Workshop System Computer - USB Audio & MIDI Firmware

This firmware turns the Workshop System Computer into a class-compliant USB Composite Device providing:

• 6-Channel USB Audio Interface (Input & Output)
• USB MIDI Interface
• CV/Gate Integration via Hardware I/O

Features

Mode 1: Normal (Switch Middle)

• 6-Channel Audio I/O: Direct mapping of the 6 hardware channels to USB Audio channels 1-6.

Mode 2: Alt Mode (Switch Up)

• Audio L/R: Stereo Passthrough on USB Channels 5/6.
• CV 1: 1V/Oct Pitch Interface (MIDI Note <-> CV).
• CV 2: CC Interface (MIDI CC <-> CV).
• Pulse 1: Gate Interface (Note On/Off <-> Pulse).
• Pulse 2: Clock/Run Interface.

Mode 3: Audio Only (Switch Down)

• Turns off all Midi functionality, leaving only the configured USB Audio channels.

Configuration & Defaults

The firmware ships with the following Default Settings (customizable via the Web Interface):

• Sample Rate: 44.1 kHz
• Channel Count: 4 Channels (Audio 1/2 + CV 1/2) enabled for both Input and Output.
• Input Mapping:
  • Audio 1/2: Audio Stream
  • CV 1: Pitch (Ch 1)
  • CV 2: CC 4 (Ch 1)
  • Pulse 1: Gate (for CV 1)
• Output Mapping:
  • Audio 1/2: Audio Stream
  • CV 1: Pitch (Ch 1)
  • CV 2: CC 4 (Ch 1)
  • Pulse 1: Gate
  • Pulse 2: Clock
• Knobs:
  • Main: CC 1 (Ch 1)
  • X: CC 2 (Ch 1)
  • Y: CC 3 (Ch 1)

Web Interface: All settings (Sample Rate, Channel Count, CV/Pulse Modes) can be adjusted using the Workshop System Web Tools. The configuration can be saved to the device's flash memory.

[!WARNING] USB 1.1 Bandwidth & Stability

This device operates as a Full Speed USB 1.1 device. Bandwidth is extremely limited, especially when combined with MIDI traffic. Performance varies significantly by Operating System and Host Controller.

Tested Configurations (Testing Required):

• macOS: 6 Channels @ 48 kHz .
• Windows: Limited bandwidth. Usually requires reducing to 6 Channels @ 24 kHz or 4 Channels @ 44.1 kHz.
• Linux: 2 channel audio works up to 48kHz. 4 channel audio works up to 24kHz

Please test different configurations/ Audio Drivers for stability on your specific system.

• Raspberry Pi Pico SDK
• CMake > 3.13

[!IMPORTANT] You MUST update the TinyUSB library within your Pico SDK to the latest version.
The default version included with older SDK releases may contain bugs affecting Audio Class devices.

To update:

cd $PICO_SDK_PATH/lib/tinyusb
git checkout master
git pull

Setup & Building

1. Configure Environment: Run the provided helper script to add SDK paths to your shell configuration (Mac/Linux):

   ./configure_shell.sh
   source ~/.zshrc  # Or restart terminal
   

2. Build:

   mkdir build
   cd build
   cmake ..
   make
   

3. Flash: Hold the BOOTSEL button on your Pico/Computer board, plug it in, and copy the generated usb_bridge.uf2 to the drive.

Created for the Music Thing Modular Workshop System by Vincent Maurer (https://github.com/vincent-maurer/) with assistance from Google Gemini.

Thank you to everyone on the Workshop System Discord server, that helped testing and especially to Chris Johnson (https://github.com/chrisgjohnson) for the initial USB-Audio project, the ComputerCard library and the great support.