feat(audio): add USB Audio Host (UAC 1.0) support

Add TinyUSB Host Audio class driver supporting UAC 1.0 devices.

Features:
- Support multiple Audio Streaming (AS) interfaces with independent format storage
- Support both IN (Microphone) and OUT (Speaker) endpoints
- Per-AS interface format info: channels, sample rate, bit resolution
- Support Feature Unit volume control
- Support sampling frequency get/set
- Add host/audio_host example for STM32F407 discovery board
- Support mono-to-stereo conversion for loopback

Changes:
- Add src/class/audio/audio_host.c and audio_host.h
- Register AUDIO driver in usbh.c
- Add CFG_TUH_AUDIO macro in tusb_option.h
- Add host/audio_host example with CMake and Makefile build support

Tested with Jabra USB headset (stereo speaker + mono microphone) on STM32F407 disco.

1 files changed, 98 insertions, 0 deletions

diff --git a/examples/host/audio_host/README.md b/examples/host/audio_host/README.md
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+# USB Audio Host Example
+
+This example demonstrates how to use TinyUSB's USB Audio Host driver (TUH_AUDIO) to communicate with a UAC 1.0 compatible USB Audio Device.
+
+## Features
+
+- Enumerates and mounts USB Audio Class 1.0 devices
+- Receives audio data from IN endpoint (e.g., microphone)
+- Sends audio data to OUT endpoint (e.g., speaker)
+- Sets sampling frequency via control requests
+- Demonstrates isochronous transfer handling
+
+## Supported Devices
+
+This example supports any UAC 1.0 compliant USB Audio device, such as:
+- USB microphones
+- USB speakers/headphones
+- USB audio interfaces
+
+## Building
+
+### Using CMake (recommended)
+
+```bash
+cd examples/host/audio_host
+mkdir -p build && cd build
+cmake -DBOARD=<your_board> -G Ninja ..
+cmake --build .
+```
+
+Replace `<your_board>` with your target board name (e.g., `raspberry_pi_pico`, `stm32f407disco`, etc.)
+
+### Using Make
+
+```bash
+cd examples/host/audio_host
+make BOARD=<your_board> all
+```
+
+## Flashing
+
+```bash
+# Using CMake
+ninja flash
+
+# Using Make
+make BOARD=<your_board> flash
+```
+
+## Usage
+
+1. Build and flash the example to your board
+2. Connect a USB Audio device (UAC 1.0) to the USB host port
+3. Open a serial terminal to view output
+4. The example will:
+   - Print device information when mounted
+   - Set sampling frequency to 48kHz
+   - Receive audio samples from the device (IN endpoint)
+   - Send test sine wave audio to the device (OUT endpoint)
+
+## Serial Output Example
+
+```
+TinyUSB Host USB Audio Example
+Connect a USB Audio Device (UAC 1.0) to test
+Audio device mounted: idx=0, daddr=1
+  --- Microphone ---
+    IN EP: 0x81 (max size: 192)
+    Input Terminal: ID=1, Type=0x0201, Channels=1
+    Format Type: 1, Channels: 1, SubFrameSize: 2, BitResolution: 16
+    Sampling Freq: Discrete, count=4
+      Freq[0]: 44100 Hz
+      Freq[1]: 48000 Hz
+      Freq[2]: 96000 Hz
+      Freq[3]: 192000 Hz
+  --- Speaker ---
+    OUT EP: 0x02 (max size: 192)
+    Output Terminal: ID=2, Type=0x0301
+    Format Type: 1, Channels: 2, SubFrameSize: 2, BitResolution: 16
+    Sampling Freq: Continuous range 8000 Hz - 48000 Hz
+  Feature Unit: ID=3, SourceID=1
+  Setting IN sampling frequency to 48000 Hz
+  Setting OUT sampling frequency to 48000 Hz
+  Sampling frequency set OK, ready for isochronous transfer
+```
+
+## Configuration
+
+Edit `src/tusb_config.h` to modify:
+- `CFG_TUH_AUDIO_MAX`: Maximum number of audio devices supported
+- `CFG_TUH_AUDIO_EPIN_BUFSIZE`: IN endpoint buffer size
+- `CFG_TUH_AUDIO_EPOUT_BUFSIZE`: OUT endpoint buffer size
+
+## Notes
+
+- This example uses isochronous transfers which require precise timing
+- For production applications, synchronize audio transfers with the device's audio clock
+- The example sends a simple sine wave for testing; replace with actual audio data in real applications