4b1c8d16f7
Documentation tooling:
- Add the `build-doc` skill and `tools/build_doc.py` wrapper for local
Sphinx builds (clean / -W / open).
- Enable Markdown (MyST) in conf.py and auto-collect
examples/{device,host,dual}/*/README.md into a 3-level Examples nav
(Examples > Device/Host/Dual > example), noting each page's source
location and normalizing headings to a single H1.
- Remove the stale `.claude/commands/build-doc.md`; point the AGENTS.md
Documentation section at the skill.
Example docs:
- Add a README.md for every device/host/dual example: what it does, USB
interface table, notable tusb_config.h settings, generic CMake + Make
build steps, and how to try it.
- Fold each *_freertos variant into its base README, noting the FreeRTOS
source path and any RTOS-specific behavior.
Generated docs/examples/ output is git-ignored. Builds clean with
`sphinx-build -W`.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
CDC + UAC2
This example provides a composite CDC + UAC2 device.
Use Cases
-
The CDC + UAC2 composite device happens to be important, especially in the amateur radio community.
Modern radios (
rigs) like Icom IC-7300 + IC-705 expose a sound card and a serial device (composite device) to the computer over a single USB cable. This allows for Audio I/O and CAT control over a single USB cable which is very convenient.By including and maintaining this example in TinyUSB repository, we enable the amateur radio community to build (
homebrew) radios with similar functionality as the (expensive) commercial rigs. -
https://digirig.net/digirig-mobile-rev-1-9/ is a digital interface for interfacing radios (that lack an inbuilt digital interface) with computers. Digirig Mobile works brilliantly (is OSS!) and is a big improvement over traditional digital interfaces (like the SignaLink USB Interface). By using a CDC + UAC2 composite device, we can simplify the Digirig Mobile schematic, drastically reduce the manufacturing cost, and (again) enable the homebrewers community to homebrew a modern digital interface with ease themselves.
Build Steps
mkdir build && cd build
cmake -DBOARD=raspberry_pi_pico ..
cmake --build .
Make:
make BOARD=raspberry_pi_pico all
USB Descriptors
| Interface | Class driver |
|---|---|
| 0–2 | UAC2 audio (control, speaker streaming, mic streaming) |
| 3–4 | CDC (virtual serial) |
Configuration
Notable tusb_config.h settings:
#define CFG_TUD_CDC 1
#define CFG_TUD_AUDIO 1
#define CFG_TUD_AUDIO_FUNC_1_N_FORMATS 2 // two audio formats
#define CFG_TUD_AUDIO_FUNC_1_MAX_SAMPLE_RATE 96000 // 48000 on Renesas RX
#define CFG_TUD_CDC_RX_BUFSIZE (TUD_OPT_HIGH_SPEED ? 512 : 64)
#define CFG_TUD_CDC_TX_BUFSIZE (TUD_OPT_HIGH_SPEED ? 512 : 64)
How to use
After flashing, the device enumerates as both a USB sound card and a serial port:
- Audio: appears as a standard UAC2 sound card — list it with
arecord -l/aplay -lon Linux, or find it in the OS sound settings. Audio is sourced/sunk by the example'saudio_task. - Serial: the CDC port shows up as
/dev/ttyACMx(Linux/macOS) or a COM port (Windows); open it with any terminal.
In the amateur-radio setup, digital-mode software (WSJT-X, fldigi, …) uses the sound card for audio and the serial port for CAT/PTT control — both over the one cable.