What changed from 204:

Kept all units in transport mode with reticulum.transport_enabled(true).
Removed physical blocking: SIM_PHY_BLOCK_BOB_CY=0, no per-unit block.
Removed the extra deep transmission/debug flags from platformio.ini.
Kept the 204 announcement schedule/protocol.
Removed intentional Link teardown after message cycles.
Every unit now attempts an outbound Link to every peer that announces.
Added retry health behavior: 3 Link attempts within 3 minutes, then wait for a fresh announce before trying that peer again.
Preserved substantive parseable logs: TX ANNOUNCE, RX ANNOUNCE, TX LINKREQUEST, LINK ACTIVE, TX LINK, RX LINK, retry/failure/reset events.
Updated copied helper scripts to point at 205_sustained_link.
Updated README for the new exercise behavior.

exercises/204_established_identities/scripts/handy_log_parsers.txt

@@ -0,0 +1,16 @@
+Using awk:
+
+awk -v start="20260603_080000" -v end="20260603_083000" '
+  $1 >= start && $1 < end { print  }
+' BOB_raw_20260602_191631.log | grep Hi
+ 
+  
+awk -v start="20260603_080000" -v end="20260603_083000" '
+  $1 >= start && $1 < end { print  }
+' BOB_raw_20260602_191631.log | grep 'TX LINK:'
+ 
+  
+awk -v start="20260603_080000" -v end="20260603_083000" '
+  $1 >= start && $1 < end { print  }
+' BOB_raw_20260602_191631.log | grep 'RX LINK:'
+

exercises/205_sustained_link/README.md

@@ -0,0 +1,69 @@
+# Introduction
+Exercise 205 builds on Exercise 204 established identities and LoRa Link traffic. It keeps the same identity, announce, RTC/GPS, OLED, and machine-parseable TX/RX event style, but changes the link policy for longer multi-unit field runs.
+
+All seven units, `AMY` through `GUY`, are supported. Every unit runs in transport mode and every unit attempts to open a Link to any other unit that announces.
+
+# Behavior
+
+The announce protocol is intentionally the same as the last Exercise 204 protocol:
+
+```text
+startup announce: immediate
+second announce:  ANNOUNCEMENT_2 seconds after startup, default 300
+repeat announce:  ANNOUNCEMENT_REPEAT seconds after that, default 3600
+```
+
+There is no simulated BOB/CY physical block in this exercise. `SIM_PHY_ENVELOPE` remains enabled so log records can report the physical sender slot, but `SIM_PHY_BLOCK_BOB_CY=0` for every environment.
+
+Exercise 205 does not intentionally tear down Links after a message count. A Link is reused while it remains active. If a Link becomes stale or closes, the unit clears local state and attempts to recreate the outbound Link.
+
+The outbound Link retry budget is:
+
+```text
+retry interval: 60 seconds
+failure window: 3 minutes
+max attempts:   3
+```
+
+After three failed attempts within the window, the peer is marked failed and no more Link requests are sent to that peer until another announce for that peer is received. A fresh announce resets the retry budget and starts over.
+
+# Clock Gate
+
+The unit checks the RTC and `/ex205/clock.txt` on the SD card. If the saved discipline marker is less than 24 hours old according to the RTC, LoRa/microReticulum starts immediately. If not, the OLED shows `Take outside` and serial prints `gps_gate ...` until GPS UTC/fix is available.
+
+# Log Events
+
+Substantive events retain the Exercise 204 style so multi-unit log parsing can correlate TX and RX:
+
+```text
+TX ANNOUNCE: Bob
+RX ANNOUNCE: label=Cy hash=<destination hash> phy=Cy(2)
+TX LINKREQUEST: opening link to Cy slot=19 attempt=1/3
+LINK ACTIVE: initiator link established to Cy hash=<link hash>
+RX LINK: inbound link established hash=<link hash> phy=Bob(1)
+TX LINK: Hi from Bob iter=0 to=Cy via=outbound hash=<link hash> status=2
+RX LINK: Hi from Cy iter=0 to=Bob | phy=Cy(2) RSSI=... SNR=...
+LINK RETRY: no establishment after 60000 ms; retrying Cy attempts=1/3
+LINK FAILED: peer=Cy attempts=3 window_ms=... waiting_for_announce=1
+LINK RETRY RESET: fresh announce from Cy
+```
+
+# Build, Upload, And Monitor
+
+```bash
+source /home/jlpoole/rnsenv/bin/activate
+cd /usr/local/src/microreticulum/microReticulumTbeam
+
+pio run -d exercises/205_sustained_link -e amy -e bob -e cy -e dan -e ed -e flo -e guy
+
+for env in amy bob cy dan ed flo guy
+do
+  pio run -d exercises/205_sustained_link -e "${env}" -t upload
+done
+```
+
+Monitor one unit:
+
+```bash
+pio device monitor -d exercises/205_sustained_link -e bob
+```

