MIDI MMC Messages & Writing Drivers

[stoermelder (Ben)]

Hi. I have some insights on this topic.
These MMC messages seem to be a special type of SysEx messages. Rack’s default MIDI driver does not support SysEx messages, or more precisely, as you noticed: No MIDI messages longer than 3 bytes. According to Andrew this has been addressed and will be available in Rack v2.

https://github.com/VCVRack/Rack/issues/1433#issuecomment-559625345

Writing you own MIDI driver is possible, I did write two myself (one “Loopback” driver for testing purposes, one for Expert Sleepers ESX-GT8).

MIDI drivers in plugins?

As it got mentioned in the development blog: Here is a first look at the MIDI driver. Each instance (up to 4) of the ES MIDI module creates 8 ports in the MIDI driver. The output ports should be connected to the Expert Sleepers 8GT module. It is essentially the same as “CV to MIDI” but this way you can send any MIDI message using the existing modules. For debugging porposes I created a specialized scope to review the bits of the encoded MIDI messages. [Img…

There are two caveats though:

A bug in Rack v1.1.6 causes a crash on exit if you register your own MIDI driver. It can be easily fixed in a custom build of Rack but the last official version will crash.

https://github.com/VCVRack/Rack/issues/1735

Second, the rtmidi-instances are not accessible through Rack’s API. If you want you own MIDI driver with SysEx support you need to instanciate and connect rtmidi in your plugin. I don’t know how much work this would be or if it’s even feasible. It might be easier to use your own build of Rack which supports SysEx natively.

In Rack v1 this topic is a bit of a dead end, I’m afraid. At least if rely on the official build v1.1.6.