformio.ini

@@ -0,0 +1,100 @@
+; 20260219 ChatGPT
+; Exercise 12_FiveTalk
+
+[platformio]
+default_envs = amy
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+monitor_speed = 115200
+extra_scripts = pre:scripts/set_build_epoch.py
+lib_deps =
+  jgromes/RadioLib@^6.6.0
+  lewisxhe/XPowersLib@0.3.3
+  Wire
+  olikraus/U8g2@^2.36.4
+
+build_flags =
+  -I ../../shared/boards
+  -I ../../external/microReticulum_Firmware
+  -D BOARD_MODEL=BOARD_TBEAM_S_V1
+  -D OLED_SDA=17
+  -D OLED_SCL=18
+  -D OLED_ADDR=0x3C
+  -D GPS_RX_PIN=9
+  -D GPS_TX_PIN=8
+  -D GPS_WAKEUP_PIN=7
+  -D GPS_1PPS_PIN=6
+  -D GPS_L76K
+  -D NODE_SLOT_COUNT=7
+  -D LORA_CS=10
+  -D LORA_MOSI=11
+  -D LORA_SCK=12
+  -D LORA_MISO=13
+  -D LORA_RESET=5
+  -D LORA_DIO1=1
+  -D LORA_BUSY=4
+  -D LORA_TCXO_VOLTAGE=1.8
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+
+[env:amy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"Amy\"
+  -D NODE_SHORT=\"A\"
+  -D NODE_SLOT_INDEX=0
+
+[env:bob]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"Bob\"
+  -D NODE_SHORT=\"B\"
+  -D NODE_SLOT_INDEX=1
+
+[env:cy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"Cy\"
+  -D NODE_SHORT=\"C\"
+  -D NODE_SLOT_INDEX=2
+
+[env:dan]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"Dan\"
+  -D NODE_SHORT=\"D\"
+  -D NODE_SLOT_INDEX=3
+
+[env:ed]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"Ed\"
+  -D NODE_SHORT=\"E\"
+  -D NODE_SLOT_INDEX=4
+
+[env:flo]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"Flo\"
+  -D NODE_SHORT=\"F\"
+  -D NODE_SLOT_INDEX=5
+
+[env:guy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"Guy\"
+  -D NODE_SHORT=\"G\"
+  -D NODE_SLOT_INDEX=6
+  -D GPS_UBLOX
+
+

exercises/12_FiveTalk/scripts/set_build_epoch.py

@@ -0,0 +1,12 @@
+import time
+Import("env")
+
+epoch = int(time.time())
+utc_tag = time.strftime("%Y%m%d_%H%M%S_z", time.gmtime(epoch))
+
+env.Append(
+    CPPDEFINES=[
+        ("FW_BUILD_EPOCH", str(epoch)),
+        ("FW_BUILD_UTC", '\\"%s\\"' % utc_tag),
+    ]
+)

exercises/13_SD_Card_Diagnostics/README.md

@@ -0,0 +1,71 @@
+## Exercise 13: SD Card Diagnostics
+
+Dedicated SD hardware + software diagnostics for T-Beam Supreme.
+
+This exercise is meant to isolate SD failures like:
+- card only works after reinsertion,
+- intermittent mount loss,
+- one unit never mounts while others do,
+- possible interconnect / socket / power rail issues.
+
+### What it does
+
+1. Uses the `startup_sd` watcher library from Exercise 12 for continuous card presence monitoring.
+2. Logs PMU telemetry repeatedly:
+   - BLDO1 (SD rail enable state)
+   - VBUS voltage
+   - battery voltage and battery-present flag
+3. Samples SD SPI GPIO logic levels (`CS`, `SCK`, `MISO`, `MOSI`) at runtime.
+4. Runs SPI idle-byte probes on both `HSPI` and `FSPI`.
+5. Runs full mount matrix scans:
+   - buses: `HSPI`, then `FSPI`
+   - frequencies: `400k`, `1M`, `4M`, `10M`
+6. Performs SD file I/O validation when mounted:
+   - append to `/diag/sd_diag_probe.log`
+   - flush
+   - reopen and read back verification token
+7. Every few cycles, power-cycles SD rail (BLDO1) and re-tests mount.
+8. Shows live status on OLED and detailed logs on Serial.
+
+### Build
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e amy
+```
+
+### Upload (using your udev aliases)
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+pio run -e amy -t upload --upload-port /dev/ttytAMY
+```
+
+### Monitor
+
+```bash
+pio device monitor --port /dev/ttytAMY --baud 115200
+```
+
+### Interpreting key log lines
+
+- `Mount OK bus=... hz=...`
+  - SD stack works at that bus/speed.
+- `Mount FAIL ...` on all combos
+  - usually hardware path, socket contact, power rail, interconnect, or card format issue.
+- `SPI probe ... ff=8`
+  - typical idle/pull-up style response.
+- `SPI probe ... zero=8`
+  - suspicious: line stuck low/short or bus contention.
+- `BLDO1=0` while testing
+  - SD rail is off; card cannot function.
+- `I/O FAIL` after mount success
+  - media/filesystem instability or write path issue.
+
+### Practical A/B troubleshooting workflow
+
+1. Use one known-good SD card and test it in a known-good unit and Amy.
+2. Compare whether `Mount OK` appears in both units.
+3. If Amy never gets `Mount OK` but good unit does, suspect Amy hardware path.
+4. Gently flex/reseat board stack while monitoring logs for mount transitions.
+5. If behavior changes with pressure/reseat, interconnect/socket contact is likely root cause.

exercises/13_SD_Card_Diagnostics/lib/startup_sd/StartupSdManager.cpp

@@ -0,0 +1,360 @@
+#include "StartupSdManager.h"
+
+#include <stdarg.h>
+#include "driver/gpio.h"
+
+StartupSdManager::StartupSdManager(Print& serial) : serial_(serial) {}
+
+bool StartupSdManager::begin(const SdWatcherConfig& cfg, SdStatusCallback callback) {
+  cfg_ = cfg;
+  callback_ = callback;
+
+  forceSpiDeselected();
+  dumpSdPins("very-early");
+
+  if (!initPmuForSdPower()) {
+    return false;
+  }
+
+  cycleSdRail();
+  delay(cfg_.startupWarmupMs);
+
+  bool warmMounted = false;
+  for (uint8_t i = 0; i < 3; ++i) {
+    if (mountPreferred(false)) {
+      warmMounted = true;
+      break;
+    }
+    delay(200);
+  }
+
+  // Some cards need a longer power/settle window after cold boot.
+  // Before declaring ABSENT, retry with extended settle and a full scan.
+  if (!warmMounted) {
+    logf("Watcher: startup preferred mount failed, retrying with extended settle");
+    cycleSdRail(400, 1200);
+    delay(cfg_.startupWarmupMs + 1500);
+    warmMounted = mountCardFullScan();
+  }
+
+  if (warmMounted) {
+    setStateMounted();
+  } else {
+    setStateAbsent();
+  }
+  return true;
+}
+
+void StartupSdManager::update() {
+  const uint32_t now = millis();
+  const uint32_t pollInterval =
+      (watchState_ == SdWatchState::MOUNTED) ? cfg_.pollIntervalMountedMs : cfg_.pollIntervalAbsentMs;
+
+  if ((uint32_t)(now - lastPollMs_) < pollInterval) {
+    return;
+  }
+  lastPollMs_ = now;
+
+  if (watchState_ == SdWatchState::MOUNTED) {
+    if (verifyMountedCard()) {
+      presentVotes_ = 0;
+      absentVotes_ = 0;
+      return;
+    }
+
+    if (mountPreferred(false) && verifyMountedCard()) {
+      presentVotes_ = 0;
+      absentVotes_ = 0;
+      return;
+    }
+
+    absentVotes_++;
+    presentVotes_ = 0;
+    if (absentVotes_ >= cfg_.votesToAbsent) {
+      setStateAbsent();
+      absentVotes_ = 0;
+    }
+    return;
+  }
+
+  bool mounted = mountPreferred(false);
+  if (!mounted && (uint32_t)(now - lastFullScanMs_) >= cfg_.fullScanIntervalMs) {
+    lastFullScanMs_ = now;
+    if (cfg_.recoveryRailCycleOnFullScan) {
+      logf("Watcher: recovery rail cycle before full scan");
+      cycleSdRail(cfg_.recoveryRailOffMs, cfg_.recoveryRailOnSettleMs);
+      delay(150);
+    }
+    logf("Watcher: preferred probe failed, running full scan");
+    mounted = mountCardFullScan();
+  }
+
+  if (mounted) {
+    presentVotes_++;
+    absentVotes_ = 0;
+    if (presentVotes_ >= cfg_.votesToPresent) {
+      setStateMounted();
+      presentVotes_ = 0;
+    }
+  } else {
+    absentVotes_++;
+    presentVotes_ = 0;
+    if (absentVotes_ >= cfg_.votesToAbsent) {
+      setStateAbsent();
+      absentVotes_ = 0;
+    }
+  }
+}
+
+bool StartupSdManager::consumeMountedEvent() {
+  bool out = mountedEventPending_;
+  mountedEventPending_ = false;
+  return out;
+}
+
+bool StartupSdManager::consumeRemovedEvent() {
+  bool out = removedEventPending_;
+  removedEventPending_ = false;
+  return out;
+}
+
+void StartupSdManager::logf(const char* fmt, ...) {
+  char msg[196];
+  va_list args;
+  va_start(args, fmt);
+  vsnprintf(msg, sizeof(msg), fmt, args);
+  va_end(args);
+  serial_.printf("[%10lu][%06lu] %s\r\n",
+                 (unsigned long)millis(),
+                 (unsigned long)logSeq_++,
+                 msg);
+}
+
+void StartupSdManager::notify(SdEvent event, const char* message) {
+  if (callback_ != nullptr) {
+    callback_(event, message);
+  }
+}
+
+void StartupSdManager::forceSpiDeselected() {
+  pinMode(tbeam_supreme::sdCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  pinMode(tbeam_supreme::imuCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::imuCs(), HIGH);
+}
+
+void StartupSdManager::dumpSdPins(const char* tag) {
+  if (!cfg_.enablePinDumps) {
+    (void)tag;
+    return;
+  }
+
+  const gpio_num_t cs = (gpio_num_t)tbeam_supreme::sdCs();
+  const gpio_num_t sck = (gpio_num_t)tbeam_supreme::sdSck();
+  const gpio_num_t miso = (gpio_num_t)tbeam_supreme::sdMiso();
+  const gpio_num_t mosi = (gpio_num_t)tbeam_supreme::sdMosi();
+  logf("PINS(%s): CS=%d SCK=%d MISO=%d MOSI=%d",
+       tag, gpio_get_level(cs), gpio_get_level(sck), gpio_get_level(miso), gpio_get_level(mosi));
+}
+
+bool StartupSdManager::initPmuForSdPower() {
+  if (!tbeam_supreme::initPmuForPeripherals(pmu_, &serial_)) {
+    logf("ERROR: PMU init failed");
+    return false;
+  }
+  return true;
+}
+
+void StartupSdManager::cycleSdRail(uint32_t offMs, uint32_t onSettleMs) {
+  if (!cfg_.enableSdRailCycle) {
+    return;
+  }
+  if (!pmu_) {
+    logf("SD rail cycle skipped: pmu=null");
+    return;
+  }
+
+  forceSpiDeselected();
+  pmu_->disablePowerOutput(XPOWERS_BLDO1);
+  delay(offMs);
+  pmu_->setPowerChannelVoltage(XPOWERS_BLDO1, 3300);
+  pmu_->enablePowerOutput(XPOWERS_BLDO1);
+  delay(onSettleMs);
+}
+
+bool StartupSdManager::tryMountWithBus(SPIClass& bus, const char* busName, uint32_t hz, bool verbose) {
+  SD.end();
+  bus.end();
+  delay(10);
+  forceSpiDeselected();
+
+  bus.begin(tbeam_supreme::sdSck(), tbeam_supreme::sdMiso(), tbeam_supreme::sdMosi(), tbeam_supreme::sdCs());
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  delay(2);
+  for (int i = 0; i < 10; i++) {
+    bus.transfer(0xFF);
+  }
+  delay(2);
+
+  if (verbose) {
+    logf("SD: trying bus=%s freq=%lu Hz", busName, (unsigned long)hz);
+  }
+
+  if (!SD.begin(tbeam_supreme::sdCs(), bus, hz)) {
+    if (verbose) {
+      logf("SD: mount failed (possible non-FAT format, power, or bus issue)");
+    }
+    return false;
+  }
+
+  if (SD.cardType() == CARD_NONE) {
+    SD.end();
+    return false;
+  }
+
+  sdSpi_ = &bus;
+  sdBusName_ = busName;
+  sdFreq_ = hz;
+  return true;
+}
+
+bool StartupSdManager::mountPreferred(bool verbose) {
+  return tryMountWithBus(sdSpiH_, "HSPI", 400000, verbose);
+}
+
+bool StartupSdManager::mountCardFullScan() {
+  const uint32_t freqs[] = {400000, 1000000, 4000000, 10000000};
+
+  for (uint8_t i = 0; i < (sizeof(freqs) / sizeof(freqs[0])); ++i) {
+    if (tryMountWithBus(sdSpiH_, "HSPI", freqs[i], true)) {
+      logf("SD: card detected and mounted");
+      return true;
+    }
+  }
+  for (uint8_t i = 0; i < (sizeof(freqs) / sizeof(freqs[0])); ++i) {
+    if (tryMountWithBus(sdSpiF_, "FSPI", freqs[i], true)) {
+      logf("SD: card detected and mounted");
+      return true;
+    }
+  }
+
+  logf("SD: begin() failed on all bus/frequency attempts");
+  return false;
+}
+
+bool StartupSdManager::verifyMountedCard() {
+  File root = SD.open("/", FILE_READ);
+  if (!root) {
+    return false;
+  }
+  root.close();
+  return true;
+}
+
+const char* StartupSdManager::cardTypeToString(uint8_t type) {
+  switch (type) {
+    case CARD_MMC:
+      return "MMC";
+    case CARD_SD:
+      return "SDSC";
+    case CARD_SDHC:
+      return "SDHC/SDXC";
+    default:
+      return "UNKNOWN";
+  }
+}
+
+void StartupSdManager::printCardInfo() {
+  uint8_t cardType = SD.cardType();
+  uint64_t cardSizeMB = SD.cardSize() / (1024ULL * 1024ULL);
+  uint64_t totalMB = SD.totalBytes() / (1024ULL * 1024ULL);
+  uint64_t usedMB = SD.usedBytes() / (1024ULL * 1024ULL);
+
+  logf("SD type: %s", cardTypeToString(cardType));
+  logf("SD size: %llu MB", cardSizeMB);
+  logf("FS total: %llu MB", totalMB);
+  logf("FS used : %llu MB", usedMB);
+  logf("SPI bus: %s @ %lu Hz", sdBusName_, (unsigned long)sdFreq_);
+}
+
+bool StartupSdManager::ensureDirRecursive(const char* path) {
+  String full(path);
+  if (!full.startsWith("/")) {
+    full = "/" + full;
+  }
+
+  int start = 1;
+  while (start > 0 && start < (int)full.length()) {
+    int slash = full.indexOf('/', start);
+    String partial = (slash < 0) ? full : full.substring(0, slash);
+    if (!SD.exists(partial.c_str()) && !SD.mkdir(partial.c_str())) {
+      logf("ERROR: mkdir failed for %s", partial.c_str());
+      return false;
+    }
+    if (slash < 0) {
+      break;
+    }
+    start = slash + 1;
+  }
+
+  return true;
+}
+
+bool StartupSdManager::rewriteFile(const char* path, const char* payload) {
+  if (SD.exists(path) && !SD.remove(path)) {
+    logf("ERROR: failed to erase %s", path);
+    return false;
+  }
+
+  File f = SD.open(path, FILE_WRITE);
+  if (!f) {
+    logf("ERROR: failed to create %s", path);
+    return false;
+  }
+
+  size_t wrote = f.println(payload);
+  f.close();
+  if (wrote == 0) {
+    logf("ERROR: write failed for %s", path);
+    return false;
+  }
+  return true;
+}
+
+void StartupSdManager::permissionsDemo(const char* path) {
+  logf("Permissions demo: FAT has no Unix chmod/chown, use open mode only.");
+  File r = SD.open(path, FILE_READ);
+  if (!r) {
+    logf("Could not open %s as FILE_READ", path);
+    return;
+  }
+  size_t writeInReadMode = r.print("attempt write while opened read-only");
+  if (writeInReadMode == 0) {
+    logf("As expected, FILE_READ write was blocked.");
+  } else {
+    logf("NOTE: FILE_READ write returned %u (unexpected)", (unsigned)writeInReadMode);
+  }
+  r.close();
+}
+
+void StartupSdManager::setStateMounted() {
+  if (watchState_ != SdWatchState::MOUNTED) {
+    logf("EVENT: card inserted/mounted");
+    mountedEventPending_ = true;
+    notify(SdEvent::CARD_MOUNTED, "SD card mounted");
+  }
+  watchState_ = SdWatchState::MOUNTED;
+}
+
+void StartupSdManager::setStateAbsent() {
+  if (watchState_ == SdWatchState::MOUNTED) {
+    logf("EVENT: card removed/unavailable");
+    removedEventPending_ = true;
+    notify(SdEvent::CARD_REMOVED, "SD card removed");
+  } else if (watchState_ != SdWatchState::ABSENT) {
+    logf("EVENT: no card detected");
+    notify(SdEvent::NO_CARD, "Missing SD card or invalid FAT16/FAT32 format");
+  }
+  SD.end();
+  watchState_ = SdWatchState::ABSENT;
+}

