It it possible to name separate USB MIDI interfaces?

[HLammers]

It is fairly easy to implement multiple midi interfaces over one USB connection, but how do I give each one a unique name?

To demonstrate what I’m talking about, let‘s modify midi_example.py, by changing lines 45 to 47:

m = MIDIExample()
# Remove builtin_driver=True if you don't want the MicroPython serial REPL available.
usb.device.get().init(m, builtin_driver=True)

into:

m = MIDIExample()
n = MIDIExample()
o = MIDIExample()
# Remove builtin_driver=True if you don't want the MicroPython serial REPL available.
usb_device_core.get().init(m, n, o, builtin_driver=True, product_str="Test")

After this change three MIDI connections show up in my DAW (FL Studio 2024): ‘Test’, ‘Test #2’ and ‘Test #3’. I assume they acually are all three called ‘Test’ (i.e. the product string value) and ‘#2’ and ‘#3’ are added by the DAW itself. Is there any way to give each Interface instance a unique name, via product string or otherwise?

Edit
Perhaps multiple virutal cables is a better approach to achieve this, but that hasn’t been implemented in usb.device.midi. Does anyone know how to implement that?

[projectgus]

Is there any way to give each Interface instance a unique name, via product string or otherwise?

Not from the USB side, I don't think. There's no string field in any of the MIDI descriptors, just the device product string. You might be able to change the names in the host computer OS, or in Windows maybe even via a custom .inf driver file, but I'm guessing that won't solve the problem for you.

Perhaps multiple virutal cables is a better approach to achieve this, but that hasn’t been implemented in usb.device.midi. Does anyone know how to implement that?

This is probably the way, although I think these also won't provide you with different names just different numbered "Jack IDs".

As per the comment here, the driver has all of the structure to add multiple "jacks" in one descriptor but I didn't have a lot of luck getting something useful out of it.

[projectgus]

Not from the USB side, I don't think. There's no string field in any of the MIDI descriptors

Oh actually I am wrong, there is an interface string descriptor index (iInteface) that's currently not passed through by the driver in this call:
https://github.com/micropython/micropython-lib/blob/master/micropython/usb/usb-device-midi/usb/device/midi.py#L174

You could try patching the desc_cfg() function in midi.py to something like:

    def desc_cfg(self, desc, itf_num, ep_num, strs):
        # Start by registering a USB Audio Control interface, that is required to point to the
        # actual MIDI interface
        desc.interface(itf_num, 0, _INTERFACE_CLASS_AUDIO, _INTERFACE_SUBCLASS_AUDIO_CONTROL, iInterface=len(strs))
        strs.append("interface string")

If this works then we could add an optional interface_name argument to the MIDIInterface class, that passes through here.

[dhalbert]

A couple of caveats here that have been confusing to CircuitPython users, where we have a MIDI renaming capability:

1. The device and jack names on macOS are very sticky. They get cached the first time the device is seen, and subsequent changes are ignored. You have to delete the device to get new names to show up. This caching may also be true on Windows.
2. On Windows, either the interface name or the jack names are not very visible (I forget which), and don't show up in Device Manager.

[projectgus]

Thanks for the heads up, @dhalbert. If there is a jack name capability in USB MIDI then my first reply is wrong on two counts! Apologies, @HLammers. I'll try and dig into this more when I have some time.

[dhalbert]

See https://docs.circuitpython.org/en/latest/shared-bindings/usb_midi/index.html#usb_midi.set_names. Also, we recently found this gotcha on Windows, that jack names longer than 31 chars break something, even though that's not inherently a USB length restriction that we know of: adafruit#9871

[HLammers]

Thanks @projectgus and @dhalbert!

I tried patching the desc_cfg() function in midi.py to:

        # Start by registering a USB Audio Control interface, that is required to point to the
        # actual MIDI interface
        global interface_count
        interface_count += 1
        desc.interface(itf_num, 0, _INTERFACE_CLASS_AUDIO, _INTERFACE_SUBCLASS_AUDIO_CONTROL, iInterface=len(strs))
        strs.append(f'interface {interface_count}')

But now it creates three MIDI ports, each called ‘Interface 6’, while it should be ‘Interface 4’, ‘Interface 5’ and ‘Interface 6’ (numbers 1 to 3 are taken by the dummy calls to desc_cfg).

I do not have time now to do more testing to try to figure out why it refers each time to the last string. I guess the clue to that must be in core.pi. The annoying thing is that I’m using VS Code (on Windows 11), with the MicroPico extension, which doesn’t reconnect to the REPL after self.active(True) is called in _Device.init - which makes debugging very hard (I guess that’s an issue to raise in the MicroPico repository).