Mikkel,
I have done more analysis.
• I forked PGMidi and modified it so that it correctly sets up the virtualDestinationSource.
•
https://github.com/rhoiberg/PGMidi
• Using TouchOSC, the PGMIDIVirtualDestinationReadProc never gets called, even though it shows up in the list of output ports.
• I have tried multiple other applications with the same result.
• Using the MidiMonitor the PGMIDIVirtualDestinationReadProc will get called by tapping the "Send Midi" button.
• I think that it is related to the fact the the MidiMonitor app is in the foreground.
My guess is that there is something about iOS7, that even though I have the audio UIBackgroundMode set, CoreMidi is not calling the static method PGMIDIVirtualDestinationReadProc.
Ring any bells?