exercises/13_SD_Card_Diagnostics/lib/startup_sd/StartupSdManager.h

@@ -0,0 +1,90 @@
+#pragma once
+
+#include <Arduino.h>
+#include <SD.h>
+#include <SPI.h>
+#include <Wire.h>
+#include "tbeam_supreme_adapter.h"
+
+enum class SdWatchState : uint8_t {
+  UNKNOWN = 0,
+  ABSENT,
+  MOUNTED
+};
+
+enum class SdEvent : uint8_t {
+  NO_CARD,
+  CARD_MOUNTED,
+  CARD_REMOVED
+};
+
+using SdStatusCallback = void (*)(SdEvent event, const char* message);
+
+struct SdWatcherConfig {
+  bool enableSdRailCycle = true;
+  bool enablePinDumps = true;
+  bool recoveryRailCycleOnFullScan = true;
+  uint32_t recoveryRailOffMs = 250;
+  uint32_t recoveryRailOnSettleMs = 700;
+  uint32_t startupWarmupMs = 1500;
+  uint32_t pollIntervalAbsentMs = 1000;
+  uint32_t pollIntervalMountedMs = 2000;
+  uint32_t fullScanIntervalMs = 10000;
+  uint8_t votesToPresent = 2;
+  uint8_t votesToAbsent = 5;
+};
+
+class StartupSdManager {
+ public:
+  explicit StartupSdManager(Print& serial = Serial);
+
+  bool begin(const SdWatcherConfig& cfg, SdStatusCallback callback = nullptr);
+  void update();
+
+  bool isMounted() const { return watchState_ == SdWatchState::MOUNTED; }
+  SdWatchState state() const { return watchState_; }
+
+  bool consumeMountedEvent();
+  bool consumeRemovedEvent();
+
+  void printCardInfo();
+  bool ensureDirRecursive(const char* path);
+  bool rewriteFile(const char* path, const char* payload);
+  void permissionsDemo(const char* path);
+
+ private:
+  void logf(const char* fmt, ...);
+  void notify(SdEvent event, const char* message);
+  void forceSpiDeselected();
+  void dumpSdPins(const char* tag);
+  bool initPmuForSdPower();
+  void cycleSdRail(uint32_t offMs = 250, uint32_t onSettleMs = 600);
+  bool tryMountWithBus(SPIClass& bus, const char* busName, uint32_t hz, bool verbose);
+  bool mountPreferred(bool verbose);
+  bool mountCardFullScan();
+  bool verifyMountedCard();
+  const char* cardTypeToString(uint8_t type);
+  void setStateMounted();
+  void setStateAbsent();
+
+  Print& serial_;
+  SdWatcherConfig cfg_{};
+  SdStatusCallback callback_ = nullptr;
+
+  SPIClass sdSpiH_{HSPI};
+  SPIClass sdSpiF_{FSPI};
+  SPIClass* sdSpi_ = nullptr;
+  const char* sdBusName_ = "none";
+  uint32_t sdFreq_ = 0;
+  XPowersLibInterface* pmu_ = nullptr;
+
+  SdWatchState watchState_ = SdWatchState::UNKNOWN;
+  uint8_t presentVotes_ = 0;
+  uint8_t absentVotes_ = 0;
+  uint32_t lastPollMs_ = 0;
+  uint32_t lastFullScanMs_ = 0;
+  uint32_t logSeq_ = 0;
+
+  bool mountedEventPending_ = false;
+  bool removedEventPending_ = false;
+};

exercises/13_SD_Card_Diagnostics/lib/startup_sd/library.json

@@ -0,0 +1,12 @@
+{
+  "name": "startup_sd",
+  "version": "0.1.0",
+  "dependencies": [
+    {
+      "name": "XPowersLib"
+    },
+    {
+      "name": "Wire"
+    }
+  ]
+}

exercises/13_SD_Card_Diagnostics/platformio.ini

@@ -0,0 +1,57 @@
+; 20260219 ChatGPT
+; Exercise 13_SD_Card_Diagnostics
+
+[platformio]
+default_envs = amy
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+monitor_speed = 115200
+extra_scripts = pre:scripts/set_build_epoch.py
+lib_deps =
+  lewisxhe/XPowersLib@0.3.3
+  Wire
+  olikraus/U8g2@^2.36.4
+
+build_flags =
+  -I ../../shared/boards
+  -I ../../external/microReticulum_Firmware
+  -D BOARD_MODEL=BOARD_TBEAM_S_V1
+  -D OLED_SDA=17
+  -D OLED_SCL=18
+  -D OLED_ADDR=0x3C
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+
+[env:amy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"AMY\"
+  -D DIAG_TEST_NOTE=\"clear_holder_disconnected_main_screws_removed_pcb_socket_screw_removed\"
+
+[env:bob]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"BOB\"
+
+[env:cy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"CY\"
+
+[env:dan]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"DAN\"
+
+[env:ed]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"ED\"

exercises/13_SD_Card_Diagnostics/scripts/set_build_epoch.py

@@ -0,0 +1,12 @@
+import time
+Import("env")
+
+epoch = int(time.time())
+utc_tag = time.strftime("%Y%m%d_%H%M%S_z", time.gmtime(epoch))
+
+env.Append(
+    CPPDEFINES=[
+        ("FW_BUILD_EPOCH", str(epoch)),
+        ("FW_BUILD_UTC", '\\"%s\\"' % utc_tag),
+    ]
+)

exercises/13_SD_Card_Diagnostics/src/main.cpp

@@ -0,0 +1,512 @@
+// 20260219 ChatGPT
+// Exercise 13: SD Card Diagnostics
+
+#include <Arduino.h>
+#include <Wire.h>
+#include <SPI.h>
+#include <SD.h>
+#include <U8g2lib.h>
+#include <stdarg.h>
+#include <driver/gpio.h>
+
+#include "StartupSdManager.h"
+#include "tbeam_supreme_adapter.h"
+
+#ifndef NODE_LABEL
+#define NODE_LABEL "DIAG"
+#endif
+
+#ifndef OLED_SDA
+#define OLED_SDA 17
+#endif
+#ifndef OLED_SCL
+#define OLED_SCL 18
+#endif
+#ifndef OLED_ADDR
+#define OLED_ADDR 0x3C
+#endif
+#ifndef FILE_APPEND
+#define FILE_APPEND FILE_WRITE
+#endif
+#ifndef FW_BUILD_UTC
+#define FW_BUILD_UTC "unknown"
+#endif
+#ifndef DIAG_TEST_NOTE
+#define DIAG_TEST_NOTE "enclosure screws removed; board lightly constrained"
+#endif
+
+static const uint32_t kSerialDelayMs = 1500;
+static const uint32_t kLoopDelayMs = 10;
+static const uint32_t kHeartbeatMs = 2000;
+static const uint32_t kDiagCycleMs = 20000;
+static const uint32_t kRailRetestEvery = 3;
+
+static XPowersLibInterface* g_pmu = nullptr;
+static StartupSdManager g_sd(Serial);
+static U8G2_SH1106_128X64_NONAME_F_HW_I2C g_oled(U8G2_R0, U8X8_PIN_NONE);
+static SPIClass g_spiH(HSPI);
+static SPIClass g_spiF(FSPI);
+
+static uint32_t g_logSeq = 0;
+static uint32_t g_lastHeartbeatMs = 0;
+static uint32_t g_lastDiagMs = 0;
+static uint32_t g_diagCycleCount = 0;
+
+static bool g_lastMounted = false;
+static char g_lastDiagLine1[28] = "Diag: waiting";
+static char g_lastDiagLine2[28] = "No cycle yet";
+
+struct PinSnapshot {
+  int cs = -1;
+  int sck = -1;
+  int miso = -1;
+  int mosi = -1;
+};
+
+struct ProbeSummary {
+  uint8_t ffCount = 0;
+  uint8_t zeroCount = 0;
+  uint8_t otherCount = 0;
+  uint8_t firstBytes[8] = {0};
+};
+
+struct MountMatrixResult {
+  bool anySuccess = false;
+  uint8_t attempts = 0;
+  const char* successBus = "none";
+  uint32_t successHz = 0;
+};
+
+static ProbeSummary g_lastProbeH{};
+static ProbeSummary g_lastProbeF{};
+
+static void logf(const char* fmt, ...) {
+  char msg[240];
+  va_list args;
+  va_start(args, fmt);
+  vsnprintf(msg, sizeof(msg), fmt, args);
+  va_end(args);
+  Serial.printf("[%10lu][%06lu] %s\r\n", (unsigned long)millis(), (unsigned long)g_logSeq++, msg);
+}
+
+static void oledShowLines(const char* l1,
+                          const char* l2 = nullptr,
+                          const char* l3 = nullptr,
+                          const char* l4 = nullptr,
+                          const char* l5 = nullptr) {
+  g_oled.clearBuffer();
+  g_oled.setFont(u8g2_font_5x8_tf);
+  if (l1) g_oled.drawUTF8(0, 12, l1);
+  if (l2) g_oled.drawUTF8(0, 24, l2);
+  if (l3) g_oled.drawUTF8(0, 36, l3);
+  if (l4) g_oled.drawUTF8(0, 48, l4);
+  if (l5) g_oled.drawUTF8(0, 60, l5);
+  g_oled.sendBuffer();
+}
+
+static void forceSpiDeselected() {
+  pinMode(tbeam_supreme::sdCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  pinMode(tbeam_supreme::imuCs(), OUTPUT);
+  digitalWrite(tbeam_supreme::imuCs(), HIGH);
+}
+
+static PinSnapshot readPins() {
+  PinSnapshot s;
+  s.cs = gpio_get_level((gpio_num_t)tbeam_supreme::sdCs());
+  s.sck = gpio_get_level((gpio_num_t)tbeam_supreme::sdSck());
+  s.miso = gpio_get_level((gpio_num_t)tbeam_supreme::sdMiso());
+  s.mosi = gpio_get_level((gpio_num_t)tbeam_supreme::sdMosi());
+  return s;
+}
+
+static void logPins(const char* tag) {
+  PinSnapshot p = readPins();
+  logf("PINS(%s): CS=%d SCK=%d MISO=%d MOSI=%d", tag, p.cs, p.sck, p.miso, p.mosi);
+}
+
+static void readPmu(float& vbusV, float& battV, bool& bldo1On, bool& battPresent) {
+  vbusV = -1.0f;
+  battV = -1.0f;
+  bldo1On = false;
+  battPresent = false;
+  if (!g_pmu) return;
+
+  bldo1On = g_pmu->isPowerChannelEnable(XPOWERS_BLDO1);
+  battPresent = g_pmu->isBatteryConnect();
+  vbusV = g_pmu->getVbusVoltage() / 1000.0f;
+  battV = g_pmu->getBattVoltage() / 1000.0f;
+}
+
+static bool cycleSdRail(uint32_t offMs = 300, uint32_t onSettleMs = 900) {
+  if (!g_pmu) {
+    logf("Rail cycle skipped: PMU unavailable");
+    return false;
+  }
+
+  forceSpiDeselected();
+  g_pmu->disablePowerOutput(XPOWERS_BLDO1);
+  delay(offMs);
+  g_pmu->setPowerChannelVoltage(XPOWERS_BLDO1, 3300);
+  g_pmu->enablePowerOutput(XPOWERS_BLDO1);
+  delay(onSettleMs);
+  logf("Rail cycle complete (off=%lums on_settle=%lums)", (unsigned long)offMs, (unsigned long)onSettleMs);
+  return true;
+}
+
+static ProbeSummary runIdleProbeOnBus(SPIClass& bus, const char* busName) {
+  ProbeSummary out;
+
+  SD.end();
+  bus.end();
+  delay(5);
+  forceSpiDeselected();
+
+  bus.begin(tbeam_supreme::sdSck(), tbeam_supreme::sdMiso(), tbeam_supreme::sdMosi(), tbeam_supreme::sdCs());
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  delay(1);
+
+  for (int i = 0; i < 8; ++i) {
+    uint8_t b = bus.transfer(0xFF);
+    out.firstBytes[i] = b;
+    if (b == 0xFF) out.ffCount++;
+    else if (b == 0x00) out.zeroCount++;
+    else out.otherCount++;
+  }
+
+  logf("SPI probe %s: ff=%u zero=%u other=%u bytes=%02X %02X %02X %02X %02X %02X %02X %02X",
+       busName,
+       (unsigned)out.ffCount,
+       (unsigned)out.zeroCount,
+       (unsigned)out.otherCount,
+       out.firstBytes[0],
+       out.firstBytes[1],
+       out.firstBytes[2],
+       out.firstBytes[3],
+       out.firstBytes[4],
+       out.firstBytes[5],
+       out.firstBytes[6],
+       out.firstBytes[7]);
+
+  return out;
+}
+
+static bool tryMount(SPIClass& bus, const char* busName, uint32_t hz) {
+  SD.end();
+  bus.end();
+  delay(5);
+  forceSpiDeselected();
+
+  bus.begin(tbeam_supreme::sdSck(), tbeam_supreme::sdMiso(), tbeam_supreme::sdMosi(), tbeam_supreme::sdCs());
+  digitalWrite(tbeam_supreme::sdCs(), HIGH);
+  delay(1);
+  for (int i = 0; i < 10; ++i) {
+    bus.transfer(0xFF);
+  }
+
+  uint32_t t0 = millis();
+  bool ok = SD.begin(tbeam_supreme::sdCs(), bus, hz);
+  uint32_t dt = millis() - t0;
+  if (!ok) {
+    logf("Mount FAIL bus=%s hz=%lu dt=%lums", busName, (unsigned long)hz, (unsigned long)dt);
+    return false;
+  }
+
+  uint8_t type = SD.cardType();
+  if (type == CARD_NONE) {
+    SD.end();
+    logf("Mount FAIL bus=%s hz=%lu dt=%lums cardType=NONE", busName, (unsigned long)hz, (unsigned long)dt);
+    return false;
+  }
+
+  uint64_t mb = SD.cardSize() / (1024ULL * 1024ULL);
+  logf("Mount OK   bus=%s hz=%lu dt=%lums type=%u size=%lluMB",
+       busName,
+       (unsigned long)hz,
+       (unsigned long)dt,
+       (unsigned)type,
+       mb);
+  return true;
+}
+
+static MountMatrixResult runMountMatrix() {
+  const uint32_t freqs[] = {400000, 1000000, 4000000, 10000000};
+  MountMatrixResult result{};
+
+  for (size_t i = 0; i < (sizeof(freqs) / sizeof(freqs[0])); ++i) {
+    result.attempts++;
+    if (tryMount(g_spiH, "HSPI", freqs[i])) {
+      result.anySuccess = true;
+      result.successBus = "HSPI";
+      result.successHz = freqs[i];
+      return result;
+    }
+  }
+
+  for (size_t i = 0; i < (sizeof(freqs) / sizeof(freqs[0])); ++i) {
+    result.attempts++;
+    if (tryMount(g_spiF, "FSPI", freqs[i])) {
+      result.anySuccess = true;
+      result.successBus = "FSPI";
+      result.successHz = freqs[i];
+      return result;
+    }
+  }
+
+  return result;
+}
+
+static void emitVendorReport(const MountMatrixResult& mm,
+                             const ProbeSummary& ph,
+                             const ProbeSummary& pf,
+                             float vbusV,
+                             float battV,
+                             bool bldo1,
+                             bool battPresent) {
+  logf("REPORT node=%s cycle=%lu fw=%s", NODE_LABEL, (unsigned long)g_diagCycleCount, FW_BUILD_UTC);
+  logf("REPORT test_note=%s", DIAG_TEST_NOTE);
+  logf("REPORT power bldo1=%u vbus=%.3fV batt=%.3fV batt_present=%u",
+       bldo1 ? 1U : 0U,
+       vbusV,
+       battV,
+       battPresent ? 1U : 0U);
+  logf("REPORT spi_probe hspi(ff=%u zero=%u other=%u) fspi(ff=%u zero=%u other=%u)",
+       (unsigned)ph.ffCount,
+       (unsigned)ph.zeroCount,
+       (unsigned)ph.otherCount,
+       (unsigned)pf.ffCount,
+       (unsigned)pf.zeroCount,
+       (unsigned)pf.otherCount);
+  if (mm.anySuccess) {
+    logf("REPORT mount_matrix status=PASS attempts=%u first_success=%s@%luHz",
+         (unsigned)mm.attempts,
+         mm.successBus,
+         (unsigned long)mm.successHz);
+    logf("REPORT verdict=SD interface operational in this cycle");
+    return;
+  }
+
+  logf("REPORT mount_matrix status=FAIL attempts=%u first_success=none",
+       (unsigned)mm.attempts);
+
+  if (bldo1 && vbusV > 4.5f && ph.ffCount == 8 && pf.ffCount == 8) {
+    logf("REPORT verdict=Power looks good; SPI lines idle high; no card response on any bus/frequency; likely socket/interconnect/baseboard hardware fault");
+  } else if (!bldo1) {
+    logf("REPORT verdict=SD rail appears off; investigate PMU/BLDO1 control path");
+  } else {
+    logf("REPORT verdict=No card response; check SD socket, board interconnect, signal integrity, and card seating");
+  }
+}
+
+static bool runFileIoValidation(uint32_t cycleNo) {
+  if (!SD.exists("/diag")) {
+    if (!SD.mkdir("/diag")) {
+      logf("I/O FAIL: cannot create /diag");
+      return false;
+    }
+  }
+
+  const char* path = "/diag/sd_diag_probe.log";
+  File f = SD.open(path, FILE_APPEND);
+  if (!f) {
+    logf("I/O FAIL: cannot open %s", path);
+    return false;
+  }
+
+  float vbusV = 0.0f, battV = 0.0f;
+  bool bldo1 = false, battPresent = false;
+  readPmu(vbusV, battV, bldo1, battPresent);
+
+  uint32_t t0 = millis();
+  f.printf("cycle=%lu ms=%lu bldo1=%u vbus=%.3f batt=%.3f batt_present=%u mounted=%u\n",
+           (unsigned long)cycleNo,
+           (unsigned long)millis(),
+           bldo1 ? 1U : 0U,
+           vbusV,
+           battV,
+           battPresent ? 1U : 0U,
+           g_sd.isMounted() ? 1U : 0U);
+  f.flush();
+  f.close();
+
+  uint32_t writeMs = millis() - t0;
+
+  File r = SD.open(path, FILE_READ);
+  if (!r) {
+    logf("I/O FAIL: reopen for read failed");
+    return false;
+  }
+
+  size_t size = (size_t)r.size();
+  if (size == 0) {
+    r.close();
+    logf("I/O FAIL: file size is zero");
+    return false;
+  }
+
+  r.seek(size > 120 ? size - 120 : 0);
+  String tail = r.readString();
+  r.close();
+
+  if (tail.indexOf(String("cycle=") + cycleNo) < 0) {
+    logf("I/O FAIL: verification token missing for cycle=%lu", (unsigned long)cycleNo);
+    return false;
+  }
+
+  logf("I/O OK: append+flush+readback size=%uB write=%lums", (unsigned)size, (unsigned long)writeMs);
+  return true;
+}
+
+static void onSdEvent(SdEvent event, const char* message) {
+  logf("SD event: %s", message ? message : "(null)");
+
+  if (event == SdEvent::NO_CARD) {
+    oledShowLines("SD Diagnostics", "NO CARD", "Insert/reseat card");
+  } else if (event == SdEvent::CARD_MOUNTED) {
+    oledShowLines("SD Diagnostics", "CARD MOUNTED", "Running checks");
+  } else if (event == SdEvent::CARD_REMOVED) {
+    oledShowLines("SD Diagnostics", "CARD REMOVED", "Check socket/fit");
+  }
+}
+
+static void emitHeartbeat() {
+  float vbusV = 0.0f, battV = 0.0f;
+  bool bldo1 = false, battPresent = false;
+  readPmu(vbusV, battV, bldo1, battPresent);
+
+  PinSnapshot p = readPins();
+  logf("HB mounted=%u BLDO1=%u VBUS=%.3fV VBAT=%.3fV batt_present=%u pins cs=%d sck=%d miso=%d mosi=%d",
+       g_sd.isMounted() ? 1U : 0U,
+       bldo1 ? 1U : 0U,
+       vbusV,
+       battV,
+       battPresent ? 1U : 0U,
+       p.cs,
+       p.sck,
+       p.miso,
+       p.mosi);
+
+  char l1[28], l2[28], l3[28], l4[28], l5[28];
+  snprintf(l1, sizeof(l1), "%s SD DIAG", NODE_LABEL);
+  snprintf(l2, sizeof(l2), "mounted:%s bldo1:%u", g_sd.isMounted() ? "yes" : "no", bldo1 ? 1U : 0U);
+  snprintf(l3, sizeof(l3), "VBUS:%.2f VBAT:%.2f", vbusV, battV);
+  snprintf(l4, sizeof(l4), "MISO:%d CS:%d", p.miso, p.cs);
+  snprintf(l5, sizeof(l5), "%s | %s", g_lastDiagLine1, g_lastDiagLine2);
+  oledShowLines(l1, l2, l3, l4, l5);
+}
+
+static void runDiagnosticCycle() {
+  g_diagCycleCount++;
+  logf("========== DIAG CYCLE %lu START =========", (unsigned long)g_diagCycleCount);
+
+  float vbusV = 0.0f, battV = 0.0f;
+  bool bldo1 = false, battPresent = false;
+  readPmu(vbusV, battV, bldo1, battPresent);
+  logf("Power baseline: BLDO1=%u VBUS=%.3fV VBAT=%.3fV batt_present=%u",
+       bldo1 ? 1U : 0U,
+       vbusV,
+       battV,
+       battPresent ? 1U : 0U);
+
+  logPins("diag-start");
+  g_lastProbeH = runIdleProbeOnBus(g_spiH, "HSPI");
+  g_lastProbeF = runIdleProbeOnBus(g_spiF, "FSPI");
+
+  MountMatrixResult mm = runMountMatrix();
+  if (!mm.anySuccess) {
+    snprintf(g_lastDiagLine1, sizeof(g_lastDiagLine1), "Mount scan: FAIL");
+    snprintf(g_lastDiagLine2, sizeof(g_lastDiagLine2), "No bus/freq worked");
+    SD.end();
+  } else {
+    bool ioOk = runFileIoValidation(g_diagCycleCount);
+    snprintf(g_lastDiagLine1, sizeof(g_lastDiagLine1), "Mount scan: OK");
+    snprintf(g_lastDiagLine2, sizeof(g_lastDiagLine2), "File I/O: %s", ioOk ? "OK" : "FAIL");
+    SD.end();
+  }
+
+  if ((g_diagCycleCount % kRailRetestEvery) == 0) {
+    logf("Rail retest step");
+    if (cycleSdRail()) {
+      MountMatrixResult remount = runMountMatrix();
+      logf("Rail retest remount: %s", remount.anySuccess ? "OK" : "FAIL");
+      SD.end();
+    }
+  }
+
+  emitVendorReport(mm, g_lastProbeH, g_lastProbeF, vbusV, battV, bldo1, battPresent);
+
+  logf("========== DIAG CYCLE %lu END =========", (unsigned long)g_diagCycleCount);
+}
+
+void setup() {
+  Serial.begin(115200);
+  delay(kSerialDelayMs);
+
+  Serial.println("\r\n==================================================");
+  Serial.println("Exercise 13: SD Card Diagnostics");
+  Serial.println("==================================================");
+
+  logf("Node: %s", NODE_LABEL);
+  logf("FW build UTC: %s", FW_BUILD_UTC);
+  logf("Test note: %s", DIAG_TEST_NOTE);
+  logf("Pins: CS=%d SCK=%d MISO=%d MOSI=%d IMU_CS=%d", tbeam_supreme::sdCs(), tbeam_supreme::sdSck(), tbeam_supreme::sdMiso(), tbeam_supreme::sdMosi(), tbeam_supreme::imuCs());
+  logf("PMU I2C: SDA1=%d SCL1=%d", tbeam_supreme::i2cSda(), tbeam_supreme::i2cScl());
+
+  Wire.begin(OLED_SDA, OLED_SCL);
+  g_oled.setI2CAddress(OLED_ADDR << 1);
+  g_oled.begin();
+  oledShowLines("Exercise 13", "SD Card Diagnostics", NODE_LABEL, "Booting...");
+
+  if (!tbeam_supreme::initPmuForPeripherals(g_pmu, &Serial)) {
+    logf("WARN: PMU init failed via adapter");
+  }
+
+  forceSpiDeselected();
+  logPins("boot");
+
+  SdWatcherConfig cfg{};
+  cfg.enableSdRailCycle = true;
+  cfg.enablePinDumps = true;
+  cfg.recoveryRailCycleOnFullScan = true;
+  cfg.startupWarmupMs = 1500;
+  cfg.pollIntervalAbsentMs = 1000;
+  cfg.pollIntervalMountedMs = 2000;
+  cfg.fullScanIntervalMs = 8000;
+  cfg.votesToPresent = 2;
+  cfg.votesToAbsent = 5;
+
+  if (!g_sd.begin(cfg, onSdEvent)) {
+    logf("WARN: StartupSdManager begin() failed");
+  }
+
+  g_lastMounted = g_sd.isMounted();
+  g_lastHeartbeatMs = millis();
+  g_lastDiagMs = millis() - kDiagCycleMs + 2000;
+}
+
+void loop() {
+  g_sd.update();
+
+  if (g_sd.consumeMountedEvent()) {
+    g_lastMounted = true;
+    logf("Event: mounted");
+  }
+  if (g_sd.consumeRemovedEvent()) {
+    g_lastMounted = false;
+    logf("Event: removed");
+  }
+
+  uint32_t now = millis();
+
+  if ((uint32_t)(now - g_lastHeartbeatMs) >= kHeartbeatMs) {
+    g_lastHeartbeatMs = now;
+    emitHeartbeat();
+  }
+
+  if ((uint32_t)(now - g_lastDiagMs) >= kDiagCycleMs) {
+    g_lastDiagMs = now;
+    runDiagnosticCycle();
+  }
+
+  delay(kLoopDelayMs);
+}

