fastled Analyze firmware crash output, decode stack traces, and diagnose embedded system failures.
$ARGUMENTS
What This Skill Does
- Crash Analysis: Parse panic handlers, guru meditation errors, hard faults, watchdog resets
- Stack Trace Decoding: Decode raw addresses to function names using ELF binaries
- Register Dump Interpretation: Analyze CPU register state at crash time
- Root Cause Identification: Correlate crash data with source code to find the bug
- Fix Recommendations: Suggest specific code changes to prevent the crash
Supported Platforms
| Platform | Crash Types |
|---|---|
| ESP32 (all variants) | Guru Meditation, LoadProhibited, StoreProhibited, InstrFetchProhibited, watchdog reset, brownout, cache errors |
| ARM Cortex-M (STM32, Teensy, nRF) | HardFault, MemManage, BusFault, UsageFault, watchdog reset |
| AVR (Arduino Uno/Mega) | Stack overflow (silent corruption), watchdog reset, undefined opcode |
| RISC-V (ESP32-C3/C6/H2) | Illegal instruction, load/store fault, breakpoint |
How To Use
With crash output
/embedded-debug
Guru Meditation Error: Core 0 panic'ed (LoadProhibited). Exception was unhandled.
Core 0 register dump:
PC : 0x400d1234 PS : 0x00060030 A0 : 0x800d5678
...
With a description
/embedded-debug Device reboots every 30 seconds, serial shows "rst:0x3 (SW_RESET)"
With a core dump
/embedded-debug Analyze the core dump from the last crash
What You'll Get
- Decoded stack trace with source file and line numbers
- Explanation of the crash type and what triggered it
- Identification of the faulty code path
- Specific fix recommendations with code examples
- Prevention strategies (stack size tuning, watchdog config, null checks)
ESP32 Crash Quick Reference
Exception Type → Root Cause
| Exception | EXCVADDR hint | Likely Root Cause |
|---|---|---|
LoadProhibited |
~0x00000000 | NULL pointer dereference (uninitialized LED strip?) |
LoadProhibited |
Other | Read from freed or out-of-bounds memory |
StoreProhibited |
Any | Write to read-only or invalid memory address |
InstrFetchProhibited |
Any | Jump to invalid/NULL function pointer or corrupt vtable |
IllegalInstruction |
Any | Stack overflow corrupting code, or corrupt heap |
IntegerDivideByZero |
N/A | Division by zero in LED index math |
Unaligned |
Any | Misaligned memory access (DMA buffer not 4-byte aligned) |
Cache disabled but cache memory range accessed |
Any | ISR accessing flash — add IRAM_ATTR to ISR function |
Key Register Meanings (ESP32 Xtensa)
| Register | Meaning |
|---|---|
PC |
Program Counter — where the crash happened |
EXCVADDR |
Address that caused the fault (NULL pointer, invalid write target) |
A1 |
Stack pointer — compare to task stack base to detect overflow |
A0 |
Return address — calling function |
ISR Violation Pattern
Symptoms: Cache disabled but cache memory range accessed or crash inside FreeRTOS API
Cause: FastLED ISR handler calling blocking or flash-accessing code.
Diagnosis: Look for crash inside xSemaphoreTake, vTaskDelay, printf, or any non-ISR-safe function.
Fix:
- Add
IRAM_ATTRto all ISR-related functions - Replace blocking calls with ISR-safe variants (
xSemaphoreGiveFromISR,xQueueSendFromISR) - Move logging out of ISR to a deferred task
Watchdog Reset Pattern
Symptoms: rst:0x7 (TG0WDT_SYS_RESET) or rst:0x8 (TG1WDT_SYS_RESET)
Cause: Task or interrupt handler not yielding — common with:
- FastLED
show()blocking on DMA in a task with watchdog enabled - High LED counts causing long encoding loops without yield
- Spinning in a loop without
vTaskDelay(0)ortaskYIELD()
Fix:
- Call
esp_task_wdt_reset()in long loops, or - Move FastLED
show()to a dedicated task exempt from watchdog, or - Reduce LED count to bring encoding time under watchdog timeout
Stack Overflow Pattern
Symptoms: StackOverflow + task name, or IllegalInstruction with A1 near stack limit
Diagnosis: Check task stack size in xTaskCreate or xTaskCreatePinnedToCore. FastLED show() with large LED arrays can use significant stack.
Fix: Increase task stack size (minimum 4096 bytes for tasks calling FastLED show with encoding)
Memory Corruption Pattern
Symptoms: IllegalInstruction at random address, corrupted register values, intermittent crashes
Diagnosis: Enable diagnostics:
// In sdkconfig or menuconfig:
CONFIG_HEAP_POISONING_COMPREHENSIVE=y
CONFIG_HEAP_TASK_TRACKING=y
CONFIG_FREERTOS_WATCHPOINT_END_OF_STACK=y
Common FastLED Cause: Writing past end of CRGB array (index out of bounds in user sketch)
Backtrace Decoding Commands
# ESP32 (Xtensa)
xtensa-esp32-elf-addr2line -pfiaC -e build/firmware.elf 0xADDR1 0xADDR2
# ESP32-S3
xtensa-esp32s3-elf-addr2line -pfiaC -e build/firmware.elf 0xADDR1
# ESP32-C3/C6 (RISC-V)
riscv32-esp-elf-addr2line -pfiaC -e build/firmware.elf 0xADDR1
# Live decode via idf.py
idf.py -p /dev/ttyUSB0 monitor