firmware-core

name	firmware-core
description	Core firmware context for the Megahub ESP32 project. Use when working on PlatformIO configuration, build scripts, library structure, main.cpp, or general ESP32 firmware development. Covers build system, project structure, common pitfalls, and debugging.

Firmware Core — Megahub ESP32

Build System

PlatformIO configuration — see platformio.ini:

• Environment: esp-wrover-kit
• Framework: Arduino + ESP-IDF hybrid
• Partition table: custom_4mb_noota.csv (no OTA, maximizes app partition)
• Pre-build scripts (in order):
  1. gitversion.py — injects git hash into firmware
  2. buildfrontend.py — runs npm run build for the selected frontend mode
  3. embedfiles.py — gzips and embeds frontend files into firmware as C arrays

Serial monitor: 115200 baud. Log level controlled by CORE_DEBUG_LEVEL (currently 2).

Logging macros — always use these, never Serial.print():

INFO("Free heap: %d bytes", ESP.getFreeHeap());
WARN("Something unexpected: %d", value);
ERROR("Critical failure in %s", __func__);

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Library Structure

lib/
  btremote/       BLE server (Web Bluetooth API) + Classic BT HID host (gamepads)
  commands/       Command processing system — all device operations use this pattern
  configuration/  WiFi & system configuration persistence
  hubwebserver/   HTTP server using PsychicHttp library
  imu/            MPU6050 IMU — I²C, requires proper init sequence
  lpfuart/        LEGO Powered Up UART protocol implementation
  lua/            Lua 5.4 interpreter (embedded, constrained memory)
  megahub/        Main application — wires all libraries together
  portstatus/     Port status tracking and JSON serialization
  inputdevices/   Gamepad/HID input device abstraction
  statusmonitor/  System health monitoring (heap, tasks)

Key Architecture: Command Pattern

All device operations go through lib/commands/. This provides:

• Serialization of requests from multiple sources (BLE, Web)
• Consistent error handling and response formatting
• Command queuing for rate-limited devices

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Common Pitfalls

Pitfall	Fix
BLE race condition	Use proper task synchronization (mutex/queue)
Stack overflow	Use uxTaskGetStackHighWaterMark(), move large vars to heap
String heap fragmentation	Use std::string::reserve() or fixed buffers
Blocking in BLE callback	Post to a queue, handle in application task
Lua crash	Wrap ALL Lua execution in lua_pcall()
LEGO device timeout	Send keepalive commands, handle wake-up sequence
IMU init failure	Always include required delays in MPU6050 init sequence
Memory leak	Every new/malloc must have matching delete/free

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Debugging

pio device monitor --baud 115200   # Serial monitor
pio test                           # Run unit tests
pio run                            # Build only (no upload)

Crash analysis: Enable ESP32 exception decoder in PlatformIO. Stack traces decode to source lines.

Runtime monitoring:

INFO("Free heap: %d bytes, Free PSRAM: %d bytes",
     ESP.getFreeHeap(), ESP.getFreePsram());
INFO("Task stack HWM: %d words", uxTaskGetStackHighWaterMark(NULL));

Known heap budget (from real device logs):

• After IMU init: ~170KB free heap
• After Lua state creation: ~140KB free heap
• After BT stack start: ~75KB free heap
• PSRAM: ~4.1MB available (confirmed present on this board)