exercises/14_Power/README.md

@@ -0,0 +1,30 @@
+# Exercise 14: Power (Charging + Visual)
+
+This exercise is intentionally narrow in scope:
+- Detect if a battery is present.
+- Detect if USB/VBUS power is present.
+- Determine if charging is needed.
+- Keep charging enabled through AXP2101 PMU settings.
+- Flash the PMU charge LED while charging.
+- If fully charged, leave LED off (do nothing).
+
+OLED behavior:
+- For the first 2 minutes after boot, OLED shows:
+  - `Exercise 14 Power`
+  - node name (`NODE_LABEL`)
+  - time (RTC/system time if available, else uptime)
+  - charging state and battery stats
+- After 2 minutes, it switches to a steady `Power Monitor` header while continuing live stats.
+
+## Meshtastic references used
+- `src/Power.cpp`
+  - charging detection path (`isCharging()`, `isVbusIn()`, battery checks)
+- `src/modules/StatusLEDModule.cpp`
+  - PMU charging LED control via `PMU->setChargingLedMode(...)`
+
+## Build and upload
+```bash
+cd /usr/local/src/microreticulum/microReticulumTbeam/exercises/14_Power
+pio run -e ed -t upload
+pio device monitor -b 115200
+```

exercises/14_Power/platformio.ini

@@ -0,0 +1,65 @@
+; 20260220 Codex
+; Exercise 14_Power
+
+[platformio]
+default_envs = ed
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+monitor_speed = 115200
+lib_deps =
+  lewisxhe/XPowersLib@0.3.3
+  Wire
+  olikraus/U8g2@^2.36.4
+
+build_flags =
+  -I ../../shared/boards
+  -I ../../external/microReticulum_Firmware
+  -D BOARD_MODEL=BOARD_TBEAM_S_V1
+  -D OLED_SDA=17
+  -D OLED_SCL=18
+  -D OLED_ADDR=0x3C
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+
+[env:amy]
+extends = env
+upload_port = /dev/ttytAMY
+monitor_port = /dev/ttytAMY
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"AMY\"
+
+[env:bob]
+extends = env
+upload_port = /dev/ttytBOB
+monitor_port = /dev/ttytBOB
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"BOB\"
+
+[env:cy]
+extends = env
+upload_port = /dev/ttytCY
+monitor_port = /dev/ttytCY
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"CY\"
+
+[env:dan]
+extends = env
+upload_port = /dev/ttytDAN
+monitor_port = /dev/ttytDAN
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"DAN\"
+
+[env:ed]
+extends = env
+upload_port = /dev/ttytED
+monitor_port = /dev/ttytED
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"ED\"

exercises/14_Power/src/main.cpp

@@ -0,0 +1,192 @@
+// 20260220 Codex
+// Exercise 14: Power / Charging Visual Indicator
+
+#include <Arduino.h>
+#include <Wire.h>
+#include <U8g2lib.h>
+#include <XPowersLib.h>
+#include <time.h>
+
+#include "tbeam_supreme_adapter.h"
+
+#ifndef NODE_LABEL
+#define NODE_LABEL "POWER"
+#endif
+
+#ifndef OLED_SDA
+#define OLED_SDA 17
+#endif
+#ifndef OLED_SCL
+#define OLED_SCL 18
+#endif
+#ifndef OLED_ADDR
+#define OLED_ADDR 0x3C
+#endif
+
+static XPowersLibInterface *g_pmu = nullptr;
+static U8G2_SH1106_128X64_NONAME_F_HW_I2C g_oled(U8G2_R0, U8X8_PIN_NONE);
+
+static const uint32_t kBlinkIntervalMs = 500;
+static const uint32_t kStatusIntervalMs = 1000;
+static const uint32_t kSerialIntervalMs = 2000;
+static const uint32_t kStartupDisplayMs = 120000;
+
+static bool g_ledOn = false;
+static uint32_t g_lastBlinkMs = 0;
+static uint32_t g_lastStatusMs = 0;
+static uint32_t g_lastSerialMs = 0;
+static uint32_t g_bootMs = 0;
+
+static void oledShow(const char *l1,
+                     const char *l2 = nullptr,
+                     const char *l3 = nullptr,
+                     const char *l4 = nullptr,
+                     const char *l5 = nullptr)
+{
+  g_oled.clearBuffer();
+  g_oled.setFont(u8g2_font_5x8_tf);
+  if (l1) g_oled.drawUTF8(0, 12, l1);
+  if (l2) g_oled.drawUTF8(0, 24, l2);
+  if (l3) g_oled.drawUTF8(0, 36, l3);
+  if (l4) g_oled.drawUTF8(0, 48, l4);
+  if (l5) g_oled.drawUTF8(0, 60, l5);
+  g_oled.sendBuffer();
+}
+
+static void setChargeLed(bool on)
+{
+  if (!g_pmu) return;
+  g_pmu->setChargingLedMode(on ? XPOWERS_CHG_LED_ON : XPOWERS_CHG_LED_OFF);
+}
+
+static void setupChargingDefaults()
+{
+  if (!g_pmu) return;
+  g_pmu->setChargeTargetVoltage(XPOWERS_AXP2101_CHG_VOL_4V2);
+  g_pmu->setChargerConstantCurr(XPOWERS_AXP2101_CHG_CUR_500MA);
+}
+
+static const char *powerState(bool batteryPresent, bool usbPresent, bool fullyCharged, bool chargingNow)
+{
+  if (!batteryPresent) return "NO BATTERY";
+  if (!usbPresent) return "USB NOT PRESENT";
+  if (fullyCharged) return "FULL";
+  if (chargingNow) return "CHARGING";
+  return "IDLE";
+}
+
+static void formatDisplayTime(char *out, size_t outSize)
+{
+  const time_t now = time(nullptr);
+  if (now > 1700000000) {
+    struct tm tmNow;
+    localtime_r(&now, &tmNow);
+    snprintf(out, outSize, "Time: %02d:%02d:%02d", tmNow.tm_hour, tmNow.tm_min, tmNow.tm_sec);
+    return;
+  }
+
+  uint32_t sec = millis() / 1000;
+  uint32_t hh = sec / 3600;
+  uint32_t mm = (sec % 3600) / 60;
+  uint32_t ss = sec % 60;
+  snprintf(out, outSize, "Uptime: %02lu:%02lu:%02lu", (unsigned long)hh, (unsigned long)mm, (unsigned long)ss);
+}
+
+void setup()
+{
+  g_bootMs = millis();
+
+  Serial.begin(115200);
+  delay(1200);
+  Serial.println("Exercise 14_Power boot");
+
+  Wire.begin(OLED_SDA, OLED_SCL);
+  g_oled.setI2CAddress(OLED_ADDR << 1);
+  g_oled.begin();
+  oledShow("Exercise 14 Power", "Node: " NODE_LABEL, "Booting...");
+
+  if (!tbeam_supreme::initPmuForPeripherals(g_pmu, &Serial)) {
+    Serial.println("ERROR: PMU init failed");
+    oledShow("Exercise 14 Power", "Node: " NODE_LABEL, "PMU init FAILED");
+    return;
+  }
+
+  setupChargingDefaults();
+  setChargeLed(false);
+
+  Serial.println("PMU init OK");
+  oledShow("Exercise 14 Power", "Node: " NODE_LABEL, "PMU ready");
+}
+
+void loop()
+{
+  if (!g_pmu) {
+    delay(1000);
+    return;
+  }
+
+  const bool batteryPresent = g_pmu->isBatteryConnect();
+  const bool usbPresent = g_pmu->isVbusIn();
+  const bool chargingNow = g_pmu->isCharging();
+  const int battPercent = g_pmu->getBatteryPercent();
+  const float battV = g_pmu->getBattVoltage() / 1000.0f;
+
+  const bool fullyCharged = batteryPresent && battPercent >= 100;
+  const bool shouldCharge = batteryPresent && usbPresent && !fullyCharged;
+
+  if (shouldCharge) {
+    if (millis() - g_lastBlinkMs >= kBlinkIntervalMs) {
+      g_lastBlinkMs = millis();
+      g_ledOn = !g_ledOn;
+      setChargeLed(g_ledOn);
+    }
+  } else {
+    g_ledOn = false;
+    setChargeLed(false);
+  }
+
+  if (millis() - g_lastStatusMs >= kStatusIntervalMs) {
+    g_lastStatusMs = millis();
+
+    char l1[32];
+    char l2[32];
+    char l3[32];
+    char l4[32];
+    char l5[32];
+
+    const char *state = powerState(batteryPresent, usbPresent, fullyCharged, chargingNow);
+    const bool startupWindow = (millis() - g_bootMs) < kStartupDisplayMs;
+
+    if (startupWindow) {
+      snprintf(l1, sizeof(l1), "Exercise 14 Power");
+    } else {
+      snprintf(l1, sizeof(l1), "Power Monitor");
+    }
+
+    snprintf(l2, sizeof(l2), "Node: %s", NODE_LABEL);
+    formatDisplayTime(l3, sizeof(l3));
+    snprintf(l4, sizeof(l4), "State: %s", state);
+    if (battPercent >= 0) {
+      snprintf(l5, sizeof(l5), "VBAT:%.3fV  %d%%", battV, battPercent);
+    } else {
+      snprintf(l5, sizeof(l5), "VBAT:%.3fV  pct:?", battV);
+    }
+
+    oledShow(l1, l2, l3, l4, l5);
+  }
+
+  if (millis() - g_lastSerialMs >= kSerialIntervalMs) {
+    g_lastSerialMs = millis();
+    Serial.printf("node=%s usb=%u batt=%u charging=%u full=%u led=%u vbatt=%.3fV pct=%d\r\n",
+                  NODE_LABEL,
+                  usbPresent ? 1 : 0,
+                  batteryPresent ? 1 : 0,
+                  chargingNow ? 1 : 0,
+                  fullyCharged ? 1 : 0,
+                  g_ledOn ? 1 : 0,
+                  battV,
+                  battPercent);
+  }
+
+  delay(20);
+}

exercises/15_RAM/README.md

@@ -0,0 +1,16 @@
+# Exercise 15: RAM
+
+This exercise shows available RAM on the console and on the OLED display on a T-Beam Supreme.
+
+Behavior:
+- Reports heap statistics every second over serial.
+- Shows live heap status on the OLED display.
+- Designed as the first step toward volatile /tmp RAM-backed storage.
+
+Build and upload:
+
+```bash
+cd /usr/local/src/microreticulum/microReticulumTbeam/exercises/15_RAM
+pio run -e amy -t upload
+pio device monitor -b 115200
+```

exercises/15_RAM/platformio.ini

@@ -0,0 +1,55 @@
+; 20260403 ChatGPT
+; Exercise 15_RAM
+
+[platformio]
+default_envs = amy
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+monitor_speed = 115200
+extra_scripts = pre:scripts/set_build_epoch.py
+lib_deps =
+  Wire
+  olikraus/U8g2@^2.36.4
+
+build_flags =
+  -I ../../shared/boards
+  -I ../../external/microReticulum_Firmware
+  -D BOARD_MODEL=BOARD_TBEAM_S_V1
+  -D OLED_SDA=17
+  -D OLED_SCL=18
+  -D OLED_ADDR=0x3C
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+
+[env:amy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"AMY\"
+
+[env:bob]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"BOB\"
+
+[env:cy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"CY\"
+
+[env:dan]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"DAN\"
+
+[env:ed]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"ED\"

