Project 4: USB Audio Class Driver (Bare Metal/Embedded)

A driver for a USB audio device (like a USB microphone or DAC) on a microcontroller or using libusb on Linux.

Quick Reference

Attribute Value
Primary Language See main guide
Alternative Languages N/A
Difficulty See main guide
Time Estimate See main guide
Knowledge Area See main guide
Tooling See main guide
Prerequisites C programming, USB basics, embedded experience helpful

What You Will Build

A driver for a USB audio device (like a USB microphone or DAC) on a microcontroller or using libusb on Linux.

Why It Matters

This project builds core skills that appear repeatedly in real-world systems and tooling.

Core Challenges

  • Parsing USB descriptors to find audio interfaces
  • Setting up isochronous endpoints for streaming
  • Understanding USB Audio Class (UAC) protocol
  • Handling clock synchronization between host and device

Key Concepts

  • Map the project to core concepts before you code.

Real-World Outcome

# Plug in a USB microphone or DAC
$ lsusb
Bus 001 Device 005: ID 0d8c:0014 C-Media Electronics, Inc. USB Audio Device

# Run your driver in user-space (using libusb)
$ sudo ./usb_audio_driver

╔═══════════════════════════════════════════════════════════════════╗
║              USB Audio Class Driver v1.0                           ║
╠═══════════════════════════════════════════════════════════════════╣
║ Scanning for USB Audio devices...                                 ║
╚═══════════════════════════════════════════════════════════════════╝

Found USB Audio Device:
  Vendor ID: 0x0d8c
  Product ID: 0x0014
  Manufacturer: C-Media Electronics
  Product: USB Audio Device

Parsing descriptors...
  Interface 0: Audio Control (bInterfaceClass=1, bInterfaceSubClass=1)
  Interface 1: Audio Streaming (bInterfaceClass=1, bInterfaceSubClass=2)
    - Endpoint: 0x84 (IN, Isochronous)
    - Sample rates: 48000 Hz, 44100 Hz
    - Format: PCM 16-bit
    - Channels: 2 (Stereo)

Claiming interface 1...
Configuring for 48000 Hz, 16-bit, Stereo...

Starting audio capture:
[INFO] Isochronous transfer scheduled (1024 bytes/packet, 8 packets)
[INFO] Received 1024 bytes (512 frames)
[INFO] Received 1024 bytes (512 frames)
[INFO] Received 1024 bytes (512 frames)

Captured 30 seconds of audio → output.raw

Implementation Guide

  1. Reproduce the simplest happy-path scenario.
  2. Build the smallest working version of the core feature.
  3. Add input validation and error handling.
  4. Add instrumentation/logging to confirm behavior.
  5. Refactor into clean modules with tests.

Milestones

  • Milestone 1: Minimal working program that runs end-to-end.
  • Milestone 2: Correct outputs for typical inputs.
  • Milestone 3: Robust handling of edge cases.
  • Milestone 4: Clean structure and documented usage.

Validation Checklist

  • Output matches the real-world outcome example
  • Handles invalid inputs safely
  • Provides clear errors and exit codes
  • Repeatable results across runs

References

  • Main guide: AUDIO_SOUND_DEVICES_OS_LEARNING_PROJECTS.md
  • Primary references are listed in the main guide