Ability to create more than 1 MIDI `PortIn` or `PortOut`

[probonopd]

Thanks for this library which allowed me to prototype a MIDI controller rapidly.

Some MIDI controllers expose more than one MIDI interface, and I need to recreate that using Adafruit_CircuitPython_MIDI on a Raspberry Pi Pico.

However,

circuitpython/shared-bindings/usb_midi/PortOut.c

Lines 21 to 24 in 79fd8b7

	//| """You cannot create an instance of `usb_midi.PortOut`.
	//|
	//| PortOut objects are constructed for every corresponding entry in the USB
	//| descriptor and added to the ``usb_midi.ports`` tuple."""

The same goes for usb_midi.PortIn.

It would be extremely useful if it was possible to create more than one MIDI interface per direction.

If that is not possible, then being able to choose the MIDI "cable number" would already be helpful.

References:

• My use case: Add DAW Controller support for various Arturia controllers probonopd/MiniDexed#743 (comment)
• Upstream issue: Multi MIDI Device with RP2040 hathach/tinyusb#1295
• Upstream solution in C: https://github.com/rppicomidi/midi-multistream2usbdev - maybe @jepler knows how to adopt this in CircuitPython?

[dhalbert]

The current MIDI descriptor we use is here: https://github.com/adafruit/circuitpython/blob/main/shared-module/usb_midi/__init__.c

To construct this dynamically would be a lot of code, and would not fit on some smaller boards that currently provide MIDI. An alternative would be to let the user supply their own descriptor, or some part of it. We allow that for custom HID devices.

If you could record and supply the fancier USB MIDI descriptor from an Arturia device, that would be helpful. Having said that, this is the first time we've gotten a request for fancier MIDI, so this would be a long-term project. We would welcome a generalized PR if anyone is interested in working on this.

[probonopd]

Thanks @dhalbert. All I am looking for is to have 2 MIDI PortIn and 2 PortOut instead of 1 each, on the Pi Pico.

Currently I have:

midi = adafruit_midi.MIDI(midi_in=usb_midi.ports[0], midi_out=usb_midi.ports[1], in_channel=0, out_channel=0, in_buf_size=512, debug=debugging_on)

I would like to add:

midi1 = adafruit_midi.MIDI(midi_in=usb_midi.ports[2], midi_out=usb_midi.ports[3], in_channel=0, out_channel=0, in_buf_size=512, debug=debugging_on)

In other words, I would like to also have usb_midi.ports[2] and midi_out=usb_midi.ports[3].

So are you saying that this would currently require rebuilding CircuitPython in C?

I don't have an Arturia device at hand.

[probonopd]

If that is not possible, then being able to choose the MIDI "cable number" would already be helpful.

Looks like all I'd need is a way, from Python, to change the 0 to 1 there, and I would be sending on cable 1 rather than cable 0:

circuitpython/shared-module/usb_midi/PortOut.c

Line 13 in 2d2fa28

return tud_midi_stream_write(0, data, len);

Unfortunately, there is currently no way to do that from Python, is there?
How much of an effort would it be to make this changeable from the Python side?

[dhalbert]

The current USB MIDI descriptor is fixed, and describes one MIDI device with two ports, one In and one Out. Do you want one device with four ports, two In and two Out? Or do you want two independent MIDI devices?

[probonopd]

I am looking for either

• One device with dour ports, two In and two Out (I assume this makes the second set of ports use MIDI cable 1 rather than 0), or (if this is easier)
• A way to send and receive on MIDI cable 1 rather than 0