exercises/15_RAM/scripts/set_build_epoch.py

@@ -0,0 +1,12 @@
+import time
+Import("env")
+
+epoch = int(time.time())
+utc_tag = time.strftime("%Y%m%d_%H%M%S_z", time.gmtime(epoch))
+
+env.Append(
+    CPPDEFINES=[
+        ("FW_BUILD_EPOCH", str(epoch)),
+        ("FW_BUILD_UTC", '\\"%s\\"' % utc_tag),
+    ]
+)

exercises/15_RAM/src/main.cpp

@@ -0,0 +1,272 @@
+// 20260403 ChatGPT
+// Exercise 15_RAM
+
+#include <Arduino.h>
+#include <Wire.h>
+#include <U8g2lib.h>
+#include <time.h>
+
+#ifndef NODE_LABEL
+#define NODE_LABEL "RAM"
+#endif
+
+#ifndef OLED_SDA
+#define OLED_SDA 17
+#endif
+#ifndef OLED_SCL
+#define OLED_SCL 18
+#endif
+#ifndef OLED_ADDR
+#define OLED_ADDR 0x3C
+#endif
+
+static U8G2_SH1106_128X64_NONAME_F_HW_I2C g_oled(U8G2_R0, U8X8_PIN_NONE);
+
+static const char *kTmpPath = "/tmp/AMY_output.log";
+static const size_t kTmpFileCapacity = 32768;
+static char g_tmpFileBuffer[kTmpFileCapacity];
+static size_t g_tmpFileSize = 0;
+static unsigned g_tmpLineNumber = 0;
+
+static void oledShowLines(const char *l1,
+                          const char *l2 = nullptr,
+                          const char *l3 = nullptr,
+                          const char *l4 = nullptr,
+                          const char *l5 = nullptr)
+{
+  g_oled.clearBuffer();
+  g_oled.setFont(u8g2_font_5x8_tf);
+  if (l1) g_oled.drawUTF8(0, 12, l1);
+  if (l2) g_oled.drawUTF8(0, 24, l2);
+  if (l3) g_oled.drawUTF8(0, 36, l3);
+  if (l4) g_oled.drawUTF8(0, 48, l4);
+  if (l5) g_oled.drawUTF8(0, 60, l5);
+  g_oled.sendBuffer();
+}
+
+static size_t getAvailableRamBytes()
+{
+  return ESP.getFreeHeap();
+}
+
+static void getTimestamp(char *out, size_t outSize)
+{
+  const time_t now = time(nullptr);
+  if (now > 1700000000) {
+    struct tm tmNow;
+    localtime_r(&now, &tmNow);
+    snprintf(out, outSize, "%04d-%02d-%02d %02d:%02d:%02d",
+             tmNow.tm_year + 1900,
+             tmNow.tm_mon + 1,
+             tmNow.tm_mday,
+             tmNow.tm_hour,
+             tmNow.tm_min,
+             tmNow.tm_sec);
+    return;
+  }
+
+  const uint32_t sec = millis() / 1000;
+  const uint32_t hh = sec / 3600;
+  const uint32_t mm = (sec % 3600) / 60;
+  const uint32_t ss = sec % 60;
+  snprintf(out, outSize, "uptime %02u:%02u:%02u", (unsigned)hh, (unsigned)mm, (unsigned)ss);
+}
+
+static void appendTimestampLine()
+{
+  char timestamp[32];
+  getTimestamp(timestamp, sizeof(timestamp));
+
+  char line[96];
+  const int written = snprintf(line, sizeof(line), "%u, %s\r\n", g_tmpLineNumber + 1, timestamp);
+  if (written <= 0) {
+    return;
+  }
+
+  const size_t lineLen = (size_t)written;
+  if (g_tmpFileSize + lineLen > kTmpFileCapacity - 1) {
+    Serial.println("Warning: /tmp log full, stopping writes");
+    return;
+  }
+
+  memcpy(g_tmpFileBuffer + g_tmpFileSize, line, lineLen);
+  g_tmpFileSize += lineLen;
+  g_tmpLineNumber++;
+}
+
+static void printRamStatus()
+{
+  const size_t freeBytes = getAvailableRamBytes();
+  const size_t totalBytes = ESP.getHeapSize();
+  const size_t maxAlloc = ESP.getMaxAllocHeap();
+
+  Serial.printf("RAM  total=%u free=%u maxAlloc=%u\r\n", (unsigned)totalBytes, (unsigned)freeBytes, (unsigned)maxAlloc);
+
+  char line1[32];
+  char line2[32];
+  char line3[32];
+
+  snprintf(line1, sizeof(line1), "Exercise 15 RAM");
+  snprintf(line2, sizeof(line2), "Node: %s", NODE_LABEL);
+  snprintf(line3, sizeof(line3), "Free: %u KB", (unsigned)(freeBytes / 1024U));
+  char line4[32];
+  snprintf(line4, sizeof(line4), "Total: %u KB", (unsigned)(totalBytes / 1024U));
+  char line5[32];
+  snprintf(line5, sizeof(line5), "Lines: %u", (unsigned)g_tmpLineNumber);
+
+  oledShowLines(line1, line2, line3, line4, line5);
+}
+
+static void showHelp()
+{
+  Serial.println("RAM command list:");
+  Serial.println("  help           - show this menu");
+  Serial.println("  stat           - show /tmp file state");
+  Serial.println("  read           - read /tmp contents");
+  Serial.println("  clear          - clear /tmp contents");
+  Serial.println("  write <text>   - write text to /tmp");
+  Serial.println("  append <text>  - append text to /tmp");
+}
+
+static void printTmpFileStat()
+{
+  Serial.printf("Path: %s\r\n", kTmpPath);
+  Serial.printf("Size: %u bytes\r\n", (unsigned)g_tmpFileSize);
+  Serial.printf("Lines: %u\r\n", (unsigned)g_tmpLineNumber);
+  Serial.printf("Capacity: %u bytes\r\n", (unsigned)kTmpFileCapacity);
+}
+
+static void printTmpFileContents()
+{
+  if (g_tmpFileSize == 0) {
+    Serial.println("/tmp file is empty");
+    return;
+  }
+
+  Serial.print("/tmp contents: ");
+  Serial.write((const uint8_t *)g_tmpFileBuffer, g_tmpFileSize);
+  if (g_tmpFileBuffer[g_tmpFileSize - 1] != '\n')
+    Serial.println();
+}
+
+static void setTmpFileContent(const char *text)
+{
+  if (!text) {
+    g_tmpFileSize = 0;
+    return;
+  }
+  const size_t newLen = strlen(text);
+  if (newLen > kTmpFileCapacity - 1) {
+    Serial.printf("Error: content too large (%u/%u)\r\n", (unsigned)newLen, (unsigned)kTmpFileCapacity);
+    return;
+  }
+  memcpy(g_tmpFileBuffer, text, newLen);
+  g_tmpFileSize = newLen;
+}
+
+static void appendTmpFileContent(const char *text)
+{
+  if (!text || text[0] == '\0') return;
+  const size_t textLen = strlen(text);
+  if (g_tmpFileSize + textLen > kTmpFileCapacity - 1) {
+    Serial.printf("Error: append would exceed %u bytes\r\n", (unsigned)kTmpFileCapacity);
+    return;
+  }
+  memcpy(g_tmpFileBuffer + g_tmpFileSize, text, textLen);
+  g_tmpFileSize += textLen;
+}
+
+static void processSerialCommand(const char *line)
+{
+  if (!line || line[0] == '\0') return;
+
+  char tmp[384];
+  strncpy(tmp, line, sizeof(tmp) - 1);
+  tmp[sizeof(tmp) - 1] = '\0';
+
+  char *cmd = strtok(tmp, " \t\r\n");
+  if (!cmd) return;
+
+  if (strcasecmp(cmd, "help") == 0) {
+    showHelp();
+    return;
+  }
+
+  if (strcasecmp(cmd, "stat") == 0) {
+    printTmpFileStat();
+    return;
+  }
+
+  if (strcasecmp(cmd, "read") == 0) {
+    printTmpFileContents();
+    return;
+  }
+
+  if (strcasecmp(cmd, "clear") == 0) {
+    g_tmpFileSize = 0;
+    Serial.println("/tmp cleared");
+    return;
+  }
+
+  if (strcasecmp(cmd, "write") == 0 || strcasecmp(cmd, "append") == 0) {
+    const char *payload = line + strlen(cmd);
+    while (*payload == ' ' || *payload == '\t') payload++;
+    if (strcasecmp(cmd, "write") == 0)
+      setTmpFileContent(payload);
+    else
+      appendTmpFileContent(payload);
+
+    Serial.printf("%s: %u bytes\r\n", cmd,
+                  (unsigned)g_tmpFileSize);
+    return;
+  }
+
+  Serial.println("Unknown command (help for list)");
+}
+
+void setup()
+{
+  Serial.begin(115200);
+  delay(800);
+  Serial.println("Exercise 15_RAM boot");
+
+  Wire.begin(OLED_SDA, OLED_SCL);
+  g_oled.setI2CAddress(OLED_ADDR << 1);
+  g_oled.begin();
+  oledShowLines("Exercise 15_RAM", "Node: " NODE_LABEL, "Booting...");
+
+  delay(1000);
+}
+
+void loop()
+{
+  static uint32_t lastMs = 0;
+  const uint32_t now = millis();
+
+  // check serial commands at all times
+  static char rxLine[384];
+  static size_t rxLen = 0;
+
+  while (Serial.available()) {
+    int c = Serial.read();
+    if (c <= 0) continue;
+    if (c == '\r' || c == '\n') {
+      if (rxLen > 0) {
+        rxLine[rxLen] = '\0';
+        processSerialCommand(rxLine);
+        rxLen = 0;
+      }
+    } else if (rxLen + 1 < sizeof(rxLine)) {
+      rxLine[rxLen++] = (char)c;
+    }
+  }
+
+  if (now - lastMs < 1000) {
+    delay(10);
+    return;
+  }
+  lastMs = now;
+
+  appendTimestampLine();
+  printRamStatus();
+}

exercises/16_PSRAM/README.md

@@ -0,0 +1,32 @@
+# Exercise 16: PSRAM
+
+This exercise demonstrates usage of PSRAM (Pseudo SRAM) on an ESP32-S3 board, alongside regular RAM metrics.
+
+Behavior:
+- Reports heap and PSRAM statistics every second over serial.
+- Shows live heap and PSRAM status on the OLED display (both on same line).
+- Allows you to write/append/read/clear data in a PSRAM-backed buffer (up to ~2MB).
+- Designed as an extension of Exercise 15_RAM to explore larger volatile storage.
+
+Note: the exercise now targets a PSRAM-enabled ESP32-S3 board definition (`freenove_esp32_s3_wroom`). This board profile has 8MB flash + 8MB PSRAM, matching the T-Beam Supreme specifications. If your hardware differs, adjust accordingly.
+
+Sources:
+- LilyGo T-Beam SUPREME datasheet/wiki: https://wiki.lilygo.cc/get_started/en/LoRa_GPS/T-Beam-SUPREME/T-Beam-SUPREME.html
+- PlatformIO board definition: https://docs.platformio.org/page/boards/espressif32/freenove_esp32_s3_wroom.html
+- Local PlatformIO board metadata: ~/.platformio/platforms/espressif32/boards/freenove_esp32_s3_wroom.json
+
+Build and upload:
+
+```bash
+cd /usr/local/src/microreticulum/microReticulumTbeam/exercises/16_PSRAM
+pio run -e amy -t upload
+pio device monitor -b 115200
+```
+
+Commands:
+- `help` - show command menu
+- `stat` - show PSRAM buffer state
+- `read` - read PSRAM buffer contents
+- `clear` - clear PSRAM buffer
+- `write <text>` - write text to PSRAM buffer
+- `append <text>` - append text to PSRAM buffer

exercises/16_PSRAM/platformio.ini

@@ -0,0 +1,54 @@
+; 20260403 ChatGPT
+; Exercise 16_PSRAM
+
+[platformio]
+default_envs = amy
+
+[env]
+platform = espressif32
+framework = arduino
+board = freenove_esp32_s3_wroom
+monitor_speed = 115200
+extra_scripts = pre:scripts/set_build_epoch.py
+lib_deps =
+  Wire
+  olikraus/U8g2@^2.36.4
+
+build_flags =
+  -I ../../shared/boards
+  -I ../../external/microReticulum_Firmware
+  -D BOARD_MODEL=BOARD_TBEAM_S_V1
+  -D OLED_SDA=17
+  -D OLED_SCL=18
+  -D OLED_ADDR=0x3C
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+
+board_build.flash_mode = qio
+board_build.psram = 1
+board_build.psram_type = spi
+board_build.arduino.memory_type = qio_qspi
+
+[env:amy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"AMY\"
+
+[env:bob]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"BOB\"
+
+[env:cy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"CY\"
+
+[env:dan]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"DAN\"

exercises/16_PSRAM/scripts/set_build_epoch.py

@@ -0,0 +1,12 @@
+import time
+Import("env")
+
+epoch = int(time.time())
+utc_tag = time.strftime("%Y%m%d_%H%M%S_z", time.gmtime(epoch))
+
+env.Append(
+    CPPDEFINES=[
+        ("FW_BUILD_EPOCH", str(epoch)),
+        ("FW_BUILD_UTC", '\\"%s\\"' % utc_tag),
+    ]
+)

