TinyUSB Agent Instructions

TinyUSB is a cross-platform USB Host/Device stack for embedded systems: memory-safe (no dynamic allocation) and thread-safe (ISR events deferred to task context).

Reference these instructions first; fall back to search/bash only when reality diverges.

Behavioral Guidelines

Bias toward caution over speed. For trivial tasks, use judgment.

  • Think first — state assumptions; ask if unclear; present alternatives instead of picking silently.
  • Simplicity — no features, abstractions, flexibility, or error handling beyond what was asked. If 200 lines could be 50, rewrite.
  • Surgical changes — touch only what the task requires; match existing style; don't refactor working code; mention unrelated dead code rather than deleting it. Remove only orphans your changes created.
  • Goal-driven — turn tasks into verifiable goals (“write failing test, make it pass”). For multi-step work, state a brief step → verify plan.
  • Worktrees — default to a git worktree for any branch or multi-step work; never switch the shared primary checkout's branch. Sessions run concurrently: switching the primary checkout mid-flight disrupts other sessions and can silently point a review, build, or commit at the wrong diff. Only trivial one-shot fixes may skip this. Standard location: .worktrees/<branch-name> at the repo root (gitignored), e.g. git worktree add .worktrees/my-branch -b my-branch. In a new worktree, symlink the dependency dirs (lib/*, hw/mcu/*, tools/linkermap — the keys of deps_all in tools/get_deps.py) to the primary checkout instead of re-cloning them; only if the branch needs a different dep revision, replace that one symlink with a real dir and run get_deps.py for it.

Ground Rules

  • Language/style: C99, 2-space indent (no tabs), snake_case helpers, UPPER_CASE macros. Public APIs use tud_/tuh_; macros use TU_. Headers self-contained with #if CFG_TUSB_MCU guards.
  • Safety: no dynamic allocation; defer ISR work to task context; use TU_ASSERT() for error checks; always check return values; include order: C stdlib → tusb common → drivers → classes.
  • Layout: src/ core, hw/{mcu,bsp}/ MCU+BSP, examples/{device,host,dual}/, test/{unit-test,fuzz,hil}/, docs/, tools/.
  • Commits/PRs: imperative mood, scoped changes, link issues, include test/build evidence. After opening a PR, drive it to green: address automated review comments (Copilot/Codex/Claude) and fix failing CI, pushing follow-ups until checks pass and threads resolve. Useful: gh pr checks <num> --watch, gh pr view <num> --comments.
  • Formatting/lint: clang-format (.clang-format), codespell (.codespellrc); run pre-commit run --all-files before submitting.

Bootstrap

sudo apt-get install -y gcc-arm-none-eabi          # ARM toolchain (2-5 min, one-time)
python3 tools/get_deps.py [FAMILY|-b BOARD]        # fetch deps into lib/, hw/mcu/ (<1 s)
. $HOME/code/esp-idf/export.sh                     # Espressif only: before any build/flash/monitor

Build

Single example (CMake+Ninja, recommended, 1-3 s):

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

All examples for a board (15-20 s; some objcopy failures are non-critical). The build dir must be cmake-build-<board> — HIL tests expect that exact name:

cd examples
cmake -B cmake-build-raspberry_pi_pico -DBOARD=raspberry_pi_pico -G Ninja -DCMAKE_BUILD_TYPE=MinSizeRel . && cmake --build cmake-build-raspberry_pi_pico
  • Make: cd examples/device/cdc_msc && make BOARD=raspberry_pi_pico all
  • Espressif (ESP-IDF examples only, e.g. cdc_msc_freertos): after export.sh, cd examples/device/cdc_msc_freertos && idf.py -DBOARD=espressif_s3_devkitc build
  • Options (CMake -D… / Make …=…): CMAKE_BUILD_TYPE=Debug/DEBUG=1; LOG=2 (LOGGER=rtt for RTT); RHPORT_DEVICE=1; RHPORT_DEVICE_SPEED=OPT_MODE_FULL_SPEED

Flash

ninja cdc_msc-jlink       # CMake; Make: make BOARD=<board> flash-jlink
ninja cdc_msc-openocd     # CMake; Make: make BOARD=<board> flash-openocd
ninja cdc_msc-uf2         # CMake; Make: make BOARD=<board> all uf2
ninja -t targets          # list CMake targets

Espressif (after export.sh): idf.py -DBOARD=<board> flash / … monitor.

