In it’s current state I’m unable to actually use the library to list midi ports, so there’s still more sleuthing to be done here.
thejohncotton
octetta
If you got the ALSA seq utilities with your build, see if you can run cmd "aconnect -l” to list the devices.
0
mclarenlabs
McLaren Labs here - mentioned earlier in the thread.
You might find our ObjC project interesting in showing how to interface with ALSA “sequencer” interface (MIDI) and PCM interface (audio)
some example tools here
ALSA is very powerful, but it has a decent learning curve. Our little examples might help 
-Tom
2
thejohncotton
Here’s the link to my system: GitHub - thejohncotton/nerves_system_rpi4: Base Nerves system configuration for the Raspberry Pi 4 · GitHub
I’m able to run aconnect now, and get back
client 0: 'System' [type=kernel]
0 'Timer '
1 'Announce '
I think I’m on the right track, but not able to get any midi devices to show up yet. I’ve got several to try most are class compliant usb devices so shouldn’t need drivers.
1
thejohncotton
The latest commit to my system will recognize usb midi devices. I can’t post a screenshot here but the happy command return is:
iex(1)> cmd "aconnect -i"
client 0: 'System' [type=kernel]
0 'Timer '
1 'Announce '
client 20: 'Virtual Raw MIDI 1-0' [type=kernel,card=1]
0 'VirMIDI 1-0 '
client 21: 'Virtual Raw MIDI 1-1' [type=kernel,card=1]
0 'VirMIDI 1-1 '
client 22: 'Virtual Raw MIDI 1-2' [type=kernel,card=1]
0 'VirMIDI 1-2 '
client 23: 'Virtual Raw MIDI 1-3' [type=kernel,card=1]
0 'VirMIDI 1-3 '
client 24: 'CH345' [type=kernel,card=2]
0 'CH345 MIDI 1 '
client 28: 'OP-Z' [type=kernel,card=3]
0 'OP-Z MIDI 1 '
0
2