Ru Vuott wrote:

I would like to know how I can ask ALSA to invoke a "Callback" function when an Midi event arrives from an extern-device.

This is not possible.

The mechanism usually used for this is to check for events from the MIDI device in the main message loop (which must be based on poll() or select()).

Are you using raw MIDI or sequencer devices? How does your program's event handling work?

Regards, Clemens