exercises/16_PSRAM/src/main.cpp

@@ -0,0 +1,342 @@
+// 20260403 ChatGPT
+// Exercise 16_PSRAM - Extended Exercise 15_RAM with PSRAM support
+
+#include <Arduino.h>
+#include <Wire.h>
+#include <U8g2lib.h>
+#include <time.h>
+#include <esp_heap_caps.h>
+
+#ifndef NODE_LABEL
+#define NODE_LABEL "PSRAM"
+#endif
+
+#ifndef OLED_SDA
+#define OLED_SDA 17
+#endif
+#ifndef OLED_SCL
+#define OLED_SCL 18
+#endif
+#ifndef OLED_ADDR
+#define OLED_ADDR 0x3C
+#endif
+
+static U8G2_SH1106_128X64_NONAME_F_HW_I2C g_oled(U8G2_R0, U8X8_PIN_NONE);
+
+static const size_t kTmpFileCapacity = 2097152; // 2MB in PSRAM
+static char *g_tmpFileBuffer = nullptr;
+static size_t g_tmpFileSize = 0;
+static unsigned g_tmpLineNumber = 0;
+
+static void oledShowLines(const char *l1,
+                          const char *l2 = nullptr,
+                          const char *l3 = nullptr,
+                          const char *l4 = nullptr,
+                          const char *l5 = nullptr)
+{
+  g_oled.clearBuffer();
+  g_oled.setFont(u8g2_font_5x8_tf);
+  if (l1) g_oled.drawUTF8(0, 12, l1);
+  if (l2) g_oled.drawUTF8(0, 24, l2);
+  if (l3) g_oled.drawUTF8(0, 36, l3);
+  if (l4) g_oled.drawUTF8(0, 48, l4);
+  if (l5) g_oled.drawUTF8(0, 60, l5);
+  g_oled.sendBuffer();
+}
+
+static size_t getAvailableRamBytes()
+{
+  return ESP.getFreeHeap();
+}
+
+static size_t getTotalRamBytes()
+{
+  return ESP.getHeapSize();
+}
+
+static size_t getPSRAMFreeBytes()
+{
+  size_t freeBytes = heap_caps_get_free_size(MALLOC_CAP_SPIRAM);
+  if (freeBytes == 0 && ESP.getFreePsram() > 0) {
+    freeBytes = ESP.getFreePsram();
+  }
+  return freeBytes;
+}
+
+static size_t getPSRAMTotalBytes()
+{
+  size_t totalBytes = heap_caps_get_total_size(MALLOC_CAP_SPIRAM);
+  if (totalBytes == 0 && ESP.getPsramSize() > 0) {
+    totalBytes = ESP.getPsramSize();
+  }
+  return totalBytes;
+}
+
+static void getTimestamp(char *out, size_t outSize)
+{
+  const time_t now = time(nullptr);
+  if (now > 1700000000) {
+    struct tm tmNow;
+    localtime_r(&now, &tmNow);
+    snprintf(out, outSize, "%04d-%02d-%02d %02d:%02d:%02d",
+             tmNow.tm_year + 1900,
+             tmNow.tm_mon + 1,
+             tmNow.tm_mday,
+             tmNow.tm_hour,
+             tmNow.tm_min,
+             tmNow.tm_sec);
+    return;
+  }
+
+  const uint32_t sec = millis() / 1000;
+  const uint32_t hh = sec / 3600;
+  const uint32_t mm = (sec % 3600) / 60;
+  const uint32_t ss = sec % 60;
+  snprintf(out, outSize, "uptime %02u:%02u:%02u", (unsigned)hh, (unsigned)mm, (unsigned)ss);
+}
+
+static void appendTimestampLine()
+{
+  if (!g_tmpFileBuffer) return;
+
+  char timestamp[32];
+  getTimestamp(timestamp, sizeof(timestamp));
+
+  char line[96];
+  const int written = snprintf(line, sizeof(line), "%u, %s\r\n", g_tmpLineNumber + 1, timestamp);
+  if (written <= 0) {
+    return;
+  }
+
+  const size_t lineLen = (size_t)written;
+  if (g_tmpFileSize + lineLen > kTmpFileCapacity - 1) {
+    Serial.println("Warning: PSRAM log full, stopping writes");
+    return;
+  }
+
+  memcpy(g_tmpFileBuffer + g_tmpFileSize, line, lineLen);
+  g_tmpFileSize += lineLen;
+  g_tmpLineNumber++;
+}
+
+static void printRamStatus()
+{
+  const size_t freeRam = getAvailableRamBytes();
+  const size_t totalRam = getTotalRamBytes();
+  const size_t maxAllocRam = ESP.getMaxAllocHeap();
+  
+  const size_t freePSRAM = getPSRAMFreeBytes();
+  const size_t totalPSRAM = getPSRAMTotalBytes();
+
+  Serial.printf("RAM  total=%u free=%u maxAlloc=%u | PSRAM total=%u free=%u\r\n", 
+    (unsigned)totalRam, (unsigned)freeRam, (unsigned)maxAllocRam,
+    (unsigned)totalPSRAM, (unsigned)freePSRAM);
+
+  char line1[32];
+  char line2[32];
+  char line3[32];
+  char line4[32];
+  char line5[32];
+
+  snprintf(line1, sizeof(line1), "Exercise 16 PSRAM");
+  snprintf(line2, sizeof(line2), "Node: %s", NODE_LABEL);
+  
+  // Display format: "Free XXXKb/8.0Mbs"
+  const float psramMb = totalPSRAM / (1024.0f * 1024.0f);
+  const size_t ramKb = freeRam / 1024U;
+  snprintf(line3, sizeof(line3), "Free %uKb/%.1fMbs", (unsigned)ramKb, psramMb);
+  
+  snprintf(line4, sizeof(line4), "PSRAM: %u KB", (unsigned)(freePSRAM / 1024U));
+  snprintf(line5, sizeof(line5), "Lines: %u", (unsigned)g_tmpLineNumber);
+
+  oledShowLines(line1, line2, line3, line4, line5);
+}
+
+static void showHelp()
+{
+  Serial.println("PSRAM command list:");
+  Serial.println("  help           - show this menu");
+  Serial.println("  stat           - show PSRAM buffer state");
+  Serial.println("  read           - read PSRAM buffer contents");
+  Serial.println("  clear          - clear PSRAM buffer contents");
+  Serial.println("  write <text>   - write text to PSRAM buffer");
+  Serial.println("  append <text>  - append text to PSRAM buffer");
+}
+
+static void printPSRAMFileStat()
+{
+  Serial.printf("PSRAM Buffer Capacity: %u bytes\r\n", (unsigned)kTmpFileCapacity);
+  Serial.printf("Current Size: %u bytes\r\n", (unsigned)g_tmpFileSize);
+  Serial.printf("Lines: %u\r\n", (unsigned)g_tmpLineNumber);
+  Serial.printf("PSRAM Total: %u bytes (%.2f MB)\r\n", (unsigned)getPSRAMTotalBytes(), 
+    getPSRAMTotalBytes() / (1024.0f * 1024.0f));
+  Serial.printf("PSRAM Free: %u bytes\r\n", (unsigned)getPSRAMFreeBytes());
+}
+
+static void printPSRAMFileContents()
+{
+  if (!g_tmpFileBuffer) {
+    Serial.println("PSRAM buffer not allocated");
+    return;
+  }
+
+  if (g_tmpFileSize == 0) {
+    Serial.println("PSRAM buffer is empty");
+    return;
+  }
+
+  Serial.print("PSRAM contents: ");
+  Serial.write((const uint8_t *)g_tmpFileBuffer, g_tmpFileSize);
+  if (g_tmpFileBuffer[g_tmpFileSize - 1] != '\n')
+    Serial.println();
+}
+
+static void setPSRAMFileContent(const char *text)
+{
+  if (!g_tmpFileBuffer) {
+    Serial.println("Error: PSRAM buffer not allocated");
+    return;
+  }
+
+  if (!text) {
+    g_tmpFileSize = 0;
+    g_tmpLineNumber = 0;
+    return;
+  }
+  const size_t newLen = strlen(text);
+  if (newLen > kTmpFileCapacity - 1) {
+    Serial.printf("Error: content too large (%u/%u)\r\n", (unsigned)newLen, (unsigned)kTmpFileCapacity);
+    return;
+  }
+  memcpy(g_tmpFileBuffer, text, newLen);
+  g_tmpFileSize = newLen;
+  g_tmpLineNumber = 0;
+}
+
+static void appendPSRAMFileContent(const char *text)
+{
+  if (!g_tmpFileBuffer) {
+    Serial.println("Error: PSRAM buffer not allocated");
+    return;
+  }
+
+  if (!text || text[0] == '\0') return;
+  const size_t textLen = strlen(text);
+  if (g_tmpFileSize + textLen > kTmpFileCapacity - 1) {
+    Serial.printf("Error: append would exceed %u bytes\r\n", (unsigned)kTmpFileCapacity);
+    return;
+  }
+  memcpy(g_tmpFileBuffer + g_tmpFileSize, text, textLen);
+  g_tmpFileSize += textLen;
+}
+
+static void processSerialCommand(const char *line)
+{
+  if (!line || line[0] == '\0') return;
+
+  char tmp[384];
+  strncpy(tmp, line, sizeof(tmp) - 1);
+  tmp[sizeof(tmp) - 1] = '\0';
+
+  char *cmd = strtok(tmp, " \t\r\n");
+  if (!cmd) return;
+
+  if (strcasecmp(cmd, "help") == 0) {
+    showHelp();
+    return;
+  }
+
+  if (strcasecmp(cmd, "stat") == 0) {
+    printPSRAMFileStat();
+    return;
+  }
+
+  if (strcasecmp(cmd, "read") == 0) {
+    printPSRAMFileContents();
+    return;
+  }
+
+  if (strcasecmp(cmd, "clear") == 0) {
+    g_tmpFileSize = 0;
+    g_tmpLineNumber = 0;
+    Serial.println("PSRAM buffer cleared");
+    return;
+  }
+
+  if (strcasecmp(cmd, "write") == 0 || strcasecmp(cmd, "append") == 0) {
+    const char *payload = line + strlen(cmd);
+    while (*payload == ' ' || *payload == '\t') payload++;
+    if (strcasecmp(cmd, "write") == 0)
+      setPSRAMFileContent(payload);
+    else
+      appendPSRAMFileContent(payload);
+
+    Serial.printf("%s: %u bytes\r\n", cmd,
+                  (unsigned)g_tmpFileSize);
+    return;
+  }
+
+  Serial.println("Unknown command (help for list)");
+}
+
+void setup()
+{
+  Serial.begin(115200);
+  delay(800);
+  Serial.println("Exercise 16_PSRAM boot");
+
+  // Boot-time PSRAM diagnostics
+  Serial.printf("Boot PSRAM size: %u bytes\r\n", (unsigned)ESP.getPsramSize());
+  Serial.printf("Boot PSRAM free: %u bytes\r\n", (unsigned)ESP.getFreePsram());
+
+  // Allocate PSRAM buffer
+  g_tmpFileBuffer = (char *)heap_caps_malloc(kTmpFileCapacity, MALLOC_CAP_SPIRAM);
+  if (!g_tmpFileBuffer) {
+    Serial.println("ERROR: Failed to allocate PSRAM buffer!");
+    oledShowLines("Exercise 16_PSRAM", "Node: " NODE_LABEL, "PSRAM alloc FAILED");
+  } else {
+    Serial.printf("PSRAM buffer allocated: %u bytes\r\n", (unsigned)kTmpFileCapacity);
+  }
+
+  Wire.begin(OLED_SDA, OLED_SCL);
+  g_oled.setI2CAddress(OLED_ADDR << 1);
+  g_oled.begin();
+  oledShowLines("Exercise 16_PSRAM", "Node: " NODE_LABEL, "Booting...");
+
+  delay(1000);
+}
+
+void loop()
+{
+  static uint32_t lastMs = 0;
+  const uint32_t now = millis();
+
+  // check serial commands at all times
+  static char rxLine[384];
+  static size_t rxLen = 0;
+
+  while (Serial.available()) {
+    int c = Serial.read();
+    if (c <= 0) continue;
+    if (c == '\r' || c == '\n') {
+      if (rxLen > 0) {
+        rxLine[rxLen] = '\0';
+        processSerialCommand(rxLine);
+        rxLen = 0;
+      }
+    } else if (rxLen + 1 < sizeof(rxLine)) {
+      rxLine[rxLen++] = (char)c;
+    }
+  }
+
+  if (now - lastMs < 1000) {
+    delay(10);
+    return;
+  }
+  lastMs = now;
+
+  if (g_tmpFileBuffer) {
+    appendTimestampLine();
+  }
+  printRamStatus();
+}

exercises/17_Flash/README.md

@@ -0,0 +1,32 @@
+# Exercise 17_Flash
+
+This exercise demonstrates using Flash storage as a persistent directory-like file system on an ESP32-S3 board.
+
+Behavior:
+- Mounts SPIFFS at boot and reports total / used / free flash space.
+- Ensures a flash directory at `/flash_logs` exists.
+- Creates a new log file when the device boots, based on the current timestamp: `YYYYMMDD_HHMM.log`.
+- Writes a timestamped line into the new log file once per second.
+- Supports console commands to inspect the current file, read it, clear it, append or rewrite it, and list stored files.
+- Files persist across reboots and are stored in flash.
+
+Build and upload:
+
+```bash
+cd /usr/local/src/microreticulum/microReticulumTbeam/exercises/17_Flash
+pio run -e amy -t upload
+pio device monitor -b 115200
+```
+
+Commands:
+- `help` - show command menu
+- `stat` - show flash / current file status
+- `list` - list files under `/flash_logs`
+- `read` - read the current flash file contents
+- `clear` - clear the current flash file contents
+- `write <text>` - overwrite the current flash file with text
+- `append <text>` - append text to the current flash file
+
+Notes:
+- If the current timestamp file name already exists, the exercise will append a numeric suffix to keep the file unique.
+- On each reboot a new file is created so persistent flash logs accumulate.

exercises/17_Flash/platformio.ini

@@ -0,0 +1,50 @@
+; 20260403 ChatGPT
+; Exercise 17_Flash
+
+[platformio]
+default_envs = amy
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+monitor_speed = 115200
+extra_scripts = pre:scripts/set_build_epoch.py
+lib_deps =
+  Wire
+  olikraus/U8g2@^2.36.4
+  lewisxhe/XPowersLib@0.3.3
+
+build_flags =
+  -I ../../shared/boards
+  -I ../../external/microReticulum_Firmware
+  -D BOARD_MODEL=BOARD_TBEAM_S_V1
+  -D OLED_SDA=17
+  -D OLED_SCL=18
+  -D OLED_ADDR=0x3C
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+
+[env:amy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"AMY\"
+
+[env:bob]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"BOB\"
+
+[env:cy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"CY\"
+
+[env:dan]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D NODE_LABEL=\"DAN\"

exercises/17_Flash/read_partition_bin.py

@@ -0,0 +1,11 @@
+import struct
+with open('AMY_test_partitions_read.bin', 'rb') as f:
+    data = f.read()
+    seq0 = struct.unpack('<I', data[0:4])[0]
+    seq1 = struct.unpack('<I', data[32:36])[0]
+    print(f"OTA seq0: {seq0:08x}")
+    print(f"OTA seq1: {seq1:08x}")
+    if seq0 > seq1:
+        print("→ app0 is active, new uploads go to app1")
+    else:
+        print("→ app1 is active, new uploads go to app0")

exercises/17_Flash/scripts/set_build_epoch.py

@@ -0,0 +1,12 @@
+import time
+Import("env")
+
+epoch = int(time.time())
+utc_tag = time.strftime("%Y%m%d_%H%M%S_z", time.gmtime(epoch))
+
+env.Append(
+    CPPDEFINES=[
+        ("FW_BUILD_EPOCH", str(epoch)),
+        ("FW_BUILD_UTC", '\"%s\"' % utc_tag),
+    ]
+)

exercises/17_Flash/show_partition_table.py

@@ -0,0 +1,26 @@
+import struct
+
+with open('partitions_backup.bin', 'rb') as f:
+    data = f.read()
+
+print("Name          | Type | SubType | Offset      | Size        | Flags")
+print("-" * 75)
+
+for i in range(0, len(data), 32):
+    entry = data[i:i+32]
+    if len(entry) < 32:
+        break
+    
+    magic = struct.unpack('<H', entry[0:2])[0]
+    
+    if magic == 0x50aa:  # Valid partition magic
+        type_val = entry[2]
+        subtype = entry[3]
+        offset = struct.unpack('<I', entry[4:8])[0]
+        size = struct.unpack('<I', entry[8:12])[0]
+        flags = struct.unpack('<H', entry[12:14])[0]
+        name = entry[16:32].rstrip(b'\x00').decode('ascii', errors='ignore')
+        
+        print(f"{name:<13} | {type_val:02x}   | {subtype:02x}      | 0x{offset:08x}  | 0x{size:08x}  | {flags:04x}")
+    elif magic == 0xebeb:
+        break  # End marker

