Measurement units: bytes (STM32F446 is 32-bit; configSTACK_DEPTH_TYPE
word count × 4).
Instrument: uxTaskGetStackHighWaterMark() read at 10 s cadence.
Soak duration: 48 h nominal flight-mode.
Reporting: stack minimum free bytes per task, downlinked with
housekeeping telemetry APID 0x010.
Each task’s init path writes a known sentinel pattern through the
entire stack (FreeRTOS default on configCHECK_FOR_STACK_OVERFLOW
= 1). A periodic probe walks the stack looking for the first word
that still holds the sentinel — the watermark. A deep-recursion
event trims the watermark downward permanently; no “healing” is
possible once a push overwrote the sentinel, so the watermark is
a true worst-case witness across the whole soak.
| Task | Allocated (B) | HWM observed (B) | Margin (%) | Status |
|---|---|---|---|---|
| SensorTask | 2048 | TBD | TBD | ⏳ |
| TelemetryTask | 2048 | TBD | TBD | ⏳ |
| CommTask | 4096 | TBD | TBD | ⏳ |
| ADCSTask | 4096 | TBD | TBD | ⏳ |
| WatchdogTask | 1024 | TBD | TBD | ⏳ |
| PayloadTask | 2048 | TBD | TBD | ⏳ |
| IDLE (FreeRTOS) | 256 | TBD | TBD | ⏳ |
| Timer (FreeRTOS) | 512 | TBD | TBD | ⏳ |
Margin: (allocated − HWM) / allocated * 100.
Status legend: ✅ ≥ 30 % free / ⚠ 15–30 % / ❌ < 15 % (bump stack) / ⏳ not yet measured.
Sizes from firmware/stm32/Core/Inc/main.h:
| Define | Value (words) | Bytes |
|---|---|---|
SENSOR_TASK_STACK_SIZE |
512 | 2048 |
TELEMETRY_TASK_STACK_SIZE |
512 | 2048 |
COMM_TASK_STACK_SIZE |
1024 | 4096 |
ADCS_TASK_STACK_SIZE |
1024 | 4096 |
WATCHDOG_TASK_STACK_SIZE |
256 | 1024 |
PAYLOAD_TASK_STACK_SIZE |
512 | 2048 |
configTOTAL_HEAP_SIZE (heap_4) is sized to accommodate the sum
of task control blocks + queue storage; tracked separately in
heap_usage.md.
FreeRTOSConfig.h: configCHECK_FOR_STACK_OVERFLOW = 2
(method-2 pattern check) and INCLUDE_uxTaskGetStackHighWaterMark = 1.vApplicationStackOverflowHook() implemented in
firmware/stm32/Core/Src/error_handler.c to raise
FAULT_STACK_OVERFLOW on hook entry (primary action REBOOT per
docs/reliability/fdir.md).