This is used for closing of a MidiShare driver. MidiShare applications owning a "context alarm" will be informed of this closing using the MIDICloseDriver alarm code.
void MidiUnregisterDriver (short ref);
ref
- a driver reference number, given by the corresponding MidiRegisterDriver call.
when unregistering, a driver should take care of the following: if MidiShare is active at unregister time, it will first put the driver to sleep by calling the driver 'sleep' callback.