exercises/17_Flash/src/main.cpp

@@ -0,0 +1,608 @@
+// 20260403 ChatGPT
+// Exercise 17_Flash
+
+#include <Arduino.h>
+#include <Wire.h>
+#include <U8g2lib.h>
+#include <time.h>
+#include <SPIFFS.h>
+
+#include "tbeam_supreme_adapter.h"
+
+#ifndef NODE_LABEL
+#define NODE_LABEL "FLASH"
+#endif
+
+#ifndef RTC_I2C_ADDR
+#define RTC_I2C_ADDR 0x51
+#endif
+
+#ifndef OLED_SDA
+#define OLED_SDA 17
+#endif
+#ifndef OLED_SCL
+#define OLED_SCL 18
+#endif
+#ifndef OLED_ADDR
+#define OLED_ADDR 0x3C
+#endif
+
+static U8G2_SH1106_128X64_NONAME_F_HW_I2C g_oled(U8G2_R0, U8X8_PIN_NONE);
+static const char *kFlashDir = "/flash_logs";
+static char g_currentFilePath[64] = {0};
+static File g_flashFile;
+static unsigned g_flashLineNumber = 0;
+static XPowersLibInterface* g_pmu = nullptr;
+static bool g_hasRtc = false;
+static bool g_rtcLowVoltage = false;
+
+struct RtcDateTime {
+  uint16_t year;
+  uint8_t month;
+  uint8_t day;
+  uint8_t hour;
+  uint8_t minute;
+  uint8_t second;
+  uint8_t weekday;
+};
+
+static void oledShowLines(const char *l1,
+                          const char *l2 = nullptr,
+                          const char *l3 = nullptr,
+                          const char *l4 = nullptr,
+                          const char *l5 = nullptr)
+{
+  g_oled.clearBuffer();
+  g_oled.setFont(u8g2_font_5x8_tf);
+  if (l1) g_oled.drawUTF8(0, 12, l1);
+  if (l2) g_oled.drawUTF8(0, 24, l2);
+  if (l3) g_oled.drawUTF8(0, 36, l3);
+  if (l4) g_oled.drawUTF8(0, 48, l4);
+  if (l5) g_oled.drawUTF8(0, 60, l5);
+  g_oled.sendBuffer();
+}
+
+static size_t getFlashTotalBytes()
+{
+  return SPIFFS.totalBytes();
+}
+
+static size_t getFlashUsedBytes()
+{
+  return SPIFFS.usedBytes();
+}
+
+static size_t getFlashFreeBytes()
+{
+  const size_t total = getFlashTotalBytes();
+  const size_t used = getFlashUsedBytes();
+  return total > used ? total - used : 0;
+}
+
+static uint8_t toBcd(uint8_t v) {
+  return ((v / 10U) << 4U) | (v % 10U);
+}
+
+static uint8_t fromBcd(uint8_t b) {
+  return ((b >> 4U) * 10U) + (b & 0x0FU);
+}
+
+static bool isRtcDateTimeValid(const RtcDateTime& dt) {
+  if (dt.year < 2020 || dt.year > 2099) return false;
+  if (dt.month < 1 || dt.month > 12) return false;
+  if (dt.day < 1 || dt.day > 31) return false;
+  if (dt.hour > 23 || dt.minute > 59 || dt.second > 59) return false;
+  return true;
+}
+
+static bool rtcRead(RtcDateTime& out, bool& lowVoltageFlag) {
+  Wire1.beginTransmission(RTC_I2C_ADDR);
+  Wire1.write(0x02);
+  if (Wire1.endTransmission(false) != 0) {
+    return false;
+  }
+
+  const uint8_t need = 7;
+  uint8_t got = Wire1.requestFrom((int)RTC_I2C_ADDR, (int)need);
+  if (got != need) {
+    return false;
+  }
+
+  uint8_t sec = Wire1.read();
+  uint8_t min = Wire1.read();
+  uint8_t hour = Wire1.read();
+  uint8_t day = Wire1.read();
+  uint8_t weekday = Wire1.read();
+  uint8_t month = Wire1.read();
+  uint8_t year = Wire1.read();
+
+  lowVoltageFlag = (sec & 0x80U) != 0;
+  out.second = fromBcd(sec & 0x7FU);
+  out.minute = fromBcd(min & 0x7FU);
+  out.hour = fromBcd(hour & 0x3FU);
+  out.day = fromBcd(day & 0x3FU);
+  out.weekday = fromBcd(weekday & 0x07U);
+  out.month = fromBcd(month & 0x1FU);
+  uint8_t yy = fromBcd(year);
+  bool century = (month & 0x80U) != 0;
+  out.year = century ? (1900U + yy) : (2000U + yy);
+
+  return true;
+}
+
+static bool initRtc() {
+  if (!tbeam_supreme::initPmuForPeripherals(g_pmu, &Serial)) {
+    Serial.println("RTC init: PMU/i2c init failed");
+    return false;
+  }
+  RtcDateTime now{};
+  if (!rtcRead(now, g_rtcLowVoltage) || !isRtcDateTimeValid(now)) {
+    Serial.println("RTC init: no valid time available");
+    return false;
+  }
+  g_hasRtc = true;
+  Serial.printf("RTC init: %04u-%02u-%02u %02u:%02u:%02u%s\r\n",
+                (unsigned)now.year, (unsigned)now.month, (unsigned)now.day,
+                (unsigned)now.hour, (unsigned)now.minute, (unsigned)now.second,
+                g_rtcLowVoltage ? " [LOW_BATT]" : "");
+  return true;
+}
+
+static bool getRtcTimestamp(char *out, size_t outSize) {
+  if (!g_hasRtc) {
+    return false;
+  }
+  RtcDateTime now{};
+  bool low = false;
+  if (!rtcRead(now, low) || !isRtcDateTimeValid(now)) {
+    return false;
+  }
+  g_rtcLowVoltage = low;
+  snprintf(out, outSize, "%04u-%02u-%02u %02u:%02u:%02u",
+           now.year,
+           now.month,
+           now.day,
+           now.hour,
+           now.minute,
+           now.second);
+  return true;
+}
+
+static void getTimestamp(char *out, size_t outSize)
+{
+  if (getRtcTimestamp(out, outSize)) {
+    return;
+  }
+
+  const time_t now = time(nullptr);
+  if (now > 1700000000) {
+    struct tm tmNow;
+    localtime_r(&now, &tmNow);
+    snprintf(out, outSize, "%04d-%02d-%02d %02d:%02d:%02d",
+             tmNow.tm_year + 1900,
+             tmNow.tm_mon + 1,
+             tmNow.tm_mday,
+             tmNow.tm_hour,
+             tmNow.tm_min,
+             tmNow.tm_sec);
+    return;
+  }
+
+  const uint32_t sec = millis() / 1000;
+  const uint32_t hh = sec / 3600;
+  const uint32_t mm = (sec % 3600) / 60;
+  const uint32_t ss = sec % 60;
+  snprintf(out, outSize, "uptime %02u:%02u:%02u", (unsigned)hh, (unsigned)mm, (unsigned)ss);
+}
+
+static void getFilenameTimestamp(char *out, size_t outSize)
+{
+  if (g_hasRtc) {
+    RtcDateTime now{};
+    bool low = false;
+    if (rtcRead(now, low) && isRtcDateTimeValid(now)) {
+      snprintf(out, outSize, "%04u%02u%02u_%02u%02u",
+               now.year,
+               now.month,
+               now.day,
+               now.hour,
+               now.minute);
+      return;
+    }
+  }
+
+  const time_t now = time(nullptr);
+  if (now > 1700000000) {
+    struct tm tmNow;
+    localtime_r(&now, &tmNow);
+    snprintf(out, outSize, "%04d%02d%02d_%02d%02d",
+             tmNow.tm_year + 1900,
+             tmNow.tm_mon + 1,
+             tmNow.tm_mday,
+             tmNow.tm_hour,
+             tmNow.tm_min);
+    return;
+  }
+
+  const uint32_t sec = millis() / 1000;
+  const uint32_t hh = sec / 3600;
+  const uint32_t mm = (sec % 3600) / 60;
+  const uint32_t ss = sec % 60;
+  snprintf(out, outSize, "uptime_%02u%02u%02u", (unsigned)hh, (unsigned)mm, (unsigned)ss);
+}
+
+static String getNewFlashFilePath()
+{
+  char baseName[64];
+  getFilenameTimestamp(baseName, sizeof(baseName));
+
+  char candidate[96];
+  snprintf(candidate, sizeof(candidate), "%s/%s.log", kFlashDir, baseName);
+  if (!SPIFFS.exists(candidate)) {
+    return String(candidate);
+  }
+
+  int suffix = 1;
+  do {
+    snprintf(candidate, sizeof(candidate), "%s/%s-%d.log", kFlashDir, baseName, suffix);
+    suffix += 1;
+  } while (SPIFFS.exists(candidate));
+
+  return String(candidate);
+}
+
+static bool ensureFlashDirectory()
+{
+  if (SPIFFS.exists(kFlashDir)) {
+    return true;
+  }
+  if (!SPIFFS.mkdir(kFlashDir)) {
+    Serial.printf("Warning: failed to create %s\r\n", kFlashDir);
+    return false;
+  }
+  return true;
+}
+
+static bool openCurrentFlashFile(bool truncate = false)
+{
+  if (g_flashFile) {
+    g_flashFile.close();
+  }
+
+  if (truncate) {
+    g_flashFile = SPIFFS.open(g_currentFilePath, FILE_WRITE);
+  } else {
+    g_flashFile = SPIFFS.open(g_currentFilePath, FILE_APPEND);
+  }
+
+  if (!g_flashFile) {
+    Serial.printf("ERROR: cannot open %s\r\n", g_currentFilePath);
+    return false;
+  }
+  return true;
+}
+
+static bool createFlashLogFile()
+{
+  if (!ensureFlashDirectory()) {
+    return false;
+  }
+
+  String path = getNewFlashFilePath();
+  path.toCharArray(g_currentFilePath, sizeof(g_currentFilePath));
+
+  g_flashFile = SPIFFS.open(g_currentFilePath, FILE_WRITE);
+  if (!g_flashFile) {
+    Serial.printf("ERROR: could not create %s\r\n", g_currentFilePath);
+    return false;
+  }
+
+  const char *header = "FLASH log file created\r\n";
+  g_flashFile.print(header);
+  g_flashFile.flush();
+  g_flashLineNumber = 0;
+  return true;
+}
+
+static void appendFlashTimestampLine()
+{
+  if (!g_flashFile) {
+    return;
+  }
+
+  char timestamp[32];
+  getTimestamp(timestamp, sizeof(timestamp));
+
+  char line[96];
+  const int written = snprintf(line, sizeof(line), "%u, %s\r\n", g_flashLineNumber + 1, timestamp);
+  if (written <= 0) {
+    return;
+  }
+
+  const size_t lineLen = (size_t)written;
+  if (g_flashFile.write(reinterpret_cast<const uint8_t *>(line), lineLen) != lineLen) {
+    Serial.println("Warning: flash write failed");
+    return;
+  }
+  g_flashFile.flush();
+  g_flashLineNumber += 1;
+}
+
+static void printFlashStatus()
+{
+  const size_t total = getFlashTotalBytes();
+  const size_t used = getFlashUsedBytes();
+  const size_t freeBytes = getFlashFreeBytes();
+
+  Serial.printf("FLASH total=%u used=%u free=%u\r\n",
+                (unsigned)total, (unsigned)used, (unsigned)freeBytes);
+
+  char line1[32];
+  char line2[32];
+  char line3[32];
+  char line4[32];
+  char line5[32];
+
+  snprintf(line1, sizeof(line1), "Exercise 17 Flash");
+  snprintf(line2, sizeof(line2), "Node: %s", NODE_LABEL);
+  snprintf(line3, sizeof(line3), "Free: %u KB", (unsigned)(freeBytes / 1024U));
+  snprintf(line4, sizeof(line4), "Used: %u KB", (unsigned)(used / 1024U));
+  snprintf(line5, sizeof(line5), "Lines: %u", (unsigned)g_flashLineNumber);
+
+  oledShowLines(line1, line2, line3, line4, line5);
+}
+
+static void showHelp()
+{
+  Serial.println("Flash command list:");
+  Serial.println("  help           - show this menu");
+  Serial.println("  stat           - show flash/file state");
+  Serial.println("  rtc            - show RTC time status");
+  Serial.println("  list           - list files in /flash_logs");
+  Serial.println("  read           - read current flash file");
+  Serial.println("  clear          - clear current flash file");
+  Serial.println("  write <text>   - overwrite current flash file");
+  Serial.println("  append <text>  - append text to current flash file");
+}
+
+static void printFlashFileStat()
+{
+  Serial.printf("Current file: %s\r\n", g_currentFilePath);
+  if (!SPIFFS.exists(g_currentFilePath)) {
+    Serial.println("Current file missing");
+    return;
+  }
+
+  File file = SPIFFS.open(g_currentFilePath, FILE_READ);
+  if (!file) {
+    Serial.println("Unable to open current file for stats");
+    return;
+  }
+
+  Serial.printf("Size: %u bytes\r\n", (unsigned)file.size());
+  Serial.printf("Lines written: %u\r\n", (unsigned)g_flashLineNumber);
+  file.close();
+}
+
+static void printFlashFileContents()
+{
+  if (!SPIFFS.exists(g_currentFilePath)) {
+    Serial.println("Current flash file does not exist");
+    return;
+  }
+
+  File file = SPIFFS.open(g_currentFilePath, FILE_READ);
+  if (!file) {
+    Serial.println("Unable to open current flash file");
+    return;
+  }
+
+  if (file.size() == 0) {
+    Serial.println("Current flash file is empty");
+    file.close();
+    return;
+  }
+
+  Serial.print("Flash file contents: ");
+  while (file.available()) {
+    Serial.write(file.read());
+  }
+  if (file.size() > 0) {
+    Serial.println();
+  }
+  file.close();
+}
+
+static void clearFlashFileContents()
+{
+  if (!SPIFFS.exists(g_currentFilePath)) {
+    Serial.println("No current file to clear");
+    return;
+  }
+
+  if (!openCurrentFlashFile(true)) {
+    return;
+  }
+  g_flashFile.close();
+  g_flashLineNumber = 0;
+  openCurrentFlashFile(false);
+  Serial.println("Current flash file cleared");
+}
+
+static void setFlashFileContent(const char *text)
+{
+  if (!text) {
+    clearFlashFileContents();
+    return;
+  }
+
+  File file = SPIFFS.open(g_currentFilePath, FILE_WRITE);
+  if (!file) {
+    Serial.println("Unable to overwrite current flash file");
+    return;
+  }
+
+  file.print(text);
+  file.close();
+  openCurrentFlashFile(false);
+  g_flashLineNumber = 0;
+}
+
+static void appendFlashFileContent(const char *text)
+{
+  if (!text || text[0] == '\0') {
+    return;
+  }
+
+  if (!openCurrentFlashFile(false)) {
+    return;
+  }
+
+  g_flashFile.print(text);
+  g_flashFile.flush();
+}
+
+static void listFlashFiles()
+{
+  File dir = SPIFFS.open(kFlashDir);
+  if (!dir || !dir.isDirectory()) {
+    Serial.printf("Unable to list files in %s\r\n", kFlashDir);
+    return;
+  }
+
+  Serial.printf("Files in %s:\r\n", kFlashDir);
+  File file = dir.openNextFile();
+  while (file) {
+    Serial.printf("  %s (%u bytes)\r\n", file.name(), (unsigned)file.size());
+    file = dir.openNextFile();
+  }
+  dir.close();
+}
+
+static void processSerialCommand(const char *line)
+{
+  if (!line || line[0] == '\0') return;
+
+  char tmp[384];
+  strncpy(tmp, line, sizeof(tmp) - 1);
+  tmp[sizeof(tmp) - 1] = '\0';
+
+  char *cmd = strtok(tmp, " \t\r\n");
+  if (!cmd) return;
+
+  if (strcasecmp(cmd, "help") == 0) {
+    showHelp();
+    return;
+  }
+
+  if (strcasecmp(cmd, "stat") == 0) {
+    printFlashFileStat();
+    return;
+  }
+
+  if (strcasecmp(cmd, "rtc") == 0) {
+    if (g_hasRtc) {
+      char ts[32];
+      if (getRtcTimestamp(ts, sizeof(ts))) {
+        Serial.printf("RTC now: %s\r\n", ts);
+        if (g_rtcLowVoltage) {
+          Serial.println("RTC low-voltage flag is set");
+        }
+      } else {
+        Serial.println("RTC present but time read failed");
+      }
+    } else {
+      Serial.println("RTC unavailable");
+    }
+    return;
+  }
+
+  if (strcasecmp(cmd, "list") == 0) {
+    listFlashFiles();
+    return;
+  }
+
+  if (strcasecmp(cmd, "read") == 0) {
+    printFlashFileContents();
+    return;
+  }
+
+  if (strcasecmp(cmd, "clear") == 0) {
+    clearFlashFileContents();
+    return;
+  }
+
+  if (strcasecmp(cmd, "write") == 0 || strcasecmp(cmd, "append") == 0) {
+    const char *payload = line + strlen(cmd);
+    while (*payload == ' ' || *payload == '\t') payload++;
+    if (strcasecmp(cmd, "write") == 0)
+      setFlashFileContent(payload);
+    else
+      appendFlashFileContent(payload);
+
+    Serial.printf("%s: %s\r\n", cmd, payload);
+    return;
+  }
+
+  Serial.println("Unknown command (help for list)");
+}
+
+void setup()
+{
+  Serial.begin(115200);
+  delay(800);
+  Serial.println("Exercise 17_Flash boot");
+
+  initRtc();
+
+  if (!SPIFFS.begin(true)) {
+    Serial.println("ERROR: SPIFFS mount failed");
+    oledShowLines("Exercise 17_Flash", "Node: " NODE_LABEL, "SPIFFS mount FAILED");
+  } else {
+    Serial.println("SPIFFS mounted successfully");
+    if (createFlashLogFile()) {
+      Serial.printf("Current flash file: %s\r\n", g_currentFilePath);
+    }
+  }
+
+  Wire.begin(OLED_SDA, OLED_SCL);
+  g_oled.setI2CAddress(OLED_ADDR << 1);
+  g_oled.begin();
+  oledShowLines("Exercise 17_Flash", "Node: " NODE_LABEL, "Booting...");
+
+  delay(1000);
+}
+
+void loop()
+{
+  static uint32_t lastMs = 0;
+  const uint32_t now = millis();
+
+  static char rxLine[384];
+  static size_t rxLen = 0;
+
+  while (Serial.available()) {
+    int c = Serial.read();
+    if (c <= 0) continue;
+    if (c == '\r' || c == '\n') {
+      if (rxLen > 0) {
+        rxLine[rxLen] = '\0';
+        processSerialCommand(rxLine);
+        rxLen = 0;
+      }
+    } else if (rxLen + 1 < sizeof(rxLine)) {
+      rxLine[rxLen++] = (char)c;
+    }
+  }
+
+  if (now - lastMs < 1000) {
+    delay(10);
+    return;
+  }
+  lastMs = now;
+
+  if (g_flashFile) {
+    appendFlashTimestampLine();
+  }
+  printFlashStatus();
+}

exercises/18_GPS_Field_QA/README.md

@@ -0,0 +1,38 @@
+## Exercise 18: GPS Field QA
+
+Survey/reconnaissance firmware for LilyGO T-Beam SUPREME.
+
+This exercise measures GNSS visibility and solution quality, disciplines the RTC from GNSS before creating any capture log, writes CSV captures to SD card, and exposes the SD tree over the field AP for download and erase operations.
+
+Current storage choice:
+
+- `SD`
+
+Current environments:
+
+- `bob_l76k`
+- `guy_ublox`
+
+Primary serial commands:
+
+- `status`
+- `summary`
+- `ls`
+- `cat <path>`
+- `erase <path>`
+- `stop`
+- `start`
+- `flush`
+- `discipline`
+- `erase_logs`
+
+Notes:
+
+- Default environment is `cy`.
+- No log file is created until GNSS UTC plus PPS has disciplined the RTC.
+- The capture file naming format is `YYYYMMDD_HHMMSS_<BOARD>.csv`.
+- Samples are aggregated once per second.
+- Records are double-buffered in RAM and flushed to SD every 10 seconds.
+- Satellite snapshot records are written as additional CSV lines when GSV data is available.
+- The web UI exposes SD download links and `/cmd?...` actions such as `erase=/logs/20260406_093912_CY.csv`.
+- The implementation uses common NMEA parsing so it can normalize L76K and MAX-M10S output without adding a new GNSS dependency.