exercises/205_sustained_link/identities/AMY.identity

@@ -0,0 +1 @@
+ <EFBFBD>Ο Υf°TΐdΒΦλ <CEBB>ΡΚ‰BοSl>ϊw»6ΧΗ`d³Ζ¥>Z®υ6ΓΚ%Q©Μο
<07>¦W±‰	±gy―®λ…

exercises/205_sustained_link/identities/AMY.identity_info.txt

@@ -0,0 +1,3 @@
+[2026-05-28 11:26:31] Loaded Identity <c95d06fb622a80b4d80389fc7fe55d16> from ./AMY.identity
+[2026-05-28 11:26:31] Public Key  : f25adccd75eefaf9fafe5a4b22f0a16c43bf0094810c5f9279eb30ad3fd97312ba71cdd7940bb139c15949d433f8ffb57d75441d1b84a1d091b234420d22a608
+[2026-05-28 11:26:31] Private Key : Hidden

exercises/205_sustained_link/identities/BOB.identity

@@ -0,0 +1,2 @@
+àǽt½Æ$Uw™)mi$yz÷3¶Ó§ªQðwK„ïKÉ'Æù<C386>ôgÌù
+bY¶‘<EFBFBD>D6íƾ¹ˆ&ÕÜ!Òüó2ð

exercises/205_sustained_link/identities/BOB.identity_info.txt

@@ -0,0 +1,3 @@
+[2026-05-28 11:26:35] Loaded Identity <5769e13e1214e62b96e43c17bd47085e> from ./BOB.identity
+[2026-05-28 11:26:35] Public Key  : 4705bf1ab8a17cc3bb07d1fa51d4fe59dc92e4e93fd9d55124c808079d33744e894241f52583b3abc7bcaf48a5fad31554c2dee142dbbc3c4d4c5e3855d94814
+[2026-05-28 11:26:35] Private Key : Hidden

exercises/205_sustained_link/identities/CY.identity

@@ -0,0 +1,2 @@
+øß7EøbI$‡vÛp1ƒ->Ö嫵²¥GësÁ„.Ñ¥|üÝž;‹Y+­D¾­³¢;¬ôò
+¼BãPjàH`º:

exercises/205_sustained_link/identities/CY.identity_info.txt

@@ -0,0 +1,3 @@
+[2026-05-28 11:26:40] Loaded Identity <92ce7c2eb62820c2e4476308350cc69d> from ./CY.identity
+[2026-05-28 11:26:40] Public Key  : 22dc1ae58534f27562ee37edc7b072eb53502847d7aa718bd84e4baf3064867ab5945f1fc842213b10d7faeebc35d8a71903eb3cee30c112d21e39575c44131a
+[2026-05-28 11:26:40] Private Key : Hidden

exercises/205_sustained_link/identities/DAN.identity

@@ -0,0 +1 @@
+˜á¸w'
™’Úl æNñÓ´Ñ-µÉ¥¼2¥<0E>Évñu¶|,vq£GêDâ1øXϱÒyꧫëˆÜ….<2E>‚LA

exercises/205_sustained_link/identities/DAN.identity_info.txt

@@ -0,0 +1,3 @@
+[2026-05-28 11:26:44] Loaded Identity <d0524d8f1d98fc39f13772655640ea30> from ./DAN.identity
+[2026-05-28 11:26:44] Public Key  : 14483f044c5ea19c12a2c89ba539ca1ee2cea613bde7eb8d5d700058351d1067b5415b26b0ae8667c2cac4d4cc932f24b48ca727f3c5e42c614750d05e475d80
+[2026-05-28 11:26:44] Private Key : Hidden

exercises/205_sustained_link/identities/ED.identity

@@ -0,0 +1 @@
+àßðš¨L”&Žµœ£(_ÁßIär¾¤ÙßÂÐiT°S±OëKØDlàÿקÇÍ àË–x¯vœ-å•hþ@¹

exercises/205_sustained_link/identities/ED.identity_info.txt

@@ -0,0 +1,3 @@
+[2026-05-28 11:26:48] Loaded Identity <4ad998c481ff6c71d1acb8cbaf111e1f> from ./ED.identity
+[2026-05-28 11:26:48] Public Key  : c90deacc4f0ccfd552eb12205b92c31d10485ea71778bfb494a1fa6af7217c39b0a5fc1b770486cc2d0a8cb29e52ab2d44c2907e8bce6524397eabe507ff1384
+[2026-05-28 11:26:48] Private Key : Hidden

exercises/205_sustained_link/identities/FLO.identity

@@ -0,0 +1,2 @@
+<EFBFBD>
+0<03><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>5<EFBFBD><35><EFBFBD>7X<37>!##<23><>C<EFBFBD>M<EFBFBD> t{%+X<>6T!<21>ͪE<0C>M<EFBFBD>P6<50>[\^<5E>Z<EFBFBD><5A>&<26>

