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