exercises/18_GPS_Field_QA/lib/field_qa/ClockDiscipline.cpp

@@ -0,0 +1,241 @@
+#include "ClockDiscipline.h"
+
+#include "Config.h"
+
+namespace field_qa {
+
+ClockDiscipline::ClockDiscipline(TwoWire& wire) : m_wire(wire) {}
+
+uint8_t ClockDiscipline::toBcd(uint8_t value) {
+  return (uint8_t)(((value / 10U) << 4U) | (value % 10U));
+}
+
+uint8_t ClockDiscipline::fromBcd(uint8_t value) {
+  return (uint8_t)(((value >> 4U) * 10U) + (value & 0x0FU));
+}
+
+bool ClockDiscipline::isLeapYear(uint16_t year) {
+  return ((year % 4U) == 0U && (year % 100U) != 0U) || ((year % 400U) == 0U);
+}
+
+uint8_t ClockDiscipline::daysInMonth(uint16_t year, uint8_t month) {
+  static const uint8_t kDays[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
+  if (month == 2U) {
+    return (uint8_t)(isLeapYear(year) ? 29U : 28U);
+  }
+  if (month >= 1U && month <= 12U) {
+    return kDays[month - 1U];
+  }
+  return 0;
+}
+
+bool ClockDiscipline::isValidDateTime(const ClockDateTime& dt) {
+  if (dt.year < 2000U || dt.year > 2099U) {
+    return false;
+  }
+  if (dt.month < 1U || dt.month > 12U) {
+    return false;
+  }
+  if (dt.day < 1U || dt.day > daysInMonth(dt.year, dt.month)) {
+    return false;
+  }
+  if (dt.hour > 23U || dt.minute > 59U || dt.second > 59U) {
+    return false;
+  }
+  return true;
+}
+
+int64_t ClockDiscipline::daysFromCivil(int year, unsigned month, unsigned day) {
+  year -= (month <= 2U);
+  const int era = (year >= 0 ? year : year - 399) / 400;
+  const unsigned yoe = (unsigned)(year - era * 400);
+  const unsigned doy = (153U * (month + (month > 2U ? (unsigned)-3 : 9U)) + 2U) / 5U + day - 1U;
+  const unsigned doe = yoe * 365U + yoe / 4U - yoe / 100U + doy;
+  return era * 146097 + (int)doe - 719468;
+}
+
+int64_t ClockDiscipline::toEpochSeconds(const ClockDateTime& dt) {
+  const int64_t days = daysFromCivil((int)dt.year, dt.month, dt.day);
+  return days * 86400LL + (int64_t)dt.hour * 3600LL + (int64_t)dt.minute * 60LL + (int64_t)dt.second;
+}
+
+bool ClockDiscipline::fromEpochSeconds(int64_t seconds, ClockDateTime& out) {
+  if (seconds < 0) {
+    return false;
+  }
+
+  int64_t days = seconds / 86400LL;
+  int64_t remainder = seconds % 86400LL;
+  if (remainder < 0) {
+    remainder += 86400LL;
+    days -= 1;
+  }
+
+  out.hour = (uint8_t)(remainder / 3600LL);
+  remainder %= 3600LL;
+  out.minute = (uint8_t)(remainder / 60LL);
+  out.second = (uint8_t)(remainder % 60LL);
+
+  days += 719468;
+  const int era = (days >= 0 ? days : days - 146096) / 146097;
+  const unsigned doe = (unsigned)(days - era * 146097);
+  const unsigned yoe = (doe - doe / 1460U + doe / 36524U - doe / 146096U) / 365U;
+  int year = (int)yoe + era * 400;
+  const unsigned doy = doe - (365U * yoe + yoe / 4U - yoe / 100U);
+  const unsigned mp = (5U * doy + 2U) / 153U;
+  const unsigned day = doy - (153U * mp + 2U) / 5U + 1U;
+  const unsigned month = mp + (mp < 10U ? 3U : (unsigned)-9);
+  year += (month <= 2U);
+
+  out.year = (uint16_t)year;
+  out.month = (uint8_t)month;
+  out.day = (uint8_t)day;
+  return isValidDateTime(out);
+}
+
+bool ClockDiscipline::readRtc(ClockDateTime& out, bool& lowVoltageFlag) const {
+  m_wire.beginTransmission(RTC_I2C_ADDR);
+  m_wire.write(0x02);
+  if (m_wire.endTransmission(false) != 0) {
+    return false;
+  }
+
+  const uint8_t need = 7;
+  const uint8_t got = m_wire.requestFrom((int)RTC_I2C_ADDR, (int)need);
+  if (got != need) {
+    return false;
+  }
+
+  const uint8_t sec = m_wire.read();
+  const uint8_t min = m_wire.read();
+  const uint8_t hour = m_wire.read();
+  const uint8_t day = m_wire.read();
+  (void)m_wire.read();
+  const uint8_t month = m_wire.read();
+  const uint8_t year = m_wire.read();
+
+  lowVoltageFlag = (sec & 0x80U) != 0;
+  out.second = fromBcd(sec & 0x7FU);
+  out.minute = fromBcd(min & 0x7FU);
+  out.hour = fromBcd(hour & 0x3FU);
+  out.day = fromBcd(day & 0x3FU);
+  out.month = fromBcd(month & 0x1FU);
+  const uint8_t yy = fromBcd(year);
+  out.year = (month & 0x80U) ? (1900U + yy) : (2000U + yy);
+  return true;
+}
+
+bool ClockDiscipline::readValidRtc(ClockDateTime& out, int64_t* epochOut) const {
+  bool lowVoltage = false;
+  if (!readRtc(out, lowVoltage) || lowVoltage || !isValidDateTime(out)) {
+    return false;
+  }
+  if (epochOut != nullptr) {
+    *epochOut = toEpochSeconds(out);
+  }
+  return true;
+}
+
+bool ClockDiscipline::writeRtc(const ClockDateTime& dt) const {
+  if (!isValidDateTime(dt)) {
+    return false;
+  }
+
+  m_wire.beginTransmission(RTC_I2C_ADDR);
+  m_wire.write(0x02);
+  m_wire.write(toBcd(dt.second & 0x7FU));
+  m_wire.write(toBcd(dt.minute));
+  m_wire.write(toBcd(dt.hour));
+  m_wire.write(toBcd(dt.day));
+  m_wire.write(0x00);
+
+  uint8_t monthReg = toBcd(dt.month);
+  if (dt.year < 2000U) {
+    monthReg |= 0x80U;
+  }
+  m_wire.write(monthReg);
+  m_wire.write(toBcd((uint8_t)(dt.year % 100U)));
+  return m_wire.endTransmission() == 0;
+}
+
+void ClockDiscipline::formatIsoUtc(const ClockDateTime& dt, char* out, size_t outSize) {
+  snprintf(out,
+           outSize,
+           "%04u-%02u-%02uT%02u:%02u:%02uZ",
+           (unsigned)dt.year,
+           (unsigned)dt.month,
+           (unsigned)dt.day,
+           (unsigned)dt.hour,
+           (unsigned)dt.minute,
+           (unsigned)dt.second);
+}
+
+void ClockDiscipline::formatCompactUtc(const ClockDateTime& dt, char* out, size_t outSize) {
+  snprintf(out,
+           outSize,
+           "%04u%02u%02u_%02u%02u%02u",
+           (unsigned)dt.year,
+           (unsigned)dt.month,
+           (unsigned)dt.day,
+           (unsigned)dt.hour,
+           (unsigned)dt.minute,
+           (unsigned)dt.second);
+}
+
+void ClockDiscipline::makeRunId(const ClockDateTime& dt, const char* boardId, char* out, size_t outSize) {
+  snprintf(out,
+           outSize,
+           "%04u%02u%02u_%02u%02u%02u_%s",
+           (unsigned)dt.year,
+           (unsigned)dt.month,
+           (unsigned)dt.day,
+           (unsigned)dt.hour,
+           (unsigned)dt.minute,
+           (unsigned)dt.second,
+           boardId ? boardId : "NODE");
+}
+
+bool ClockDiscipline::fromGnssSample(const GnssSample& sample, ClockDateTime& out) {
+  if (!sample.validTime) {
+    return false;
+  }
+  out.year = sample.year;
+  out.month = sample.month;
+  out.day = sample.day;
+  out.hour = sample.hour;
+  out.minute = sample.minute;
+  out.second = sample.second;
+  return isValidDateTime(out);
+}
+
+bool ClockDiscipline::disciplineFromGnss(const GnssSample& sample,
+                                         WaitForPpsCallback waitForPps,
+                                         void* context,
+                                         ClockDateTime& disciplinedUtc,
+                                         bool& hadPriorRtc,
+                                         int64_t& driftSeconds) const {
+  ClockDateTime gpsUtc{};
+  if (!fromGnssSample(sample, gpsUtc) || waitForPps == nullptr) {
+    return false;
+  }
+
+  ClockDateTime priorRtc{};
+  hadPriorRtc = readValidRtc(priorRtc, nullptr);
+
+  if (!waitForPps(context, kClockPpsWaitTimeoutMs)) {
+    return false;
+  }
+
+  const int64_t snappedEpoch = toEpochSeconds(gpsUtc);
+  if (!fromEpochSeconds(snappedEpoch + 1, disciplinedUtc)) {
+    return false;
+  }
+  if (!writeRtc(disciplinedUtc)) {
+    return false;
+  }
+
+  driftSeconds = hadPriorRtc ? (toEpochSeconds(priorRtc) - toEpochSeconds(disciplinedUtc)) : 0;
+  return true;
+}
+
+}  // namespace field_qa

exercises/18_GPS_Field_QA/lib/field_qa/ClockDiscipline.h

@@ -0,0 +1,53 @@
+#pragma once
+
+#include <Arduino.h>
+#include <Wire.h>
+#include "GnssTypes.h"
+
+namespace field_qa {
+
+struct ClockDateTime {
+  uint16_t year = 0;
+  uint8_t month = 0;
+  uint8_t day = 0;
+  uint8_t hour = 0;
+  uint8_t minute = 0;
+  uint8_t second = 0;
+};
+
+using WaitForPpsCallback = bool (*)(void* context, uint32_t timeoutMs);
+
+class ClockDiscipline {
+ public:
+  explicit ClockDiscipline(TwoWire& wire = Wire1);
+
+  bool readRtc(ClockDateTime& out, bool& lowVoltageFlag) const;
+  bool readValidRtc(ClockDateTime& out, int64_t* epochOut = nullptr) const;
+  bool writeRtc(const ClockDateTime& dt) const;
+
+  bool disciplineFromGnss(const GnssSample& sample,
+                          WaitForPpsCallback waitForPps,
+                          void* context,
+                          ClockDateTime& disciplinedUtc,
+                          bool& hadPriorRtc,
+                          int64_t& driftSeconds) const;
+
+  static bool isValidDateTime(const ClockDateTime& dt);
+  static int64_t toEpochSeconds(const ClockDateTime& dt);
+  static bool fromEpochSeconds(int64_t seconds, ClockDateTime& out);
+  static void formatIsoUtc(const ClockDateTime& dt, char* out, size_t outSize);
+  static void formatCompactUtc(const ClockDateTime& dt, char* out, size_t outSize);
+  static void makeRunId(const ClockDateTime& dt, const char* boardId, char* out, size_t outSize);
+  static bool fromGnssSample(const GnssSample& sample, ClockDateTime& out);
+
+ private:
+  static uint8_t toBcd(uint8_t value);
+  static uint8_t fromBcd(uint8_t value);
+  static bool isLeapYear(uint16_t year);
+  static uint8_t daysInMonth(uint16_t year, uint8_t month);
+  static int64_t daysFromCivil(int year, unsigned month, unsigned day);
+
+  TwoWire& m_wire;
+};
+
+}  // namespace field_qa

exercises/18_GPS_Field_QA/lib/field_qa/Config.h

@@ -0,0 +1,84 @@
+#pragma once
+
+#include <Arduino.h>
+
+#ifndef BOARD_ID
+#define BOARD_ID "BOB"
+#endif
+
+#ifndef GNSS_CHIP_NAME
+#define GNSS_CHIP_NAME "L76K"
+#endif
+
+#ifndef OLED_SDA
+#define OLED_SDA 17
+#endif
+
+#ifndef OLED_SCL
+#define OLED_SCL 18
+#endif
+
+#ifndef OLED_ADDR
+#define OLED_ADDR 0x3C
+#endif
+
+#ifndef RTC_I2C_ADDR
+#define RTC_I2C_ADDR 0x51
+#endif
+
+#ifndef GPS_BAUD
+#define GPS_BAUD 9600
+#endif
+
+#ifndef GPS_RX_PIN
+#define GPS_RX_PIN 9
+#endif
+
+#ifndef GPS_TX_PIN
+#define GPS_TX_PIN 8
+#endif
+
+#ifndef BUTTON_PIN
+#define BUTTON_PIN 0
+#endif
+
+#ifndef FW_BUILD_UTC
+#define FW_BUILD_UTC unknown
+#endif
+
+#define FIELD_QA_STR_INNER(x) #x
+#define FIELD_QA_STR(x) FIELD_QA_STR_INNER(x)
+
+namespace field_qa {
+
+static constexpr const char* kExerciseName = "18_GPS_Field_QA";
+static constexpr const char* kFirmwareVersion = FIELD_QA_STR(FW_BUILD_UTC);
+static constexpr const char* kBoardId = BOARD_ID;
+static constexpr const char* kGnssChip = GNSS_CHIP_NAME;
+static constexpr const char* kStorageName = "SD";
+static constexpr const char* kLogDir = "/logs";
+static constexpr const char* kLogApPrefix = "GPSQA-";
+static constexpr const char* kLogApPassword = "";
+static constexpr uint8_t kLogApIpOctet = 23;
+static constexpr uint32_t kSerialDelayMs = 4000;
+static constexpr uint32_t kSamplePeriodMs = 1000;
+static constexpr uint32_t kLogFlushPeriodMs = 10000;
+static constexpr uint32_t kDisplayPeriodMs = 1000;
+static constexpr uint32_t kStatusPeriodMs = 1000;
+static constexpr uint32_t kProbeWindowL76kMs = 20000;
+static constexpr uint32_t kProbeWindowUbloxMs = 45000;
+static constexpr uint32_t kFixFreshMs = 5000;
+static constexpr uint8_t kPoorMinSatsUsed = 4;
+static constexpr uint8_t kGoodMinSatsUsed = 10;
+static constexpr uint8_t kExcellentMinSatsUsed = 16;
+static constexpr float kMarginalHdop = 3.0f;
+static constexpr float kExcellentHdop = 1.5f;
+static constexpr size_t kBufferedSamples = 10;
+static constexpr size_t kMaxSatellites = 64;
+static constexpr size_t kStorageBufferBytes = 4096;
+static constexpr uint32_t kClockDisciplineRetryMs = 5000;
+static constexpr uint32_t kClockPpsWaitTimeoutMs = 1500;
+static constexpr uint32_t kClockFreshSampleMs = 2000;
+static constexpr uint32_t kMaxLogFilesBeforePause = 1000;
+
+}  // namespace field_qa

exercises/18_GPS_Field_QA/lib/field_qa/DisplayManager.cpp

@@ -0,0 +1,72 @@
+#include "DisplayManager.h"
+
+#include <Wire.h>
+#include "Config.h"
+
+namespace field_qa {
+
+namespace {
+
+static void formatElapsed(uint32_t ms, char* out, size_t outSize) {
+  const uint32_t sec = ms / 1000U;
+  const uint32_t hh = sec / 3600U;
+  const uint32_t mm = (sec % 3600U) / 60U;
+  const uint32_t ss = sec % 60U;
+  snprintf(out, outSize, "%02lu:%02lu:%02lu", (unsigned long)hh, (unsigned long)mm, (unsigned long)ss);
+}
+
+}  // namespace
+
+void DisplayManager::begin() {
+  Wire.begin(OLED_SDA, OLED_SCL);
+  m_oled.setI2CAddress(OLED_ADDR << 1);
+  m_oled.begin();
+}
+
+void DisplayManager::drawLines(const char* l1,
+                               const char* l2,
+                               const char* l3,
+                               const char* l4,
+                               const char* l5,
+                               const char* l6) {
+  m_oled.clearBuffer();
+  m_oled.setFont(u8g2_font_5x8_tf);
+  if (l1) m_oled.drawUTF8(0, 10, l1);
+  if (l2) m_oled.drawUTF8(0, 20, l2);
+  if (l3) m_oled.drawUTF8(0, 30, l3);
+  if (l4) m_oled.drawUTF8(0, 40, l4);
+  if (l5) m_oled.drawUTF8(0, 50, l5);
+  if (l6) m_oled.drawUTF8(0, 60, l6);
+  m_oled.sendBuffer();
+}
+
+void DisplayManager::showBoot(const char* line2, const char* line3) {
+  drawLines(kExerciseName, kFirmwareVersion, line2, line3);
+}
+
+void DisplayManager::showError(const char* line1, const char* line2) {
+  drawLines(kExerciseName, "ERROR", line1, line2);
+}
+
+void DisplayManager::showSample(const GnssSample& sample, const RunStats& stats, bool recording) {
+  char l1[24];
+  char l2[20];
+  char l3[20];
+  char l4[20];
+  char l5[20];
+  char l6[20];
+
+  snprintf(l1, sizeof(l1), "%s", recording ? "*RECORDING" : "Halted");
+  snprintf(l2, sizeof(l2), "FIX: %s", fixTypeToString(sample.fixType));
+  snprintf(l3, sizeof(l3), "USED: %d/%d", sample.satsUsed < 0 ? 0 : sample.satsUsed, sample.satsInView < 0 ? 0 : sample.satsInView);
+  if (sample.validHdop) {
+    snprintf(l4, sizeof(l4), "HDOP: %.1f", sample.hdop);
+  } else {
+    snprintf(l4, sizeof(l4), "HDOP: --");
+  }
+  snprintf(l5, sizeof(l5), "Q: %s", qualityClassForSample(sample));
+  formatElapsed(stats.elapsedMs(millis()), l6, sizeof(l6));
+  drawLines(l1, l2, l3, l4, l5, l6);
+}
+
+}  // namespace field_qa

exercises/18_GPS_Field_QA/lib/field_qa/DisplayManager.h

@@ -0,0 +1,28 @@
+#pragma once
+
+#include <Arduino.h>
+#include <U8g2lib.h>
+#include "GnssTypes.h"
+#include "RunStats.h"
+
+namespace field_qa {
+
+class DisplayManager {
+ public:
+  void begin();
+  void showBoot(const char* line2, const char* line3 = nullptr);
+  void showError(const char* line1, const char* line2 = nullptr);
+  void showSample(const GnssSample& sample, const RunStats& stats, bool recording);
+
+ private:
+  void drawLines(const char* l1,
+                 const char* l2 = nullptr,
+                 const char* l3 = nullptr,
+                 const char* l4 = nullptr,
+                 const char* l5 = nullptr,
+                 const char* l6 = nullptr);
+
+  U8G2_SH1106_128X64_NONAME_F_HW_I2C m_oled{U8G2_R0, U8X8_PIN_NONE};
+};
+
+}  // namespace field_qa

