ScummVM hangs/crashes on game start with real MT-32 over USB MIDI

[bleggett]

I've built an MT-32 Pi (uses Munt internally, but presents as a normal MIDI device) ​https://github.com/dwhinham/mt32-pi - which I'm connecting to my PC via a Roland UM-ONE Mk 2 USB MIDI interface.

This combo works perfectly for both Dosbox and Exult - they see it as an external real MT-32, and everything (from CM-32 sounds to Sysex) works just fine.

However, ScummVM (daily build as of this issue creation date) crashes on startup if I tell it to use this device as a "real" MT-32. It will send MIDI to the device just fine as a generic GM MIDI device, but it will hang on every game if I try to use MT-32 mode specifically.

I get no console errors - just a hang on engine load. Disabling MT-32 mode in ScummVM and sending normal GM to the device works and stops the hang (but naturally produces incorrect sounds for MT-32 games, as the device is being sent GM data).

Again - only ScummVM has this problem, so I think this is an issue with ScummVM and external "real" MT-32s over USB specifically.