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third_party/tinyusb/examples/device/cdc_uac2/README.md

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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.