Multiport adapter on RPi2040

[LsrSal]

I am trying to make multi-port USB MIDI adapter with RPi2040 (the tiny "zero" version, that I successfully used to create USB_MIDI_host for my FP10). Single MIDI port works great, even SysEx appeared to be working (not too much testing yet though). But multi-port somehow I cannot get under control.

Interface Initialization

1. initialization of USB MIDI single port device:
   USBMIDI_Interface USB_midi;
   Works as expected.

2. Initialize two interfaces, reference example that doesn't create two interfaces (not on RPi2040 with tinyUSB stack):
   USBMIDI_Interface USB_midi_1; USBMIDI_Interface USB_midi_2;
   Only one interface is created.

3. Other way to init it that does create extra interfaces on the same USB:
   USBMIDI_Interface USB_midi(2);
   Interesting to note that I was able to create no more than 3 interfaces. Tyring to make 4 => nothing is created. But 3 is plenty for me.

In bullet 3. I was not able to route specifically to any of 2 or 3 interfaces. only first one transmits and all receiving the same thing. I was tyring to index interface's ID with squate brackets, round brackets and no brackets at all - I was not able to call specific USB MIDI interface other than first one by "USB_midi".

• Is bullet 3 a correct way to init multi-port USB MIDI?
• If it is - how can I call each ports to route between them? Port's IDs?
• Or maybe it is a USB stack limitation? I use Adafruit tinyUSB stack, the only one I was able to compile it with. And it is working fine with single port.
• Can I create transmit_only port?
• Can I use soft serial transmit only port to use for MIDI out? Ultimately I would like to make a replacement for my MT4 2x4 that is no longer supported in Windows-x64.

Thanks for any help!

[tttapa]

Arguments to the USBMIDI_Interface constructor are forwarded to the target-specific backend. In your case, that would be the Adafruit_USBD_MIDI class: https://github.com/adafruit/Adafruit_TinyUSB_Arduino/blob/master/src/arduino/midi/Adafruit_USBD_MIDI.h
The number of cables supported by TinyUSB may be limited, but I have never looked at it in detail. Control Surface should support all 16 cables.

You can only have a single instance of the USBMIDI_Interface class in your program (bullet 3 is the correct approach). Different virtual cables map to different cable numbers in the MIDI messages. To route messages originating from different cables to different serial MIDI interfaces, use the MIDI_Pipe class as shown here: https://forum.arduino.cc/t/control_surface-h-usage-on-teensy-4-1/691064/183?u=pieterp

AFAIK, most USB libraries will always allocate endpoints in both directions for MIDI, so a transmit-only port is not possible.

SoftwareSerial is supported, but not recommended. HardwareSerial or PIO-based serial are preferable.

[LsrSal]

Pieter,

Thank you very much for your explanation! That clears a few things but I am still stuck.

After some searching I understand that multiple MIDI ports, a.k.a. virtual cables, utilizing additional (usually 4th) prefix byte in USB sentence to specify messages association with specific "Cable".
I am still not able to create functional code to "CableFilterMIDI_Pipe" for RPi2040 (zero).
Tried to use CoPilot to solve it but no proposed code can be compiled, and it requesting bouncing constantly between MBED and Earle Philhower cores, complaining during compilation that I need to use another core because this one is missing something (pipes filtering, variable types, multiple Cables [even though it compiles and runs and apparently does have multiple cables]).

I guess instead of using pipes with filters, it is possible to write very low level code to read, parse and forward raw USB sentences, but Pipes looks so much cleaner, and as I understand, that data has much faster path, so it is preferred to use pipes, with filters. But I still cannot wrap my head over pipes and filters. Apparently neither is CoPilot.

Could you please, if possible, to provide an example of 2x2 USB midi adapter code with 2 virtual Cables (MIDI ports on single USB) to be associated separately with each of two available hardware serial ports? Is it possible at all for RPi2040?

Really appreciate your help!