MIOS C Example

Filter out all MIDI events which are not sent on Channel #1

We want to create a MIDI filter, which only forwards MIDI events which are sent over MIDI Channel #1.

Copy the SDCC skeleton into a new directory, open the main.c file and enhance the hooks like described below. Thereafter type "make" in the command shell, and upload the new project.hex file to the core.

///////////////////////////////////////////////////////////////////////////// // This function is called by MIOS when a complete MIDI event has been received ///////////////////////////////////////////////////////////////////////////// void MPROC_NotifyReceivedEvnt( unsigned char evnt0, unsigned char evnt1, unsigned char evnt2) __wparam { // check MIDI channel, it should be 0 (-> channel #1) if( (evnt0 & 0x0f) == 0 ) { // before forwarding, we have to differ between 2-byte and 3-byte MIDI events! // for understanding the MIDI coding, please refer to the MIDI spec // (-> http://www.borg.com/~jglatt/tech/midispec.htm) switch( evnt0 & 0xf0 ) { case 0x80: // Note-Off: 3 bytes case 0x90: // Note-On: 3 bytes case 0xa0: // Aftertouch: 3 bytes case 0xb0: // CC: 3 bytes case 0xe0: // Pitchbend: 3 bytes MIOS_MIDI_TxBufferPut(evnt0); MIOS_MIDI_TxBufferPut(evnt1); MIOS_MIDI_TxBufferPut(evnt2); break; case 0xc0: // Program Change: 2 bytes case 0xd0: // Poly Aftertouch: 2 bytes MIOS_MIDI_TxBufferPut(evnt0); MIOS_MIDI_TxBufferPut(evnt1); break; default: // note: status messages must be handled within MPROC_NotifyReceivedByte() break; } } }

If SysEx or Realtime messages should be forwarded as well, then you need to enhance the MPROC_NotifyReceivedByte() function like shown below:

///////////////////////////////////////////////////////////////////////////// // This function is called by MIOS when a MIDI byte has been received ///////////////////////////////////////////////////////////////////////////// void MPROC_NotifyReceivedByte(unsigned char byte) __wparam { static char fx_status; // normal MIDI events are forwarded in MPROC_NotifyReceivedEvnt // this function handles sysex and realtime messages if( byte & 0x80 ) { // Status message if( byte >= 0xf0 ) MIOS_MIDI_TxBufferPut(byte); // transfer byte // determine status if( byte == 0xf0 ) { fx_status = 0xff; // forward until 0xf7 } else if( byte == 0xf7 ) { fx_status = 0; // f7 reached, no forward } else if( byte == 0xf1 || byte == 0xf3 ) { fx_status = 1; // expecting one additional byte } else if( byte == 0xf2 ) { fx_status = 2; // expecting two additional bytes } else { fx_status = 0; // expecting no additional byte } } else { // check if fx status active if( fx_status ) { // forward data byte MIOS_MIDI_TxBufferPut(byte); // decrement counter if required if( fx_status != 0xff ) --fx_status; } } }

A list of available MIOS function can be found here.

Last update: 2024-05-08