exercises/18_GPS_Field_QA/lib/field_qa/GnssManager.cpp

@@ -0,0 +1,488 @@
+#include "GnssManager.h"
+
+#include <ctype.h>
+#include <math.h>
+#include <string.h>
+#include "Config.h"
+
+namespace field_qa {
+
+namespace {
+
+enum class GpsModuleKind : uint8_t {
+  Unknown = 0,
+  L76K,
+  Ublox
+};
+
+#if defined(GPS_UBLOX)
+static constexpr GpsModuleKind kExpectedGpsModule = GpsModuleKind::Ublox;
+#elif defined(GPS_L76K)
+static constexpr GpsModuleKind kExpectedGpsModule = GpsModuleKind::L76K;
+#else
+static constexpr GpsModuleKind kExpectedGpsModule = GpsModuleKind::Unknown;
+#endif
+
+static GpsModuleKind talkerToConstellation(const char* talker) {
+  if (!talker) return GpsModuleKind::Unknown;
+  if (strcmp(talker, "GP") == 0) return GpsModuleKind::L76K;
+  if (strcmp(talker, "GA") == 0) return GpsModuleKind::Ublox;
+  return GpsModuleKind::Unknown;
+}
+
+static FixType fixTypeFromQuality(int quality, int dimension) {
+  switch (quality) {
+    case 2:
+      return FixType::Dgps;
+    case 4:
+      return FixType::RtkFixed;
+    case 5:
+      return FixType::RtkFloat;
+    default:
+      if (dimension >= 3) return FixType::Fix3D;
+      if (dimension == 2) return FixType::Fix2D;
+      return FixType::NoFix;
+  }
+}
+
+static void copyTalker(const char* header, char* out) {
+  if (!header || strlen(header) < 3) {
+    out[0] = '?';
+    out[1] = '?';
+    out[2] = '\0';
+    return;
+  }
+  out[0] = header[1];
+  out[1] = header[2];
+  out[2] = '\0';
+}
+
+}  // namespace
+
+void GnssManager::begin() {
+  m_bootMs = millis();
+  strlcpy(m_detectedChip, kGnssChip, sizeof(m_detectedChip));
+#ifdef GPS_1PPS_PIN
+  pinMode(GPS_1PPS_PIN, INPUT);
+#endif
+#ifdef GPS_WAKEUP_PIN
+  pinMode(GPS_WAKEUP_PIN, INPUT);
+#endif
+  startUart(GPS_BAUD, GPS_RX_PIN, GPS_TX_PIN);
+}
+
+void GnssManager::startUart(uint32_t baud, int rxPin, int txPin) {
+  m_serial.end();
+  delay(20);
+  m_serial.setRxBufferSize(2048);
+  m_serial.begin(baud, SERIAL_8N1, rxPin, txPin);
+}
+
+bool GnssManager::collectTraffic(uint32_t windowMs) {
+  uint32_t start = millis();
+  bool sawBytes = false;
+  while ((uint32_t)(millis() - start) < windowMs) {
+    if (m_serial.available() > 0) {
+      sawBytes = true;
+    }
+    poll();
+    delay(2);
+  }
+  return sawBytes || m_sawSentence;
+}
+
+bool GnssManager::probeAtBaud(uint32_t baud, int rxPin, int txPin) {
+  startUart(baud, rxPin, txPin);
+  if (collectTraffic(700)) {
+    return true;
+  }
+  m_serial.write("$PCAS06,0*1B\r\n");
+  m_serial.write("$PMTK605*31\r\n");
+  m_serial.write("$PQTMVERNO*58\r\n");
+  m_serial.write("$PUBX,00*33\r\n");
+  m_serial.write("$PMTK353,1,1,1,1,1*2A\r\n");
+  m_serial.write("$PMTK314,0,1,0,1,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0*29\r\n");
+  return collectTraffic(1200);
+}
+
+bool GnssManager::probeAtStartup(Stream& serialOut) {
+  const uint32_t bauds[] = {GPS_BAUD, 115200, 38400, 57600, 19200};
+  int pins[2][2] = {{GPS_RX_PIN, GPS_TX_PIN}, {34, 12}};
+  size_t pinCount = (kExpectedGpsModule == GpsModuleKind::Ublox && !(GPS_RX_PIN == 34 && GPS_TX_PIN == 12)) ? 2 : 1;
+  for (size_t p = 0; p < pinCount; ++p) {
+    for (size_t i = 0; i < sizeof(bauds) / sizeof(bauds[0]); ++i) {
+      if (probeAtBaud(bauds[i], pins[p][0], pins[p][1])) {
+        serialOut.printf("GPS traffic detected at baud=%lu rx=%d tx=%d\n",
+                         (unsigned long)bauds[i], pins[p][0], pins[p][1]);
+        return true;
+      }
+    }
+  }
+  serialOut.println("WARNING: no GPS traffic detected during startup probe");
+  return false;
+}
+
+bool GnssManager::parseUInt2(const char* s, uint8_t& out) {
+  if (!s || !isdigit((unsigned char)s[0]) || !isdigit((unsigned char)s[1])) {
+    return false;
+  }
+  out = (uint8_t)((s[0] - '0') * 10 + (s[1] - '0'));
+  return true;
+}
+
+double GnssManager::parseNmeaCoord(const char* value, const char* hemi) {
+  if (!value || !value[0] || !hemi || !hemi[0]) {
+    return 0.0;
+  }
+  double raw = atof(value);
+  double deg = floor(raw / 100.0);
+  double minutes = raw - (deg * 100.0);
+  double result = deg + minutes / 60.0;
+  if (hemi[0] == 'S' || hemi[0] == 'W') {
+    result = -result;
+  }
+  return result;
+}
+
+int GnssManager::splitCsvPreserveEmpty(char* line, char* fields[], int maxFields) {
+  if (!line || !fields || maxFields <= 0) {
+    return 0;
+  }
+  int count = 0;
+  char* p = line;
+  fields[count++] = p;
+  while (*p && count < maxFields) {
+    if (*p == ',') {
+      *p = '\0';
+      fields[count++] = p + 1;
+    }
+    ++p;
+  }
+  return count;
+}
+
+void GnssManager::parseGga(char* fields[], int count) {
+  if (count < 10) {
+    return;
+  }
+  const int quality = atoi(fields[6]);
+  const int satsUsed = atoi(fields[7]);
+  if (satsUsed >= 0) {
+    m_state.satsUsed = satsUsed;
+  }
+  if (fields[8] && fields[8][0]) {
+    m_state.hdop = atof(fields[8]);
+    m_state.validHdop = true;
+  }
+  if (fields[9] && fields[9][0]) {
+    m_state.altitudeM = atof(fields[9]);
+    m_state.validAltitude = true;
+  }
+  if (fields[2] && fields[2][0] && fields[4] && fields[4][0]) {
+    m_state.latitude = parseNmeaCoord(fields[2], fields[3]);
+    m_state.longitude = parseNmeaCoord(fields[4], fields[5]);
+    m_state.validLocation = true;
+  }
+  if (quality > 0) {
+    m_state.validFix = true;
+    m_lastFixMs = millis();
+  } else {
+    m_state.validFix = false;
+  }
+  m_state.fixType = fixTypeFromQuality(quality, m_state.fixDimension);
+}
+
+void GnssManager::parseGsa(char* fields[], int count) {
+  if (count < 18) {
+    return;
+  }
+  const int dim = atoi(fields[2]);
+  m_state.fixDimension = dim;
+  if (count > 15 && fields[15] && fields[15][0]) {
+    m_state.pdop = atof(fields[15]);
+    m_state.validPdop = true;
+  }
+  if (count > 16 && fields[16] && fields[16][0]) {
+    m_state.hdop = atof(fields[16]);
+    m_state.validHdop = true;
+  }
+  if (count > 17 && fields[17] && fields[17][0]) {
+    m_state.vdop = atof(fields[17]);
+    m_state.validVdop = true;
+  }
+
+  int satsUsed = 0;
+  m_usedPrnCount = 0;
+  for (int i = 3; i <= 14 && i < count; ++i) {
+    if (fields[i] && fields[i][0]) {
+      ++satsUsed;
+      if (m_usedPrnCount < sizeof(m_usedPrns) / sizeof(m_usedPrns[0])) {
+        m_usedPrns[m_usedPrnCount++] = (uint8_t)atoi(fields[i]);
+      }
+    }
+  }
+  if (satsUsed > 0) {
+    m_state.satsUsed = satsUsed;
+  }
+  if (dim >= 2) {
+    m_state.validFix = true;
+    m_lastFixMs = millis();
+  }
+  m_state.fixType = fixTypeFromQuality(m_state.validFix ? 1 : 0, dim);
+}
+
+void GnssManager::clearSatelliteView() {
+  m_satCount = 0;
+  for (size_t i = 0; i < kMaxSatellites; ++i) {
+    m_satellites[i] = SatelliteInfo{};
+  }
+  m_state.gpsCount = 0;
+  m_state.galileoCount = 0;
+  m_state.glonassCount = 0;
+  m_state.beidouCount = 0;
+  m_state.navicCount = 0;
+  m_state.qzssCount = 0;
+  m_state.sbasCount = 0;
+  m_state.meanSnr = -1.0f;
+  m_state.maxSnr = 0;
+}
+
+void GnssManager::finalizeSatelliteStats() {
+  uint32_t snrSum = 0;
+  uint32_t snrCount = 0;
+  for (size_t i = 0; i < m_satCount; ++i) {
+    SatelliteInfo& sat = m_satellites[i];
+    if (!sat.valid) {
+      continue;
+    }
+    sat.usedInSolution = prnUsedInSolution(sat.prn);
+    if (strcmp(sat.talker, "GP") == 0 || strcmp(sat.talker, "GN") == 0) {
+      ++m_state.gpsCount;
+    } else if (strcmp(sat.talker, "GA") == 0) {
+      ++m_state.galileoCount;
+    } else if (strcmp(sat.talker, "GL") == 0) {
+      ++m_state.glonassCount;
+    } else if (strcmp(sat.talker, "GB") == 0 || strcmp(sat.talker, "BD") == 0) {
+      ++m_state.beidouCount;
+    } else if (strcmp(sat.talker, "GI") == 0) {
+      ++m_state.navicCount;
+    } else if (strcmp(sat.talker, "GQ") == 0) {
+      ++m_state.qzssCount;
+    } else if (strcmp(sat.talker, "GS") == 0) {
+      ++m_state.sbasCount;
+    }
+    if (sat.snr > 0) {
+      snrSum += sat.snr;
+      ++snrCount;
+      if (sat.snr > m_state.maxSnr) {
+        m_state.maxSnr = sat.snr;
+      }
+    }
+  }
+  m_state.meanSnr = snrCount > 0 ? ((float)snrSum / (float)snrCount) : -1.0f;
+}
+
+void GnssManager::parseGsv(char* fields[], int count) {
+  if (count < 4) {
+    return;
+  }
+  const int totalMsgs = atoi(fields[1]);
+  const int msgNum = atoi(fields[2]);
+  const int satsInView = atoi(fields[3]);
+  if (msgNum == 1) {
+    clearSatelliteView();
+  }
+  if (satsInView >= 0) {
+    m_state.satsInView = satsInView;
+  }
+  char talker[3];
+  copyTalker(fields[0], talker);
+  for (int i = 4; i + 3 < count && m_satCount < kMaxSatellites; i += 4) {
+    if (!fields[i] || !fields[i][0]) {
+      continue;
+    }
+    SatelliteInfo& sat = m_satellites[m_satCount++];
+    sat.valid = true;
+    sat.talker[0] = talker[0];
+    sat.talker[1] = talker[1];
+    sat.talker[2] = '\0';
+    sat.prn = (uint8_t)atoi(fields[i]);
+    sat.usedInSolution = prnUsedInSolution(sat.prn);
+    sat.elevation = (uint8_t)atoi(fields[i + 1]);
+    sat.azimuth = (uint16_t)atoi(fields[i + 2]);
+    sat.snr = (uint8_t)atoi(fields[i + 3]);
+  }
+  if (msgNum == totalMsgs) {
+    finalizeSatelliteStats();
+  }
+  m_lastGsvMs = millis();
+}
+
+bool GnssManager::prnUsedInSolution(uint8_t prn) const {
+  for (size_t i = 0; i < m_usedPrnCount; ++i) {
+    if (m_usedPrns[i] == prn) {
+      return true;
+    }
+  }
+  return false;
+}
+
+void GnssManager::parseRmc(char* fields[], int count) {
+  if (count < 10) {
+    return;
+  }
+  const char* utc = fields[1];
+  const char* status = fields[2];
+  if (status && status[0] == 'A') {
+    m_state.validFix = true;
+    m_lastFixMs = millis();
+  }
+  if (utc && strlen(utc) >= 6 && fields[9] && strlen(fields[9]) >= 6) {
+    uint8_t hh = 0, mm = 0, ss = 0, dd = 0, mo = 0, yy = 0;
+    if (parseUInt2(utc + 0, hh) && parseUInt2(utc + 2, mm) && parseUInt2(utc + 4, ss) &&
+        parseUInt2(fields[9] + 0, dd) && parseUInt2(fields[9] + 2, mo) && parseUInt2(fields[9] + 4, yy)) {
+      m_state.hour = hh;
+      m_state.minute = mm;
+      m_state.second = ss;
+      m_state.day = dd;
+      m_state.month = mo;
+      m_state.year = (uint16_t)(2000U + yy);
+      m_state.validTime = true;
+    }
+  }
+  if (fields[3] && fields[3][0] && fields[5] && fields[5][0]) {
+    m_state.latitude = parseNmeaCoord(fields[3], fields[4]);
+    m_state.longitude = parseNmeaCoord(fields[5], fields[6]);
+    m_state.validLocation = true;
+  }
+  if (fields[7] && fields[7][0]) {
+    m_state.speedMps = (float)(atof(fields[7]) * 0.514444);
+    m_state.validSpeed = true;
+  }
+  if (fields[8] && fields[8][0]) {
+    m_state.courseDeg = atof(fields[8]);
+    m_state.validCourse = true;
+  }
+}
+
+void GnssManager::parseVtg(char* fields[], int count) {
+  if (count > 1 && fields[1] && fields[1][0]) {
+    m_state.courseDeg = atof(fields[1]);
+    m_state.validCourse = true;
+  }
+  if (count > 7 && fields[7] && fields[7][0]) {
+    m_state.speedMps = (float)(atof(fields[7]) / 3.6);
+    m_state.validSpeed = true;
+  }
+}
+
+void GnssManager::parseTxt(char* fields[], int count) {
+  if (count <= 4 || !fields[4]) {
+    return;
+  }
+  String text(fields[4]);
+  text.toUpperCase();
+  if (text.indexOf("L76K") >= 0 || text.indexOf("QUECTEL") >= 0) {
+    strlcpy(m_detectedChip, "L76K", sizeof(m_detectedChip));
+  }
+}
+
+void GnssManager::processNmeaLine(char* line) {
+  if (!line || line[0] != '$') {
+    return;
+  }
+  m_sawSentence = true;
+  m_state.sawSentence = true;
+  char* star = strchr(line, '*');
+  if (star) {
+    *star = '\0';
+  }
+  char* fields[32] = {0};
+  int count = splitCsvPreserveEmpty(line, fields, 32);
+  if (count <= 0 || !fields[0]) {
+    return;
+  }
+  if (strcmp(fields[0], "$PUBX") == 0) {
+    m_seenUbloxPubx = true;
+    strlcpy(m_detectedChip, "MAX-M10S", sizeof(m_detectedChip));
+    return;
+  }
+  size_t n = strlen(fields[0]);
+  if (n < 6) {
+    return;
+  }
+  const char* type = fields[0] + (n - 3);
+  if (strcmp(type, "GGA") == 0) {
+    parseGga(fields, count);
+  } else if (strcmp(type, "GSA") == 0) {
+    parseGsa(fields, count);
+  } else if (strcmp(type, "GSV") == 0) {
+    parseGsv(fields, count);
+  } else if (strcmp(type, "RMC") == 0) {
+    parseRmc(fields, count);
+  } else if (strcmp(type, "VTG") == 0) {
+    parseVtg(fields, count);
+  } else if (strcmp(type, "TXT") == 0) {
+    parseTxt(fields, count);
+  }
+}
+
+void GnssManager::poll() {
+#ifdef GPS_1PPS_PIN
+  m_hasPps = (digitalRead(GPS_1PPS_PIN) == HIGH);
+#endif
+  while (m_serial.available() > 0) {
+    char c = (char)m_serial.read();
+    if (c == '\r') {
+      continue;
+    }
+    if (c == '\n') {
+      if (m_lineLen > 0) {
+        m_line[m_lineLen] = '\0';
+        processNmeaLine(m_line);
+        m_lineLen = 0;
+      }
+      continue;
+    }
+    if (m_lineLen + 1 < sizeof(m_line)) {
+      m_line[m_lineLen++] = c;
+    } else {
+      m_lineLen = 0;
+    }
+  }
+}
+
+GnssSample GnssManager::makeSample() const {
+  GnssSample sample = m_state;
+  sample.ppsSeen = m_hasPps;
+  sample.sampleMillis = millis();
+  if (m_lastFixMs > 0) {
+    sample.ageOfFixMs = millis() - m_lastFixMs;
+  }
+  sample.ttffMs = (m_lastFixMs > 0) ? (m_lastFixMs - m_bootMs) : 0;
+  if (sample.fixType == FixType::NoFix) {
+    if (sample.fixDimension >= 3) {
+      sample.fixType = FixType::Fix3D;
+    } else if (sample.fixDimension == 2) {
+      sample.fixType = FixType::Fix2D;
+    }
+  }
+  return sample;
+}
+
+size_t GnssManager::copySatellites(SatelliteInfo* out, size_t maxCount) const {
+  if (!out || maxCount == 0) {
+    return 0;
+  }
+  size_t n = m_satCount < maxCount ? m_satCount : maxCount;
+  for (size_t i = 0; i < n; ++i) {
+    out[i] = m_satellites[i];
+  }
+  return n;
+}
+
+const char* GnssManager::detectedChipName() const {
+  return m_detectedChip;
+}
+
+}  // namespace field_qa

exercises/18_GPS_Field_QA/lib/field_qa/GnssManager.h

@@ -0,0 +1,54 @@
+#pragma once
+
+#include <Arduino.h>
+#include "Config.h"
+#include "GnssTypes.h"
+
+namespace field_qa {
+
+class GnssManager {
+ public:
+  void begin();
+  void poll();
+  bool probeAtStartup(Stream& serialOut);
+  GnssSample makeSample() const;
+  size_t copySatellites(SatelliteInfo* out, size_t maxCount) const;
+  const char* detectedChipName() const;
+
+ private:
+  void startUart(uint32_t baud, int rxPin, int txPin);
+  bool probeAtBaud(uint32_t baud, int rxPin, int txPin);
+  bool collectTraffic(uint32_t windowMs);
+  void processNmeaLine(char* line);
+  void parseGga(char* fields[], int count);
+  void parseGsa(char* fields[], int count);
+  void parseGsv(char* fields[], int count);
+  void parseRmc(char* fields[], int count);
+  void parseVtg(char* fields[], int count);
+  void parseTxt(char* fields[], int count);
+  int splitCsvPreserveEmpty(char* line, char* fields[], int maxFields);
+  static bool parseUInt2(const char* s, uint8_t& out);
+  static double parseNmeaCoord(const char* value, const char* hemi);
+  void clearSatelliteView();
+  void finalizeSatelliteStats();
+  bool prnUsedInSolution(uint8_t prn) const;
+
+  HardwareSerial m_serial{1};
+  char m_line[160] = {0};
+  size_t m_lineLen = 0;
+  char m_detectedChip[16] = {0};
+  bool m_sawSentence = false;
+  bool m_seenUbloxPubx = false;
+  bool m_hasPps = false;
+
+  GnssSample m_state;
+  SatelliteInfo m_satellites[kMaxSatellites];
+  uint8_t m_usedPrns[16] = {0};
+  size_t m_usedPrnCount = 0;
+  size_t m_satCount = 0;
+  uint32_t m_lastGsvMs = 0;
+  uint32_t m_lastFixMs = 0;
+  uint32_t m_bootMs = 0;
+};
+
+}  // namespace field_qa

exercises/18_GPS_Field_QA/lib/field_qa/GnssTypes.cpp

@@ -0,0 +1,41 @@
+#include "GnssTypes.h"
+#include "Config.h"
+
+namespace field_qa {
+
+const char* fixTypeToString(FixType type) {
+  switch (type) {
+    case FixType::Fix2D:
+      return "2D";
+    case FixType::Fix3D:
+      return "3D";
+    case FixType::Dgps:
+      return "DGPS";
+    case FixType::RtkFloat:
+      return "RTK_FLOAT";
+    case FixType::RtkFixed:
+      return "RTK_FIXED";
+    case FixType::NoFix:
+    default:
+      return "NO_FIX";
+  }
+}
+
+const char* qualityClassForSample(const GnssSample& sample) {
+  if (!sample.validFix || sample.fixDimension < 2 || sample.satsUsed < (int)kPoorMinSatsUsed ||
+      (!sample.validHdop && sample.fixDimension < 3)) {
+    return "POOR";
+  }
+  if (sample.fixDimension < 3 || sample.satsUsed < (int)kGoodMinSatsUsed ||
+      (sample.validHdop && sample.hdop >= kMarginalHdop)) {
+    return "MARGINAL";
+  }
+  if (sample.fixDimension >= 3 && sample.satsUsed >= (int)kExcellentMinSatsUsed &&
+      sample.validHdop && sample.hdop < kExcellentHdop) {
+    return "EXCELLENT";
+  }
+  return "GOOD";
+}
+
+}  // namespace field_qa
+