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TinyUSB Agent Instructions

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.

Shared Ground Rules

  • Keep TinyUSB memory-safe: avoid dynamic allocation, defer ISR work to task context, and follow C99 with two-space indentation/no tabs.
  • Match file organization: core stack under src, MCU/BSP support in hw/{mcu,bsp}, examples under examples/{device,host,dual}, docs in docs, tests under test/{unit-test,fuzz,hil}.
  • Use descriptive snake_case for helpers, reserve tud_/tuh_ for public APIs, TU_ for macros, and keep headers self-contained with #if CFG_TUSB_MCU guards where needed.
  • Prefer .clang-format for C/C++ formatting, run pre-commit run --all-files before submitting, and document board/HIL coverage when applicable.
  • Commit in imperative mood, keep changes scoped, and supply PRs with linked issues plus test/build evidence.

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), or python3 tools/get_deps.py -b BOARD_NAME
  • Dependencies are cached in lib/ and hw/mcu/ directories

Build Examples

Choose ONE of these approaches:

Option 1: Individual Example with CMake and Ninja (RECOMMENDED)

cd examples/device/cdc_msc
mkdir -p build && cd build
cmake -DBOARD=raspberry_pi_pico -G Ninja -DCMAKE_BUILD_TYPE=MinSizeRel ..
cmake --build .

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

Option 2: All Examples for a Board

different folder than Option 1

cd examples/
mkdir -p build && cd build
cmake -DBOARD=raspberry_pi_pico -G Ninja -DCMAKE_BUILD_TYPE=MinSizeRel ..
cmake --build .

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

Option 3: Individual Example with Make

cd examples/device/cdc_msc
make BOARD=raspberry_pi_pico all

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

Build Options

  • Debug build:
    • CMake: -DCMAKE_BUILD_TYPE=Debug
    • Make: DEBUG=1
  • With logging:
    • CMake: -DLOG=2
    • Make: LOG=2
  • With RTT logger:
    • CMake: -DLOG=2 -DLOGGER=rtt
    • Make: LOG=2 LOGGER=rtt
  • RootHub port selection:
    • CMake: -DRHPORT_DEVICE=1
    • Make: RHPORT_DEVICE=1
  • Port speed:
    • CMake: -DRHPORT_DEVICE_SPEED=OPT_MODE_FULL_SPEED
    • Make: RHPORT_DEVICE_SPEED=OPT_MODE_FULL_SPEED

Flashing and Deployment

  • Flash with JLink:
    • CMake: ninja cdc_msc-jlink
    • Make: make BOARD=raspberry_pi_pico flash-jlink
  • Flash with OpenOCD:
    • CMake: ninja cdc_msc-openocd
    • Make: make BOARD=raspberry_pi_pico flash-openocd
  • Generate UF2:
    • CMake: ninja cdc_msc-uf2
    • Make: make BOARD=raspberry_pi_pico all uf2
  • List all targets (CMake/Ninja): ninja -t targets

Unit Testing

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

Hardware-in-the-Loop (HIL) Testing

  • Run tests on actual hardware, one of following ways:
    • test a specific board python test/hil/hil_test.py -b BOARD_NAME -B examples local.json
    • test all boards in config python test/hil/hil_test.py -B examples local.json
  • In case of error, enabled verbose mode with -v flag for detailed logs. Also try to observe script output, and try to modify hil_test.py (temporarily) to add more debug prints to pinpoint the issue.
  • Requires pre-built (all) examples for target boards (see Build Examples section 2)

take 2-5 minutes. NEVER CANCEL. Set timeout to 20+ minutes.

