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Bug #1066: Add helper function to send SysEx/MTC via usb-device-midi - #1068

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Bug #1066: Add helper function to send SysEx/MTC via usb-device-midi#1068
mungewell wants to merge 1 commit into
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@mungewell

@mungewell mungewell commented Nov 25, 2025

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I was using USB-device-midi to send MTC to the host, which is essentially SysEx. But was slowed by the missing helper function to send the packet of SysEx. Anyhow, I wrote one...

Full example script here:
https://github.com/orgs/micropython/discussions/18450#discussioncomment-15043069

@mungewell
usb-device-midi: Add helper function to send SysEx/MTC messages.
684f62c 
Signed-off-by: Simon Wood <simon@mungewell.org>
@dpgeorge dpgeorge linked an issue Dec 3, 2025 that may be closed by this pull request
USB-device-midi is missing helper function to send SysEx #1066
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@dpgeorge

dpgeorge commented Dec 3, 2025

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Thanks for the contribution.

But I'm a bit confused, I thought system exclusive messages were a completely different format, namely:

  • they start with 0xF0
  • they have an number of data bytes with the most-sig-bit clear
  • they end with 0xF7

How does that differ to the sys ex added here?

@mungewell

mungewell commented Dec 4, 2025

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You are correct, SysEx generally starts with 0xF0 and ends with 0xF7.

The helper function takes an array of bytes (say "0xf07f7f010160000000f7") and fragments it to pass over USB-midi protocol, then the USB host reassembles it to pass to client application.

The example script (for Pico) generates both the long and short messages that MTC uses.

dpgeorge
dpgeorge reviewed Jul 1, 2026
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Comment thread micropython/usb/usb-device-midi/usb/device/midi.py
def control_change(self, channel, controller, value):
self.send_event(_CIN_CONTROL_CHANGE, _MIDI_CONTROL_CHANGE | channel, controller, value)