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# 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
```bash
mkdir build && cd build
cmake -DBOARD=raspberry_pi_pico ..
cmake --build .
```
Make:
```bash
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:
```c
#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 -l` on Linux, or find it in the OS sound settings. Audio is sourced/sunk by the example's `audio_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.
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