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

Static Analysis with PVS-Studio

  • Analyze whole project: 
    pvs-studio-analyzer analyze -f examples/cmake-build-raspberry_pi_pico/compile_commands.json -R .PVS-Studio/.pvsconfig -o pvs-report.log -j12 --dump-files --misra-cpp-version 2008 --misra-c-version 2023 --use-old-parser
  • Analyze specific source files: 
    pvs-studio-analyzer analyze -f examples/cmake-build-raspberry_pi_pico/compile_commands.json -R .PVS-Studio/.pvsconfig -S path/to/file.c -o pvs-report.log -j12 --dump-files --misra-cpp-version 2008 --misra-c-version 2023 --use-old-parser
  • Multiple specific files: 
    pvs-studio-analyzer analyze -f examples/cmake-build-raspberry_pi_pico/compile_commands.json -R .PVS-Studio/.pvsconfig -S src/file1.c -S src/file2.c -o pvs-report.log -j12 --dump-files --misra-cpp-version 2008 --misra-c-version 2023 --use-old-parser
  • Requires compile_commands.json in the build directory (generated by CMake with -DCMAKE_EXPORT_COMPILE_COMMANDS=ON)
  • Use -f option to specify path to compile_commands.json
  • Use -R .PVS-Studio/.pvsconfig to specify rule configuration file
  • Use -j12 for parallel analysis with 12 threads
  • --dump-files saves preprocessed files for debugging
  • --misra-c-version 2023 enables MISRA C:2023 checks
  • --misra-cpp-version 2008 enables MISRA C++:2008 checks
  • --use-old-parser uses legacy parser for compatibility
  • Analysis takes ~10-30 seconds depending on project size. Set timeout to 5+ minutes.
  • View results: plog-converter -a GA:1,2 -t errorfile pvs-report.log or open in PVS-Studio GUI

Validation Checklist

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 board with all example that exercises your changes, see Build Examples section (option 2)
  3. Run unit tests relevant to touched modules; add fuzz/HIL coverage when modifying parsers or protocol state machines.

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: raspberry_pi_pico - requires Pico SDK, commonly used
  • Other families: Check hw/bsp/FAMILY/boards/ for available boards

Release Instructions

DO NOT commit files automatically - only modify files and let the maintainer review before committing.

  1. Bump the release version variable at the top of tools/make_release.py.
  2. Execute python3 tools/make_release.py to refresh:
    • src/tusb_option.h (version defines)
    • repository.yml (version mapping)
    • library.json (PlatformIO version)
    • sonar-project.properties (SonarQube version)
    • docs/reference/boards.rst (generated board documentation)
    • hw/bsp/BoardPresets.json (CMake presets)
  3. Generate release notes for docs/info/changelog.rst:
    • Get commit list: git log <last-release-tag>..HEAD --oneline
    • Visit GitHub PRs for merged pull requests to understand context and gather details
    • Use GitHub tools to search/read PRs: github-mcp-server-list_pull_requests, github-mcp-server-pull_request_read
    • Extract key changes, API modifications, bug fixes, and new features from PR descriptions
    • Add new changelog entry following the existing format:
      • Version heading with equals underline (e.g., 0.20.0 followed by ======)
      • Release date in italics (e.g., *November 19, 2024*)
      • Major sections: General, API Changes, Controller Driver (DCD & HCD), Device Stack, Host Stack, Testing
      • Use bullet lists with descriptive categorization
      • Reference function names, config macros, and file paths using RST inline code (double backticks)
      • Include meaningful descriptions, not just commit messages
  4. Validation before commit:
    • Run unit tests: cd test/unit-test && ceedling test:all
    • Build at least one example: cd examples/device/cdc_msc && make BOARD=stm32f407disco all
    • Verify changed files look correct: git diff --stat
  5. Leave files unstaged for maintainer to review, modify if needed, and commit with message: Bump version to X.Y.Z
  6. After maintainer commits: Create annotated tag with git tag -a vX.Y.Z -m "Release X.Y.Z"
  7. Push commit and tag: git push origin <branch> && git push origin vX.Y.Z
  8. Create GitHub release from the tag with changelog content

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

Code Style Guidelines

General Coding Standards

  • Use C99 standard
  • Memory-safe: no dynamic allocation
  • Thread-safe: defer all interrupt events to non-ISR task functions
  • 2-space indentation, no tabs
  • Use snake_case for variables/functions
  • Use UPPER_CASE for macros and constants
  • Follow existing variable naming patterns in files you're modifying
  • Include proper header comments with MIT license
  • Add descriptive comments for non-obvious functions

Best Practices

  • When including headers, group in order: C stdlib, tusb common, drivers, classes
  • Always check return values from functions that can fail
  • Use TU_ASSERT() for error checking with return statements
  • Follow the existing code patterns in the files you're modifying

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