exercises/205_sustained_link/identities/FLO.identity_info.txt

@@ -0,0 +1,3 @@
+[2026-05-28 11:26:53] Loaded Identity <5671752180661e6af4bfe49e962f23dd> from ./FLO.identity
+[2026-05-28 11:26:53] Public Key  : 3ea3edb5198020bf0f2f87219ed2d5ea2cff6eb16116702992f14eb2a43fcd69530d1e8a8b0db60065bdbbf75332c559498cc42f171f283189a62b54f14bf28f
+[2026-05-28 11:26:53] Private Key : Hidden

exercises/205_sustained_link/identities/GUY.identity

@@ -0,0 +1 @@
+Àv<EFBFBD>p˜³{BQ5<51>ð–î ¼°Ø<C2B0>–Ýñ\ûƉoe´+o„à¯2ž<Ù­J®y•ñ'­¥äL¦2ð‹¤

exercises/205_sustained_link/identities/GUY.identity_info.txt

@@ -0,0 +1,3 @@
+[2026-05-28 11:26:57] Loaded Identity <051cfb95faa527b68368d24efb40f689> from ./GUY.identity
+[2026-05-28 11:26:57] Public Key  : cfba3c49750b6ddd3fe7a5083af447b927ffca57e2459bc16bc731aff574cd67abd4cc6198e93721c1f0bb143ddce574a629d8ecf9aa5fea530821cd1fef60f2
+[2026-05-28 11:26:57] Private Key : Hidden

exercises/205_sustained_link/platformio.ini

@@ -0,0 +1,141 @@
+; Exercise 205: sustained microReticulum Links over established identities
+
+[platformio]
+default_envs = bob
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+monitor_speed = 115200
+upload_speed = 460800
+board_build.partitions = huge_app.csv
+extra_scripts = pre:scripts/set_build_identity.py
+lib_extra_dirs =
+  ../../lib
+
+build_flags =
+  -Wall
+  -Wno-missing-field-initializers
+  -Wno-format
+  -I ../../shared/boards
+  -I ../../external/microReticulum_Firmware
+  -I ../../lib/tbeam_display/src
+  -D BOARD_MODEL=BOARD_TBEAM_S_V1
+  -D RNS_USE_FS
+  -D USTORE_USE_UNIVERSALFS
+  -D MSGPACK_USE_BOOST=OFF
+  -D MCU_ESP32
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+  -D OLED_SDA=17
+  -D OLED_SCL=18
+  -D OLED_ADDR=0x3C
+  -D RTC_I2C_ADDR=0x51
+  -D GPS_RX_PIN=9
+  -D GPS_TX_PIN=8
+  -D GPS_1PPS_PIN=6
+  -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 LORA_FREQ_MHZ=915.0
+  -D LORA_BW_KHZ=125.0
+  -D LORA_SF=7
+  -D LORA_CR=5
+  -D LORA_SYNC_WORD=0x12
+  -D LORA_TX_POWER_DBM=14
+  -D USTORE_MAX_VALUE_LEN=1200
+  -D SIM_PHY_ENVELOPE=1
+  -D SIM_PHY_BLOCK_BOB_CY=0
+  -D ANNOUNCEMENT_2=300
+  -D ANNOUNCEMENT_REPEAT=3600
+; Live announces are enough for this single-hop field exercise. Do not define
+; RNS_PERSIST_PATHS here: the LittleFS-backed path_store compactor can leave an
+; active segment FD open while unlinking /path_store_*.dat on ESP32.
+
+lib_deps =
+  Wire
+  SD
+  olikraus/U8g2@^2.36.4
+  lewisxhe/XPowersLib@0.3.3
+  ArduinoJson@^7.4.2
+  MsgPack@^0.4.2
+  jgromes/RadioLib@^7.0.0
+  https://github.com/attermann/Crypto.git
+  https://github.com/attermann/microStore.git
+  microReticulum=symlink:///usr/local/src/microreticulum/microReticulum
+
+[env:amy]
+extends = env
+upload_port = /dev/ttytAMY
+monitor_port = /dev/ttytAMY
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"AMY\"
+  -D NODE_LABEL=\"Amy\"
+  -D NODE_SLOT_INDEX=0
+
+[env:bob]
+extends = env
+upload_port = /dev/ttytBOB
+monitor_port = /dev/ttytBOB
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"BOB\"
+  -D NODE_LABEL=\"Bob\"
+  -D NODE_SLOT_INDEX=1
+
+[env:cy]
+extends = env
+upload_port = /dev/ttytCY
+monitor_port = /dev/ttytCY
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"CY\"
+  -D NODE_LABEL=\"Cy\"
+  -D NODE_SLOT_INDEX=2
+
+[env:dan]
+extends = env
+upload_port = /dev/ttytDAN
+monitor_port = /dev/ttytDAN
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"DAN\"
+  -D NODE_LABEL=\"Dan\"
+  -D NODE_SLOT_INDEX=3
+
+[env:ed]
+extends = env
+upload_port = /dev/ttytED
+monitor_port = /dev/ttytED
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"ED\"
+  -D NODE_LABEL=\"Ed\"
+  -D NODE_SLOT_INDEX=4
+
+[env:flo]
+extends = env
+upload_port = /dev/ttytFLO
+monitor_port = /dev/ttytFLO
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"FLO\"
+  -D NODE_LABEL=\"Flo\"
+  -D NODE_SLOT_INDEX=5
+
+[env:guy]
+extends = env
+upload_port = /dev/ttytGUY
+monitor_port = /dev/ttytGUY
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"GUY\"
+  -D NODE_LABEL=\"Guy\"
+  -D NODE_SLOT_INDEX=6

