tinyUSB/.github/copilot-instructions.md

TinyUSB

TinyUSB is an open-source cross-platform USB Host/Device stack for embedded systems, designed to be memory-safe with no dynamic allocation and thread-safe with all interrupt events deferred to non-ISR task functions.

Always reference these instructions first and fallback to search or bash commands only when you encounter unexpected information that does not match the info here.

Working Effectively

Bootstrap and Build Setup

• Install ARM GCC toolchain: sudo apt-get update && sudo apt-get install -y gcc-arm-none-eabi
• Fetch core dependencies: python3 tools/get_deps.py -- takes <1 second. NEVER CANCEL.
• For specific board families: python3 tools/get_deps.py FAMILY_NAME (e.g., rp2040, stm32f4)
• Dependencies are cached in lib/ and hw/mcu/ directories

Build Examples

Choose ONE of these approaches:

Option 1: Individual Example with CMake (RECOMMENDED)

cd examples/device/cdc_msc
mkdir -p build && cd build
cmake -DBOARD=stm32f407disco -DCMAKE_BUILD_TYPE=MinSizeRel ..
cmake --build . -j4

-- takes 1-2 seconds. NEVER CANCEL. Set timeout to 5+ minutes.

Option 2: Individual Example with Make

cd examples/device/cdc_msc
make BOARD=stm32f407disco all

-- takes 2-3 seconds. NEVER CANCEL. Set timeout to 5+ minutes.

Option 3: All Examples for a Board

python3 tools/build.py -b BOARD_NAME

-- takes 15-20 seconds, may have some objcopy failures that are non-critical. NEVER CANCEL. Set timeout to 30+ minutes.

Unit Testing

• Install Ceedling: sudo gem install ceedling
• Run all unit tests: cd test/unit-test && ceedling -- takes 4 seconds. NEVER CANCEL. Set timeout to 10+ minutes.
• Tests use Unity framework with CMock for mocking

Documentation

• Install requirements: pip install -r docs/requirements.txt
• Build docs: cd docs && sphinx-build -b html . _build -- takes 2-3 seconds. NEVER CANCEL. Set timeout to 10+ minutes.

Code Quality and Validation

• Format code: clang-format -i path/to/file.c (uses .clang-format config)
• Check spelling: pip install codespell && codespell (uses .codespellrc config)
• Pre-commit hooks validate unit tests and code quality automatically

Validation

ALWAYS Run These After Making Changes

1. Pre-commit validation (RECOMMENDED): pre-commit run --all-files
   • Install pre-commit: pip install pre-commit && pre-commit install
   • Runs all quality checks, unit tests, spell checking, and formatting
   • Takes 10-15 seconds. NEVER CANCEL. Set timeout to 15+ minutes.
2. Build validation: Build at least one example that exercises your changes

   cd examples/device/cdc_msc
   make BOARD=stm32f407disco all
   

Manual Testing Scenarios

• Device examples: Cannot be fully tested without real hardware, but must build successfully
• Unit tests: Exercise core stack functionality - ALL tests must pass
• Build system: Must be able to build examples for multiple board families

Board Selection for Testing

• STM32F4: stm32f407disco - no external SDK required, good for testing
• RP2040: pico_sdk - requires Pico SDK, commonly used
• Other families: Check hw/bsp/FAMILY/boards/ for available boards

Common Tasks and Time Expectations

Repository Structure Quick Reference

├── src/                  # Core TinyUSB stack
│   ├── class/            # USB device classes (CDC, HID, MSC, Audio, etc.)
│   ├── portable/         # MCU-specific drivers (organized by vendor)
│   ├── device/           # USB device stack core
│   ├── host/             # USB host stack core
│   └── common/           # Shared utilities (FIFO, etc.)
├── examples/             # Example applications
│   ├── device/           # Device examples (cdc_msc, hid_generic, etc.)
│   ├── host/             # Host examples
│   └── dual/             # Dual-role examples
├── hw/bsp/               # Board Support Packages
│   └── FAMILY/boards/    # Board-specific configurations
├── test/unit-test/       # Unit tests using Ceedling
├── tools/                # Build and utility scripts
└── docs/                 # Sphinx documentation

Build Time Reference

• Dependency fetch: <1 second
• Single example build: 1-3 seconds
• Unit tests: ~4 seconds
• Documentation build: ~2.5 seconds
• Full board examples: 15-20 seconds
• Toolchain installation: 2-5 minutes (one-time)

Key Files to Know

• tools/get_deps.py: Manages dependencies for MCU families
• tools/build.py: Builds multiple examples, supports make/cmake
• src/tusb.h: Main TinyUSB header file
• src/tusb_config.h: Configuration template
• examples/device/cdc_msc/: Most commonly used example for testing
• test/unit-test/project.yml: Ceedling test configuration

Debugging Build Issues

• Missing compiler: Install gcc-arm-none-eabi package
• Missing dependencies: Run python3 tools/get_deps.py FAMILY
• Board not found: Check hw/bsp/FAMILY/boards/ for valid board names
• objcopy errors: Often non-critical in full builds, try individual example builds

Working with USB Device Classes

• CDC (Serial): src/class/cdc/ - Virtual serial port
• HID: src/class/hid/ - Human Interface Device (keyboard, mouse, etc.)
• MSC: src/class/msc/ - Mass Storage Class (USB drive)
• Audio: src/class/audio/ - USB Audio Class
• Each class has device (*_device.c) and host (*_host.c) implementations

MCU Family Support

• STM32: Largest support (F0, F1, F2, F3, F4, F7, G0, G4, H7, L4, U5, etc.)
• Raspberry Pi: RP2040, RP2350 with PIO-USB host support
• NXP: iMXRT, Kinetis, LPC families
• Microchip: SAM D/E/G/L families
• Check hw/bsp/ for complete list and docs/reference/boards.rst for details

Remember: TinyUSB is designed for embedded systems - builds are fast, tests are focused, and the codebase is optimized for resource-constrained environments.