alsa.h

/* public domain Simple, Minimalistic, Audio library for ALSA
 *	©2017 Yuichiro Nakada
 *
 * Basic usage:
 *	AUDIO a;
 *	AUDIO_init(&a, "plughw:PCH,0", 48000, 2, 32); // device, 48000 samplerate, 2 channels, 32 frame
 *	...
 *	int f = AUDIO_frame(&a); // audio data in a.buffer
 *	...
 *	AUDIO_close(&a);
 *
 * */

// Use the newer ALSA API
#define ALSA_PCM_NEW_HW_PARAMS_API
#include <alsa/asoundlib.h>

typedef struct {
	snd_pcm_t *handle;
	snd_pcm_uframes_t frames;
	char *buffer;
	int size;
} AUDIO;

int AUDIO_init(AUDIO *thiz, char *dev, unsigned int val, int ch, int frames, int flag)
{
	// Open PCM device.
	int rc = snd_pcm_open(&thiz->handle, dev, flag ? SND_PCM_STREAM_PLAYBACK : SND_PCM_STREAM_CAPTURE, 0);
	if (rc < 0) {
		fprintf(stderr, "unable to open pcm device '%s' (%s)\n", dev, snd_strerror(rc));
		return 1;
	}

	// Allocate a hardware parameters object.
	snd_pcm_hw_params_t *params;
	snd_pcm_hw_params_alloca(&params);

	// Fill it in with default values.
	snd_pcm_hw_params_any(thiz->handle, params);

	// Set the desired hardware parameters.
	// Interleaved mode
	rc = snd_pcm_hw_params_set_access(thiz->handle, params, SND_PCM_ACCESS_RW_INTERLEAVED);
	if (rc < 0) {
		fprintf(stderr, "cannot set access type (%s)\n", snd_strerror(rc));
		snd_pcm_drain(thiz->handle);
		snd_pcm_close(thiz->handle);
		return 1;
	}

	// Signed 16-bit little-endian format
	rc = snd_pcm_hw_params_set_format(thiz->handle, params, SND_PCM_FORMAT_S16_LE);
	if (rc < 0) {
		fprintf(stderr, "cannot set sample format (%s)\n", snd_strerror(rc));
		snd_pcm_drain(thiz->handle);
		snd_pcm_close(thiz->handle);
		return 1;
	}

	// Channels
	rc = snd_pcm_hw_params_set_channels(thiz->handle, params, ch);
	if (rc < 0) {
		fprintf(stderr, "cannot set channel count (%s)\n", snd_strerror(rc));
		snd_pcm_drain(thiz->handle);
		snd_pcm_close(thiz->handle);
		return 1;
	}

	// 44100 bits/second sampling rate (CD quality)
	int dir;
	rc = snd_pcm_hw_params_set_rate_near(thiz->handle, params, &val, &dir);
	if (rc < 0) {
		fprintf(stderr, "cannot set sample rate (%s)\n", snd_strerror(rc));
		snd_pcm_drain(thiz->handle);
		snd_pcm_close(thiz->handle);
		return 1;
	}

	// Set period size to 32 frames.
	thiz->frames = frames;
	snd_pcm_hw_params_set_period_size_near(thiz->handle, params, &thiz->frames, &dir);

	// Write the parameters to the driver
	rc = snd_pcm_hw_params(thiz->handle, params);
	if (rc < 0) {
		fprintf(stderr, "unable to set parameters (%s)\n", snd_strerror(rc));
		snd_pcm_drain(thiz->handle);
		snd_pcm_close(thiz->handle);
		return 1;
	}

	// Use a buffer large enough to hold one period
	snd_pcm_hw_params_get_period_size(params, &thiz->frames, &dir);
	thiz->size = thiz->frames * 2 * ch; /* 2 bytes/sample, 2 channels */
	thiz->buffer = (char*)malloc(thiz->size);

	snd_pcm_hw_params_get_period_time(params, &val, &dir);
	return 0;
}

int AUDIO_frame(AUDIO *thiz)
{
	int rc = snd_pcm_readi(thiz->handle, thiz->buffer, thiz->frames);
	if (rc == -EPIPE) {
		// EPIPE means overrun
		fprintf(stderr, "overrun occurred\n");
		snd_pcm_prepare(thiz->handle);
	} else if (rc < 0) {
		fprintf(stderr, "read failed (%s)\n", snd_strerror(rc));
	} else if (rc != (int)thiz->frames) {
		fprintf(stderr, "short read, read %d frames\n", rc);
	}
	return rc;
}

int AUDIO_play(AUDIO *thiz, char *data, int frames)
{
	int rc = snd_pcm_writei(thiz->handle, data, frames);
	if (rc == -EPIPE) {
		// EPIPE means overrun
		fprintf(stderr, "overrun occurred\n");
		snd_pcm_recover(thiz->handle, rc, 0);
		//snd_pcm_prepare(thiz->handle);
	} else if (rc < 0) {
		fprintf(stderr, "write failed (%s)\n", snd_strerror(rc));
	} else if (rc != frames) {
		fprintf(stderr, "short write, write %d/%d frames\n", rc, (int)thiz->frames);
	}
	return rc;
}

int AUDIO_play0(AUDIO *thiz)
{
	return AUDIO_play(thiz, thiz->buffer, thiz->frames);
}

void AUDIO_wait(AUDIO *thiz, int msec)
{
	snd_pcm_wait(thiz->handle, msec);
}

void AUDIO_close(AUDIO *thiz)
{
	snd_pcm_drain(thiz->handle);
	snd_pcm_close(thiz->handle);
	free(thiz->buffer);
}