exercises/205_sustained_link/scripts/handy_log_parsers.txt

@@ -0,0 +1,16 @@
+Using awk:
+
+awk -v start="20260603_080000" -v end="20260603_083000" '
+  $1 >= start && $1 < end { print  }
+' BOB_raw_20260602_191631.log | grep Hi
+ 
+  
+awk -v start="20260603_080000" -v end="20260603_083000" '
+  $1 >= start && $1 < end { print  }
+' BOB_raw_20260602_191631.log | grep 'TX LINK:'
+ 
+  
+awk -v start="20260603_080000" -v end="20260603_083000" '
+  $1 >= start && $1 < end { print  }
+' BOB_raw_20260602_191631.log | grep 'RX LINK:'
+

exercises/205_sustained_link/scripts/load_only.sh

@@ -0,0 +1,184 @@
+#!/bin/bash
+#
+# 20260602 ChatGPT
+# $Id$
+# $HeadURL$
+#
+# Example command lines:
+#
+#   ./load_only.sh --tbeams "CY"
+#   ./load_only.sh --tbeams "DAN"
+#   ./load_only.sh --tbeams "BOB"
+#   ./load_only.sh --tbeams "BOB CY DAN"
+#   ./load_only.sh --tbeams "bob,cy,dan"
+#
+# If pio/platformio is not in PATH:
+#
+#   ./load_only.sh --pio-bin "$HOME/pioenv/bin/platformio" --tbeams "DAN"
+#
+
+set -euo pipefail
+
+EXERCISE="/usr/local/src/microreticulum/microReticulumTbeam/exercises/205_sustained_link"
+REMOTE_HOST="ryzdesk"
+TBEAMS_RAW=""
+PIO_BIN=""
+
+usage() {
+    cat <<'EOF'
+Usage:
+  ./load_only.sh --tbeams "CY"
+  ./load_only.sh --tbeams "BOB CY DAN"
+  ./load_only.sh --tbeams "bob,cy,dan"
+
+Required:
+  --tbeams      One or more of: AMY BOB CY DAN ED FLO GUY
+
+Optional:
+  --pio-bin     Full path to pio/platformio executable
+  --exercise    PlatformIO project directory
+  --remote      Remote build host, default: ryzdesk
+EOF
+}
+
+while [ "$#" -gt 0 ]
+do
+    case "$1" in
+        --tbeams)
+            shift
+            [ "$#" -gt 0 ] || { echo "ERROR: --tbeams requires a value" >&2; exit 1; }
+            TBEAMS_RAW="$1"
+            ;;
+        --pio-bin)
+            shift
+            [ "$#" -gt 0 ] || { echo "ERROR: --pio-bin requires a value" >&2; exit 1; }
+            PIO_BIN="$1"
+            ;;
+        --exercise)
+            shift
+            [ "$#" -gt 0 ] || { echo "ERROR: --exercise requires a value" >&2; exit 1; }
+            EXERCISE="$1"
+            ;;
+        --remote)
+            shift
+            [ "$#" -gt 0 ] || { echo "ERROR: --remote requires a value" >&2; exit 1; }
+            REMOTE_HOST="$1"
+            ;;
+        -h|--help)
+            usage
+            exit 0
+            ;;
+        *)
+            echo "ERROR: unknown option: $1" >&2
+            usage >&2
+            exit 1
+            ;;
+    esac
+    shift
+done
+
+if [ -z "$TBEAMS_RAW" ]; then
+    echo "ERROR: missing required option --tbeams" >&2
+    usage >&2
+    exit 1
+fi
+
+if [ ! -d "$EXERCISE" ]; then
+    echo "ERROR: EXERCISE directory not found: $EXERCISE" >&2
+    exit 1
+fi
+
+if [ ! -f "$EXERCISE/platformio.ini" ]; then
+    echo "ERROR: platformio.ini not found under: $EXERCISE" >&2
+    exit 1
+fi
+
+if [ -n "$PIO_BIN" ]; then
+    if [ ! -x "$PIO_BIN" ]; then
+        echo "ERROR: --pio-bin is not executable: $PIO_BIN" >&2
+        exit 1
+    fi
+else
+    if command -v pio >/dev/null 2>&1; then
+        PIO_BIN="$(command -v pio)"
+    elif command -v platformio >/dev/null 2>&1; then
+        PIO_BIN="$(command -v platformio)"
+    else
+        echo "ERROR: cannot find pio or platformio in PATH" >&2
+        echo "       Try: --pio-bin \"\$HOME/pioenv/bin/platformio\"" >&2
+        exit 1
+    fi
+fi
+
+echo "EXERCISE:    $EXERCISE"
+echo "REMOTE_HOST: $REMOTE_HOST"
+echo "PIO_BIN:     $PIO_BIN"
+echo
+
+#
+# Accept either:
+#   "BOB CY DAN"
+#   "bob,cy,dan"
+#
+TBEAMS_NORMALIZED="$(echo "$TBEAMS_RAW" | tr ',' ' ')"
+
+for env_raw in $TBEAMS_NORMALIZED
+do
+    env="$(echo "$env_raw" | tr '[:upper:]' '[:lower:]')"
+    ENV="$(echo "$env" | tr '[:lower:]' '[:upper:]')"
+
+    case "$env" in
+        amy|bob|cy|dan|ed|flo|guy)
+            ;;
+        *)
+            echo "ERROR: invalid T-Beam name: $env_raw" >&2
+            echo "       Allowed names: AMY BOB CY DAN ED FLO GUY" >&2
+            exit 1
+            ;;
+    esac
+
+    dev="/dev/ttyt${ENV}"
+    remote_build_dir="${EXERCISE}/.pio/build/${env}"
+    local_build_dir="${EXERCISE}/.pio/build/${env}"
+
+    if [ ! -e "$dev" ]; then
+        echo "ERROR: expected device not found for $ENV: $dev" >&2
+        exit 1
+    fi
+
+    if ! ssh "$REMOTE_HOST" "test -d '$remote_build_dir'"; then
+        echo "ERROR: remote build directory missing on ${REMOTE_HOST}: $remote_build_dir" >&2
+        exit 1
+    fi
+
+    if [ ! -d "$local_build_dir" ]; then
+        echo "Creating missing local build directory: $local_build_dir"
+        mkdir -p "$local_build_dir" || {
+            echo "ERROR: failed to create $local_build_dir" >&2
+            exit 1
+        }
+    fi
+
+    echo "===== copy built artifact tree for $env from $REMOTE_HOST ====="
+    rsync -a \
+      "${REMOTE_HOST}:${remote_build_dir}/" \
+      "${local_build_dir}/"
+
+    if [ ! -f "${local_build_dir}/firmware.bin" ] &&
+       [ ! -f "${local_build_dir}/firmware.elf" ]; then
+        echo "ERROR: copied build tree does not appear to contain firmware output:" >&2
+        echo "       $local_build_dir" >&2
+        exit 1
+    fi
+
+    echo "===== loader-only upload $ENV on $dev ====="
+    "$PIO_BIN" run \
+      -d "$EXERCISE" \
+      -e "$env" \
+      -t nobuild \
+      -t upload \
+      --upload-port "$dev"
+
+    echo "===== finished loader-only upload for $ENV ====="
+    echo
+done

exercises/205_sustained_link/scripts/pull_build_from_ryzdesk.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+# $Header$
+# $HeadURL$
+
+set -e
+
+EXERCISE="/usr/local/src/microreticulum/microReticulumTbeam/exercises/205_sustained_link"
+
+for env in amy bob cy dan ed flo guy
+do
+    ENV="$(echo "$env" | tr '[:lower:]' '[:upper:]')"
+
+    echo "===== copy artifact $env from ryzdesk ====="
+    rsync -a \
+      "ryzdesk:${EXERCISE}/.pio/build/${env}/" \
+      "${EXERCISE}/.pio/build/${env}/"
+
+    echo "===== upload $env / $ENV ====="
+    pio run \
+      -d "$EXERCISE" \
+      -e "$env" \
+      -t nobuild \
+      -t upload \
+      --upload-port "/dev/ttyt${ENV}"
+done

