On this fork:

some updates specific to my use case running on raspberry pi zero w:

• generate multiple clocks with various dividers to make longer, "lower-resolution" step sequences on devices with very limited step count (e.g. volca bass)
• crude autostart and auto-restart of mirg when OP-1 is connected as USB host
• initial implementation at a visualizer using pimomori scroll phat hd, running in separate process and controlled by IPC via unix sockets - works more or less, but I stopped pursuing this further

mirg

a simple program for the raspberry pi. Listens to MIDI clock/start/stop on a USB port, provides korg-style pulse sync on GPIO. For example, this lets you sync Korg Volca or Teeange Engineering OP-XX to any device which provides clock via USB, such as Elektron Analog series or Teenage Engineering OP-1.

Dependencies

libasound2-dev is needed for USB-MIDI:

sudo apt-get install libasound2-dev

this bcm2835 library is needed to use the GPIO pins: http://www.airspayce.com/mikem/bcm2835/index.html

Follow the instructions on that site for installation.

Compile mirg

gcc -o mirg mirg.c -lbcm2835 -lasound

Usage

Connect the USB-MIDI device you want to use as master clock before starting mirg. Find out the ALSA ID of your MIDI device using amidi:

amidi -l

This will list all connected devices. Use your chosen device, e.g. hw:1,0,0 as an argument to mirg:

./mirg hw:1,0,0

Make sure your MIDI device sends clock/start/stop via USB. Press play on your MIDI device. Mirg creates a Korg-style pulse every 8th-note (once every 12 MIDI clock ticks) on GPIO pin 17. You'll need to connect a minijack cable to that pin, e.g. use a standard modular patch cable and cut off one end. Connect tip to pin 17, connect sleeve to ground.