1 files changed, 165 insertions, 0 deletions
diff --git a/metronome.c b/metronome.c
new file mode 100644
index 0000000..d30b61e
--- /dev/null
+++ b/metronome.c
@@ -0,0 +1,165 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+#include <math.h>
+#include <errno.h>
+#include <time.h>
+#include <sys/time.h>
+#include <alsa/asoundlib.h>
+
+#define SAMPLE_RATE 8000
+
+#define BUFFER_SIZE 512
+
+/* 2 bytes per sample; 0.1 seconds long */
+#define TONE_SIZE (2*SAMPLE_RATE/10)
+
+#define TONE1_FREQ 800
+#define TONE2_FREQ 440
+
+static uint8_t tone1[TONE_SIZE];
+static uint8_t tone2[TONE_SIZE];
+static const uint8_t silence[BUFFER_SIZE];
+
+static int set_params(snd_pcm_t *pcm_handle)
+{
+	snd_pcm_hw_params_t *hwparams;
+	unsigned int rate = SAMPLE_RATE;
+	snd_pcm_uframes_t bufsize = BUFFER_SIZE;
+
+	snd_pcm_hw_params_alloca(&hwparams);
+
+	if (snd_pcm_hw_params_any(pcm_handle, hwparams) < 0) {
+		printf("Failed configuring device\n");
+		return -1;
+	}
+	if (snd_pcm_hw_params_set_access(pcm_handle, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED) < 0) {
+		printf("Failed setting access mode\n");
+		return -1;
+	}
+	if (snd_pcm_hw_params_set_format(pcm_handle, hwparams, SND_PCM_FORMAT_S16_LE) < 0) {
+		printf("Failed setting format\n");
+		return -1;
+	}
+	if (snd_pcm_hw_params_set_rate_near(pcm_handle, hwparams, &rate, 0) < 0) {
+		printf("Failed setting sample rate\n");
+		return -1;
+	}
+	if (snd_pcm_hw_params_set_buffer_size_near(pcm_handle, hwparams, &bufsize) < 0) {
+		printf("Failed setting sample rate\n");
+		return -1;
+	}
+	if (snd_pcm_hw_params_set_channels(pcm_handle, hwparams, 1) < 0) {
+		printf("Failed setting channel number\n");
+		return -1;
+	}
+	if (snd_pcm_hw_params(pcm_handle, hwparams) < 0) {
+		printf("Failed applying hardware parameters\n");
+		return -1;
+	}
+
+	return 0;
+}
+
+static void prepare_tones()
+{
+	int i, amplitude = 20;
+	uint16_t sample;
+
+	for(i=0; i<TONE_SIZE-1; i++) {
+		sample = amplitude * sin(2*M_PI*TONE1_FREQ*i/SAMPLE_RATE);
+		tone1[i] = sample % 256;
+		tone1[i+1] = sample >> 8;
+		sample = amplitude * sin(2*M_PI*TONE2_FREQ*i/SAMPLE_RATE);
+		tone2[i] = sample % 256;
+		tone2[i+1] = sample >> 8;
+	}
+}
+
+static long timediff_us(struct timespec *ts1, struct timespec *ts2)
+{
+	struct timeval tv1, tv2, diff;
+
+	TIMESPEC_TO_TIMEVAL(&tv1, ts1);
+	TIMESPEC_TO_TIMEVAL(&tv2, ts2);
+
+	timersub(&tv1, &tv2, &diff);
+
+	return diff.tv_sec * 1000000 + diff.tv_usec;
+}
+
+static void play_tone(snd_pcm_t *pcm_handle, char tone)
+{
+	const uint8_t *tonebuf;
+	int tonebuf_size;
+
+	switch(tone) {
+		case '1':
+			tonebuf = tone1;
+			tonebuf_size = sizeof(tone1);
+			break;
+		case '2':
+			tonebuf = tone2;
+			tonebuf_size = sizeof(tone2);
+			break;
+		case 's':
+		default:
+			tonebuf = silence;
+			tonebuf_size = sizeof(silence);
+			break;
+	}
+	while (snd_pcm_writei(pcm_handle, tonebuf, tonebuf_size / 2) < 0) {
+		snd_pcm_prepare(pcm_handle);
+		printf("underrun\n");
+	}
+}
+
+static int play(snd_pcm_t *pcm_handle, const char *pattern, int bpm)
+{
+	int i = 0;
+	double period_us;
+	struct timespec cur_t, old_t = {};
+
+	period_us = 1000000 * 60.0 / bpm;
+
+	/* fill buffer with silence */
+	snd_pcm_prepare(pcm_handle);
+	play_tone(pcm_handle, 's');
+
+	while(1) {
+		if (clock_gettime(CLOCK_MONOTONIC, &cur_t) == -1) {
+			printf("Failed getting time: %s\n", strerror(errno));
+			return -1;
+		}
+
+		if (timediff_us(&cur_t, &old_t) >= period_us) {
+			memcpy(&old_t, &cur_t, sizeof(struct timespec));
+			play_tone(pcm_handle, pattern[i++ % strlen(pattern)]);
+		} else {
+			play_tone(pcm_handle, 's');
+		}
+
+		usleep(500);
+	}
+}
+
+int main()
+{
+	snd_pcm_t *pcm_handle;
+
+	if (snd_pcm_open(&pcm_handle, /*"default"*/ "plughw:1,0", SND_PCM_STREAM_PLAYBACK, 0) < 0) {
+		printf("Failed opening device\n");
+		return 1;
+	}
+
+	if (set_params(pcm_handle) < 0) {
+		return 1;
+	}
+
+	prepare_tones();
+	play(pcm_handle, "2111", 120);
+
+	snd_pcm_close(pcm_handle);
+
+	return 0;
+}