exercises/205_sustained_link/scripts/pull_only_from_ryzdesk.sh

@@ -0,0 +1,26 @@
+#!/bin/bash
+# $Header$
+# $HeadURL$
+
+set -e
+
+EXERCISE="/usr/local/src/microreticulum/microReticulumTbeam/exercises/205_sustained_link"
+
+for env in amy bob cy dan ed flo guy
+do
+    ENV="$(echo "$env" | tr '[:lower:]' '[:upper:]')"
+    local_build_dir="${EXERCISE}/.pio/build/${env}"
+
+    if [ ! -d "$local_build_dir" ]; then
+        echo "Creating missing local build directory: $local_build_dir"
+        mkdir -p "$local_build_dir" || {
+            echo "ERROR: failed to create $local_build_dir" >&2
+            exit 1
+        }
+    fi
+    echo "===== copy artifact $env from ryzdesk ====="
+    rsync -a \
+      "ryzdesk:${EXERCISE}/.pio/build/${env}/" \
+      "${EXERCISE}/.pio/build/${env}/"
+
+done

exercises/205_sustained_link/scripts/set_build_identity.py

@@ -0,0 +1,23 @@
+import binascii
+import time
+from pathlib import Path
+
+Import("env")
+
+pioenv = env.subst("$PIOENV").upper()
+identity_path = Path(env.subst("$PROJECT_DIR")) / "identities" / f"{pioenv}.identity"
+
+if not identity_path.exists():
+    raise RuntimeError(f"Missing identity file for {pioenv}: {identity_path}")
+
+identity_hex = binascii.hexlify(identity_path.read_bytes()).decode("ascii")
+epoch = int(time.time())
+utc_tag = time.strftime("%Y%m%d_%H%M%S", time.gmtime(epoch))
+
+env.Append(
+    CPPDEFINES=[
+        ("LOCAL_IDENTITY_HEX", f'\\"{identity_hex}\\"'),
+        ("FW_BUILD_EPOCH", str(epoch)),
+        ("FW_BUILD_UTC", f'\\"{utc_tag}\\"'),
+    ]
+)

