Convert Linux keyboard events into ALSA sequencer events

input2seq.c

/* 
 compile with:
	gcc -o input2seq -lasound input2seq.c
*/
#include <linux/input.h>
#include <alsa/asoundlib.h>
#include <fcntl.h>
#include <stdio.h>

//#define INPUT_DEVICE "/dev/input/by-path/platform-i8042-serio-0-event-kbd"
#define INPUT_DEVICE "/dev/input/event2"
#define CHANNEL 0
#define CONTROLLER_SUSTAIN 64
#define CONTROLLER_HOLD2 69
#define CTL_VALUE_ON 127
#define CTL_VALUE_OFF 0

int main(void)
{
	struct input_event ie;
	int fd, port, err;
	snd_seq_t *seq;
	snd_seq_event_t ev;

	fd = open(INPUT_DEVICE, O_RDONLY);
	if (fd == -1) {
		perror(INPUT_DEVICE);
		return 1;
	}
	err = snd_seq_open(&seq, "default", SND_SEQ_OPEN_OUTPUT, 0);
	if (err < 0) {
		fprintf(stderr, "cannot open sequencer: %s\n", snd_strerror(err));
		return 1;
	}
	snd_seq_set_client_name(seq, "Input/MIDI converter");
	port = snd_seq_create_simple_port(seq, "Port 1",
					  SND_SEQ_PORT_CAP_READ |
					  SND_SEQ_PORT_CAP_SUBS_READ,
					  SND_SEQ_PORT_TYPE_MIDI_GENERIC |
					  SND_SEQ_PORT_TYPE_SOFTWARE);
	if (port < 0) {
		fprintf(stderr, "cannot create port: %s\n", snd_strerror(port));
		return 1;
	}
	snd_seq_ev_clear(&ev);
	snd_seq_ev_set_source(&ev, port);
	snd_seq_ev_set_subs(&ev);
	snd_seq_ev_set_direct(&ev);
	for (;;) {
		if (read(fd, &ie, sizeof(ie)) != sizeof(ie))
			break;
		ev.type = SND_SEQ_EVENT_NONE;
		if (ie.type ==  EV_KEY) {
			switch (ie.code) {
			case KEY_UP:
				if (ie.value == 1)
					snd_seq_ev_set_controller(&ev, CHANNEL, CONTROLLER_SUSTAIN, CTL_VALUE_ON);
				else if (ie.value == 0)
					snd_seq_ev_set_controller(&ev, CHANNEL, CONTROLLER_SUSTAIN, CTL_VALUE_OFF);
				break;
			case KEY_DOWN:
				if (ie.value == 1)
					snd_seq_ev_set_controller(&ev, CHANNEL, CONTROLLER_HOLD2, CTL_VALUE_ON);
				else if (ie.value == 0)
					snd_seq_ev_set_controller(&ev, CHANNEL, CONTROLLER_HOLD2, CTL_VALUE_OFF);
				break;
			}
		}
		if (ev.type != SND_SEQ_EVENT_NONE)
			snd_seq_event_output_direct(seq, &ev);
	}
	snd_seq_close(seq);
	close(fd);
	return 0;
}