USB Midi Device - MTC via SysEX functionality #18450

mungewell · 2025-11-21T01:07:40Z

mungewell
Nov 21, 2025

I see that USB Midi has been added (yeah!!), and a simple example suggested:
https://github.com/micropython/micropython-lib/blob/master/micropython/usb/examples/device/midi_example.py

and that runs OK on my RP2040 and see the output on my laptop...

$ amidi -l
Dir Device    Name
IO  hw:2,0,0  Board in FS mode MIDI 1

$ amidi -p "hw:2,0,0" -t 10 -r temp.bin  ; hexdump -C temp.bin
^C
75 bytes read
00000000  80 3c 40 b0 40 00 90 3c  40 90 3c 40 80 3c 40 b0  |.<@.@..<@.<@.<@.|
00000010  40 06 90 3c 40 80 3c 40  b0 40 07 90 3c 40 80 3c  |@..<@.<@.@..<@.<|
00000020  40 b0 40 08 90 3c 40 80  3c 40 b0 40 09 90 3c 40  |@.@..<@.<@.@..<@|
00000030  80 3c 40 b0 40 0a 90 3c  40 80 3c 40 b0 40 0b 90  |.<@.@..<@.<@.@..|
00000040  3c 40 80 3c 40 b0 40 0c  90 3c 40                 |<@.<@.@..<@|
0000004b

I would like to send Midi MTC (effectively SysEX packets), but there does not appear to be functions for SysEx in:
https://github.com/micropython/micropython-lib/blob/master/micropython/usb/usb-device-midi/usb/device/midi.py#L27

I wrote a test script, but am a bit lost on how to send the packet of data that I have assembled.
mtc_example.py.zip

    def send_long_mtc(self):
        print("Full: 0x%8.8x" % self.raw)

        packet = bytearray(b"\xF0\x7F\x7F\x01\x01")
        packet.append(((self.raw & 0x1F000000) > 24) + (0b11 < 5))  # hour + '30fps'
        packet.append(( self.raw & 0x003F0000) > 16)            # minutes
        packet.append(( self.raw & 0x00003F00) > 8)             # seconds
        packet.append(  self.raw & 0x0000003F)                  # frames
        packet.append(0xF7)

        # send packet to host, length 7 bytes???
        #self.send_sysex(packet)

Anyone got suggestions?

mungewell · 2025-11-21T02:28:16Z

mungewell
Nov 21, 2025
Author

I found the table 4.2 mentioned in the code, and that suggests I have to fragment the packet. The send_quarter_mtc only sends 2 bytes which should be possible....

I coded as follows, but still no joy.

    def send_quarter_mtc(self):
        #print("Quarter 0x%8.8x 0x%8.8x" % (self.raw, self.count))

        w = self._tx.pend_write()
        if len(w) < 4:
            return False  # TX buffer is full. TODO: block here?

        # assemble packet
        w[0] = _CIN_SYSEX_END_2BYTE     # 0x6
        w[1] = 0xF1

        # figure the right packet to send
        if not self.count & 0x4:
            if not self.count & 0x2:
                if not self.count & 0x1:
                    w[2] = (self.raw & 0x0000000F)
                else:
                    w[2] = (((self.raw & 0x000000F0) > 4) + 0x10)
            else:
                if not self.count & 0x1:
                    w[2] = (((self.raw & 0x00000F00) > 8) + 0x20)
                else:
                    w[2] = (((self.raw & 0x0000F000) > 12) + 0x30)
        else:
            if not self.count & 0x2:
                if not self.count & 0x1:
                    w[2] = (((self.raw & 0x000F0000) > 16) + 0x40)
                else:
                    w[2] = (((self.raw & 0x00F00000) > 20) + 0x50)
            else:
                if not self.count & 0x1:
                    w[2] = (((self.raw & 0x0F000000) > 24) + 0x60)
                else:
                    w[2] = (((self.raw & 0x10000000) > 28) + 0x70 + 0b0110)

        # finish assembling and send
        w[3] = 0
        self._tx.finish_write(4)
        self._tx_xfer()

0 replies

mungewell · 2025-11-21T03:09:59Z

mungewell
Nov 21, 2025
Author

Got it!

As I was loosing the console, I didn't get error message that this was (I guess) undefined. Setting the value to 0x6 works...

w[0] = _CIN_SYSEX_END_2BYTE

But I don't know if I am doing the correct way of breaking up the longer packet. Seems wrong to use something called 'END' in the middle of the packet.
mtc_example.py.zip

0 replies

mungewell · 2025-11-22T01:26:35Z

mungewell
Nov 22, 2025
Author

More tweaking to fix bugs and clean up code and we have:
mtc_example.py.txt

Here it is controlling 'xjadeo'. Script starts at '00:00:00:00' counts for 2mins, then resets to the start, and runs again.

1 reply

mungewell Nov 23, 2025
Author

And now the demo video :-)

https://www.youtube.com/watch?v=kkTFQ0azi5w

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