GDB Debugging

Look up JLINK_DEVICE / OPENOCD_OPTION in hw/bsp/*/boards/*/board.cmake (CMake) or board.mk (Make).

Terminal 1 — start a gdbserver:

JLinkGDBServer -device stm32h743xi -if SWD -speed 4000 -port 2331 -nogui   # JLink → :2331
openocd -f interface/stlink.cfg -f target/stm32h7x.cfg                     # OpenOCD → :3333
openocd -f interface/cmsis-dap.cfg -f target/rp2040.cfg -c "adapter speed 5000"   # rp2040/rp2350

Terminal 2 — connect (<port>: 2331 JLink, 3333 OpenOCD):

arm-none-eabi-gdb build/your_app.elf
(gdb) target remote :<port>    # then: monitor reset halt → load → continue

RTT: build LOG=2 LOGGER=rtt, run JLinkGDBServer with -RTTTelnetPort 19021, then JLinkRTTClient (timeout 20s JLinkRTTClient > rtt.log for non-interactive capture).

Testing

Unit (Ceedling, Unity+CMock, ~4 s):

sudo gem install ceedling
cd test/unit-test && ceedling test:all        # or ceedling test:test_fifo

HIL (2-5 min): invoke the hil skill (.claude/skills/hil/SKILL.md) — local vs remote mode, config selection, SSH copy steps, debugging. Requires pre-built examples (Build → “All examples for a board”).

Documentation

Sphinx docs in docs/ (.rst, or .md via MyST). Use the build-doc skill (.claude/skills/build-doc/SKILL.md) to build/preview locally and regenerate auto-generated files (tools/gen_doc.py + tools/gen_presets.py) after adding a board or dependency.

Code Size Metrics

Verify size impact before committing with the code-size skill (.claude/skills/code-size/SKILL.md) — it wraps tools/metrics_compare_base.py for the base-vs-branch worktree + build + compare. Scopes: single example (-e device/cdc_msc -b <board>, add --bloaty), all examples on a board (-b <board>), or all arm-gcc CI families (--ci). Reports land in cmake-metrics/<board>/metrics_compare.md (and _combined/ for --ci).

Static Analysis (PVS-Studio)

Use the pvs skill (.claude/skills/pvs/SKILL.md) — it builds the examples with an exported compile_commands.json and runs SAST + MISRA C:2023/C++:2008 for a board, emitting readable + SARIF output (~10-30 s). The examples build exports compile_commands.json by default.

Validation After Changes

  1. pre-commit run --all-files — format, spell, unit tests (10-15 s).
  2. Build at least one board's full example set (Build → “All examples for a board”) for modules you touched.
  3. Run relevant unit tests; add fuzz/HIL coverage for parsers or protocol state machines.

Boards good for local testing:

  • stm32f407disco — no external SDK
  • raspberry_pi_pico — Pico SDK required
  • Others: see hw/bsp/FAMILY/boards/

Device examples need real hardware to validate runtime behavior; must at least build.

Release

Cutting a release — version bump, regenerated files, the per-release changelog, validation, and the maintainer's commit/tag/GitHub-release — is handled by the make-release skill (.claude/skills/make-release/SKILL.md).

References

  • MCU reference manuals, datasheets, schematics: before answering register/bitfield/pinout/errata/timing questions from memory or the web — or changing a specific dcd/hcd driver — use the read-doc skill (.claude/skills/read-doc/SKILL.md) to cross-check against docs in $HOME/Documents/calibre-library; tell the user if the needed document is missing (skill no-ops if the library is absent).
  • Supported MCUs/boards: hw/bsp/ and docs/reference/boards.rst.
  • USB classes: src/class/{cdc,hid,msc,audio,…}/ — each has *_device.c and *_host.c.
  • Key files: src/tusb.h, src/tusb_config.h, tools/get_deps.py, tools/build.py, test/unit-test/project.yml.

Common Build Issues

  • Missing compiler → install gcc-arm-none-eabi.
  • Missing deps → python3 tools/get_deps.py FAMILY.
  • Unknown board → check hw/bsp/FAMILY/boards/.
  • objcopy errors in full builds are often non-critical; retry the single example.