exercises/205_sustained_link/src/TBeamSupremeLoRaInterface.cpp

@@ -0,0 +1,245 @@
+#include "TBeamSupremeLoRaInterface.h"
+
+#include <Cryptography/Random.h>
+#include <Log.h>
+
+#include <string.h>
+
+#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
+#ifndef NODE_SLOT_INDEX
+#define NODE_SLOT_INDEX 255
+#endif
+#ifndef SIM_PHY_ENVELOPE
+#define SIM_PHY_ENVELOPE 0
+#endif
+#ifndef SIM_PHY_BLOCK_BOB_CY
+#define SIM_PHY_BLOCK_BOB_CY 0
+#endif
+
+using namespace RNS;
+
+TBeamSupremeLoRaInterface::TBeamSupremeLoRaInterface(const char* name) : InterfaceImpl(name) {
+  _IN = true;
+  _OUT = true;
+  _bitrate = (double)LORA_SF * ((4.0 / LORA_CR) / (pow(2, LORA_SF) / LORA_BW_KHZ)) * 1000.0;
+  _HW_MTU = (uint16_t)(LORA_MAX_PAYLOAD * 2);
+}
+
+TBeamSupremeLoRaInterface::~TBeamSupremeLoRaInterface() {
+  stop();
+  delete _radio;
+  delete _module;
+}
+
+bool TBeamSupremeLoRaInterface::start() {
+  _online = false;
+  INFO("LoRa initializing for T-Beam Supreme...");
+
+  SPI.begin(LORA_SCK, LORA_MISO, LORA_MOSI, LORA_CS);
+  _module = new Module(LORA_CS, LORA_DIO1, LORA_RESET, LORA_BUSY, SPI);
+  _radio = new SX1262(_module);
+
+  int state = _radio->begin(
+      LORA_FREQ_MHZ,
+      LORA_BW_KHZ,
+      LORA_SF,
+      LORA_CR,
+      LORA_SYNC_WORD,
+      LORA_TX_POWER_DBM);
+
+  if (state != RADIOLIB_ERR_NONE) {
+    ERRORF("LoRa init failed, code %d", state);
+    return false;
+  }
+
+  state = _radio->startReceive();
+  if (state != RADIOLIB_ERR_NONE) {
+    ERRORF("LoRa startReceive failed, code %d", state);
+    return false;
+  }
+
+  _online = true;
+  INFO("LoRa init succeeded.");
+  return true;
+}
+
+void TBeamSupremeLoRaInterface::stop() {
+  if (_radio) {
+    _radio->standby();
+  }
+  _online = false;
+}
+
+void TBeamSupremeLoRaInterface::loop() {
+  if (!_online || !_radio) {
+    return;
+  }
+
+  if (!_radio->checkIrq(RADIOLIB_IRQ_RX_DONE)) {
+    return;
+  }
+
+  int len = _radio->getPacketLength();
+  uint8_t rx_buf[RADIO_MAX_PAYLOAD];
+  int state = _radio->readData(rx_buf, len);
+
+  if (state == RADIOLIB_ERR_NONE) {
+    _last_rssi = _radio->getRSSI();
+    _last_snr = _radio->getSNR();
+
+    uint8_t physical_tx = 255;
+    if (!unpack_frame(rx_buf, len, physical_tx)) {
+      _radio->startReceive();
+      return;
+    }
+    if (len <= 1) {
+      _radio->startReceive();
+      return;
+    }
+
+    uint8_t header = rx_buf[0];
+    uint8_t seq = packet_sequence(header);
+
+    if (is_split_packet(header)) {
+      if (_rx_seq == SEQ_UNSET || _rx_seq != seq) {
+        _rx_seq = seq;
+        _rx_buffer.clear();
+        _rx_buffer.append(rx_buf + 1, len - 1);
+      } else {
+        _rx_buffer.append(rx_buf + 1, len - 1);
+        _rx_seq = SEQ_UNSET;
+        on_incoming(_rx_buffer);
+      }
+    } else {
+      if (_rx_seq != SEQ_UNSET) {
+        _rx_buffer.clear();
+        _rx_seq = SEQ_UNSET;
+      }
+      _rx_buffer.clear();
+      _rx_buffer.append(rx_buf + 1, len - 1);
+      on_incoming(_rx_buffer);
+    }
+  } else if (state != RADIOLIB_ERR_NONE) {
+    DEBUGF("LoRa readData failed, code %d", state);
+  }
+
+  _radio->startReceive();
+}
+
+int TBeamSupremeLoRaInterface::transmit_frame(uint8_t header, const uint8_t* payload, size_t payload_len) {
+  uint8_t tx_buf[RADIO_MAX_PAYLOAD];
+#if SIM_PHY_ENVELOPE
