9. MIDI Development.
For those looking to develop MIDI applications, good examples are often needed to get you started.
The following examples were posted to the LAD mailing list in a thread about examples and documentation/tutorials.
9.1 Example 1
Below is a little sequencer routine from Dr. Matthias Nagorni. More examples can be obtained from Matthias's site which is listed in the Links section.
You compile it like so:
[phil@beatbox] $ gcc seqdemo.c -o seqdemo -lasound
#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, "hw", SND_SEQ_OPEN_DUPLEX, 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);
}
}
}
9.2 Example 2
Below is a ALSA 0.9 MIDI redirector by Nick Dowell.
/* ALSA Sequencer MIDI redirector.
Redirects the input to outputs determined by the MIDI channel
(as requested by Nathaniel Virgo on Linux-Audio-Dev ;-)
based on Dr. Matthias Nagorni's ALSA seq example
Nick Dowell <nixx@nixx.org.uk>
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <alsa/asoundlib.h>
int
main()
{
snd_seq_t *seq_handle;
snd_seq_event_t *ev;
int i;
int portid; /* input port */
int oportid[16]; /* output ports */
int npfd;
struct pollfd *pfd;
char txt[20];
if (snd_seq_open(&seq_handle, "hw", SND_SEQ_OPEN_DUPLEX, 0) < 0) {
fprintf(stderr, "Error opening ALSA sequencer.\n");
exit(1);
}
snd_seq_set_client_name(seq_handle, "MIDI Redirect");
/* open one input port */
if ((portid = snd_seq_create_simple_port
(seq_handle, "Input",
SND_SEQ_PORT_CAP_WRITE | SND_SEQ_PORT_CAP_SUBS_WRITE,
SND_SEQ_PORT_TYPE_APPLICATION)) < 0) {
fprintf(stderr, "fatal error: could not open input port.\n");
exit(1);
}
/* open 16 output ports for the MIDI channels */
for (i=0; i<16; i++){
sprintf( txt, "MIDI Channel %d", i );
if ((oportid[i] = snd_seq_create_simple_port
(seq_handle, txt,
SND_SEQ_PORT_CAP_READ | SND_SEQ_PORT_CAP_SUBS_READ,
SND_SEQ_PORT_TYPE_APPLICATION)) < 0) {
fprintf(stderr, "fatal error: could not open output port.\n");
exit(1);
}
}
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) /* main loop */
if (poll(pfd, npfd, 1000000) > 0){
do {
snd_seq_event_input(seq_handle, &ev);
snd_seq_ev_set_source( ev, oportid[ev->data.control.channel] );
snd_seq_ev_set_subs( ev );
snd_seq_ev_set_direct( ev );
snd_seq_event_output_direct( seq_handle, ev );
snd_seq_free_event(ev);
} while (snd_seq_event_input_pending(seq_handle, 0) > 0);
}
return 0;
}
9.3 Example 3
Below is an example of writing data to the OSS /dev/midi interface by Craig Stuart Sapp.
More examples can be found at Craig's site listed in the Links section.
//
// Programmer: Craig Stuart Sapp [craig@ccrma.stanford.edu]
// Creation Date: Mon Dec 21 18:00:42 PST 1998
// Last Modified: Mon Dec 21 18:00:42 PST 1998
// Filename: ...linuxmidi/output/method1.c
// Syntax: C
// $Smake: gcc -O -o devmidiout devmidiout.c && strip devmidiout
//
#include <linux/soundcard.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
int main(void) {
char* device = "/dev/midi" ;
unsigned char data[3] = {0x90, 60, 127};
// step 1: open the OSS device for writing
int fd = open(device, O_WRONLY, 0);
if (fd < 0) {
printf("Error: cannot open %s\n", device);
exit(1);
}
// step 2: write the MIDI information to the OSS device
write(fd, data, sizeof(data));
// step 3: (optional) close the OSS device
close(fd);
return 0;
}
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