seqdemo.c

alsa sound devlopment

/* seqdemo.c by Matthias Nagorni */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <alsa/asoundlib.h>

snd_seq_t *open_seq();
void midi_action(snd_seq_t *seq_handle);

snd_seq_t *open_seq() {

  snd_seq_t *seq_handle;
  int portid;

  if (snd_seq_open(&seq_handle, "default", SND_SEQ_OPEN_INPUT, 0) < 0) {
    fprintf(stderr, "Error opening ALSA sequencer.\n");
    exit(1);
  }
  snd_seq_set_client_name(seq_handle, "ALSA Sequencer Demo");
  if ((portid = snd_seq_create_simple_port(seq_handle, "ALSA Sequencer Demo",
            SND_SEQ_PORT_CAP_WRITE|SND_SEQ_PORT_CAP_SUBS_WRITE,
            SND_SEQ_PORT_TYPE_APPLICATION)) < 0) {
    fprintf(stderr, "Error creating sequencer port.\n");
    exit(1);
  }
  return(seq_handle);
}

void midi_action(snd_seq_t *seq_handle) {

  snd_seq_event_t *ev;

  do {
    snd_seq_event_input(seq_handle, &ev);
    switch (ev->type) {
      case SND_SEQ_EVENT_CONTROLLER: 
        fprintf(stderr, "Control event on Channel %2d: %5d       \r",
                ev->data.control.channel, ev->data.control.value);
        break;
      case SND_SEQ_EVENT_PITCHBEND:
        fprintf(stderr, "Pitchbender event on Channel %2d: %5d   \r", 
                ev->data.control.channel, ev->data.control.value);
        break;
      case SND_SEQ_EVENT_NOTEON:
        fprintf(stderr, "Note On event on Channel %2d: %5d       \r",
                ev->data.control.channel, ev->data.note.note);
        break;        
      case SND_SEQ_EVENT_NOTEOFF: 
        fprintf(stderr, "Note Off event on Channel %2d: %5d      \r",         
                ev->data.control.channel, ev->data.note.note);           
        break;        
    }
    snd_seq_free_event(ev);
  } while (snd_seq_event_input_pending(seq_handle, 0) > 0);
}

int main(int argc, char *argv[]) {

  snd_seq_t *seq_handle;
  int npfd;
  struct pollfd *pfd;
    
  seq_handle = open_seq();
  npfd = snd_seq_poll_descriptors_count(seq_handle, POLLIN);
  pfd = (struct pollfd *)alloca(npfd * sizeof(struct pollfd));
  snd_seq_poll_descriptors(seq_handle, pfd, npfd, POLLIN);
  while (1) {
    if (poll(pfd, npfd, 100000) > 0) {
      midi_action(seq_handle);
    }  
  }
}