+  tx_buf[0] = PHY_MAGIC_0;
+  tx_buf[1] = PHY_MAGIC_1;
+  tx_buf[2] = PHY_VERSION;
+  tx_buf[3] = (uint8_t)NODE_SLOT_INDEX;
+  tx_buf[PHY_ENVELOPE_LEN] = header;
+  memcpy(tx_buf + PHY_ENVELOPE_LEN + 1, payload, payload_len);
+  return _radio->transmit(tx_buf, PHY_ENVELOPE_LEN + 1 + payload_len);
+#else
+  tx_buf[0] = header;
+  memcpy(tx_buf + 1, payload, payload_len);
+  return _radio->transmit(tx_buf, 1 + payload_len);
+#endif
+}
+
+bool TBeamSupremeLoRaInterface::unpack_frame(uint8_t* frame, int& len, uint8_t& physical_tx) {
+#if SIM_PHY_ENVELOPE
+  if (len < PHY_ENVELOPE_LEN + 1) {
+    ++_phy_bad_frames;
+    DEBUGF("SIM PHY malformed: short frame len=%d", len);
+    return false;
+  }
+  if (frame[0] != PHY_MAGIC_0 || frame[1] != PHY_MAGIC_1 || frame[2] != PHY_VERSION) {
+    ++_phy_bad_frames;
+    DEBUGF("SIM PHY malformed: bad envelope len=%d", len);
+    return false;
+  }
+  physical_tx = frame[3];
+  if (should_drop_physical_tx(physical_tx)) {
+    ++_phy_blocked_frames;
+    Serial.printf("SIM PHY DROP: rx=%u tx=%u len=%d blocked=%lu\r\n",
+                  (unsigned)NODE_SLOT_INDEX,
+                  (unsigned)physical_tx,
+                  len,
+                  (unsigned long)_phy_blocked_frames);
+    DEBUGF("SIM PHY DROP: rx=%u tx=%u len=%d",
+           (unsigned)NODE_SLOT_INDEX,
+           (unsigned)physical_tx,
+           len);
+    return false;
+  }
+  _last_physical_tx = physical_tx;
+  ++_phy_rx_frames;
+  len -= PHY_ENVELOPE_LEN;
+  memmove(frame, frame + PHY_ENVELOPE_LEN, len);
+  return true;
+#else
+  (void)frame;
+  physical_tx = 255;
+  _last_physical_tx = physical_tx;
+  ++_phy_rx_frames;
+  return true;
+#endif
+}
+
+bool TBeamSupremeLoRaInterface::should_drop_physical_tx(uint8_t physical_tx) {
+#if SIM_PHY_BLOCK_BOB_CY
+  const uint8_t local = (uint8_t)NODE_SLOT_INDEX;
+  return (local == 1U && physical_tx == 2U) || (local == 2U && physical_tx == 1U);
+#else
+  (void)physical_tx;
+  return false;
+#endif
+}
+
+void TBeamSupremeLoRaInterface::send_outgoing(const Bytes& data) {
+  if (!_online || !_radio) {
+    return;
+  }
+
+  try {
+    uint8_t rand_nibble = (uint8_t)(Cryptography::randomnum(256)) & 0xF0;
+
+    if ((int)data.size() <= LORA_MAX_PAYLOAD) {
+      int state = transmit_frame(rand_nibble, data.data(), data.size());
+      if (state != RADIOLIB_ERR_NONE) {
+        ERRORF("LoRa transmit failed, code %d", state);
+      }
+    } else {
+      uint8_t seq = (_tx_seq_ctr++) & HEADER_SEQ_MASK;
+      uint8_t split_header = rand_nibble | HEADER_SPLIT | seq;
+
+      int state = transmit_frame(split_header, data.data(), LORA_MAX_PAYLOAD);
+      if (state != RADIOLIB_ERR_NONE) {
+        ERRORF("LoRa transmit part 1 failed, code %d", state);
+      }
+
+      size_t remainder = data.size() - LORA_MAX_PAYLOAD;
+      state = transmit_frame(split_header, data.data() + LORA_MAX_PAYLOAD, remainder);
+      if (state != RADIOLIB_ERR_NONE) {
+        ERRORF("LoRa transmit part 2 failed, code %d", state);
+      }
+    }
+
+    _radio->startReceive();
+    InterfaceImpl::handle_outgoing(data);
+  } catch (const std::exception& e) {
+    ERRORF("LoRa transmit exception: %s", e.what());
+  }
+}
+
+void TBeamSupremeLoRaInterface::on_incoming(const Bytes& data) {
+  InterfaceImpl::handle_incoming(data);
+}

