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microbook-linux

A Linux kernel ALSA driver for the MOTU MicroBook mk1 USB audio interface (07fd:0004). This is a custom (non-UAC) device: mainline snd-usb-audio has a quirk for the MicroBook II that matches the same USB ID, but it cannot drive the mk1. This module implements the vendor control protocol and isochronous audio transport directly.

Features

  • Playback: 2-channel, 24-bit packed (S24_3LE), 44.1 and 48 kHz
  • Capture: 4-channel, 24-bit packed (S24_3LE), 44.1 and 48 kHz
  • Mixer controls: Headphone / Line / PCM volumes, mic trim, phantom power, pad, guitar trim — via ALSA mixer (alsamixer, amixer)
  • Hardware direct monitoring: per-input zero-latency monitor levels (Guitar / Mic / Line Monitor Volume), decoded from the device's DSP mixer matrix
  • Low latency: ~15 ms round trip at 48 kHz out of the box, tunable to under 10 ms; sample rate is locked while both directions are open so a rate change cannot reboot the device under a running stream
  • PipeWire/Cinnamon integration: split stereo sources, batch-aware timing, and persistent rate/quantum configuration
  • Half-duplex guard: prevents crackling through USB hub transaction translators; allow_duplex=1 for direct USB connections
  • debugfs register probe: raw access to the device's DSP address space for further reverse engineering

Repository layout

driver/          kernel module (motu-microbook.ko)
re/              reverse engineering notes and register maps
contrib/         WirePlumber/PipeWire/modprobe configuration
tools/           motu-probe.sh — DSP register probe (needs the driver's debugfs)
COPYING          GPL-2.0 license

Quick start

cd driver && make
sudo insmod motu-microbook.ko allow_duplex=1
speaker-test -D plughw:CARD=MOTU -c 2 -r 48000 -f 440 -t sine -p 5
alsamixer -c MOTU

allow_duplex=1 is right for a direct USB port; leave it off through a hub. For a permanent setup — module options, desktop integration and low-latency configuration that survive a reboot — see contrib/README.md.

See driver/README.md for full build/load/test instructions and the latency model, and re/ANALYSIS.md plus re/cuemix_registers.md for the reverse engineering work.

License

GPL-2.0-only. See COPYING.