exercises/205_sustained_link/src/TBeamSupremeLoRaInterface.h

@@ -0,0 +1,63 @@
+#pragma once
+
+#include <Bytes.h>
+#include <Interface.h>
+
+#include <Arduino.h>
+#include <RadioLib.h>
+#include <SPI.h>
+
+class TBeamSupremeLoRaInterface : public RNS::InterfaceImpl {
+public:
+  explicit TBeamSupremeLoRaInterface(const char* name = "TBeamSupremeLoRa");
+  ~TBeamSupremeLoRaInterface() override;
+
+  bool start() override;
+  void stop() override;
+  void loop() override;
+
+  float last_rssi() const { return _last_rssi; }
+  float last_snr() const { return _last_snr; }
+  uint8_t last_physical_tx() const { return _last_physical_tx; }
+  uint32_t phy_rx_frames() const { return _phy_rx_frames; }
+  uint32_t phy_blocked_frames() const { return _phy_blocked_frames; }
+  uint32_t phy_bad_frames() const { return _phy_bad_frames; }
+
+private:
+  void send_outgoing(const RNS::Bytes& data) override;
+  void on_incoming(const RNS::Bytes& data);
+  int transmit_frame(uint8_t header, const uint8_t* payload, size_t payload_len);
+  bool unpack_frame(uint8_t* frame, int& len, uint8_t& physical_tx);
+  static bool should_drop_physical_tx(uint8_t physical_tx);
+
+  static constexpr uint8_t HEADER_SPLIT = 0x08;
+  static constexpr uint8_t HEADER_SEQ_MASK = 0x07;
+  static constexpr uint8_t SEQ_UNSET = 0xFF;
+  static constexpr int RADIO_MAX_PAYLOAD = 255;
+#if defined(SIM_PHY_ENVELOPE) && SIM_PHY_ENVELOPE
+  static constexpr uint8_t PHY_MAGIC_0 = 0xC2;
+  static constexpr uint8_t PHY_MAGIC_1 = 0x04;
+  static constexpr uint8_t PHY_VERSION = 0x01;
+  static constexpr int PHY_ENVELOPE_LEN = 4;
+  static constexpr int LORA_MAX_PAYLOAD = RADIO_MAX_PAYLOAD - PHY_ENVELOPE_LEN - 1;
+#else
+  static constexpr int PHY_ENVELOPE_LEN = 0;
+  static constexpr int LORA_MAX_PAYLOAD = RADIO_MAX_PAYLOAD - 1;
+#endif
+
+  static bool is_split_packet(uint8_t header) { return (header & HEADER_SPLIT) != 0; }
+  static uint8_t packet_sequence(uint8_t header) { return header & HEADER_SEQ_MASK; }
+
+  RNS::Bytes _rx_buffer;
+  uint8_t _rx_seq = SEQ_UNSET;
+  uint8_t _tx_seq_ctr = 0;
+  uint8_t _last_physical_tx = 255;
+  uint32_t _phy_rx_frames = 0;
+  uint32_t _phy_blocked_frames = 0;
+  uint32_t _phy_bad_frames = 0;
+  float _last_rssi = 0.0f;
+  float _last_snr = 0.0f;
+
+  Module* _module = nullptr;
+  SX1262* _radio = nullptr;
+};