alsagentone.c

/*
 * File: alsagentone.c
 * Tone generator from alsa audio api
 * Author: Coolbrother
 * Date: 31/12/2020
 * */

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

#define BUF_LEN 48000
#define DEF_FREQ 440
#define DEF_DUR 1
float g_buffer[BUF_LEN];
snd_pcm_t *g_handle;
snd_pcm_sframes_t g_frames;
int channels =1;
snd_pcm_format_t format = SND_PCM_FORMAT_FLOAT;
int rate = 48000;


float* genTone(float freq) {
    // must create a pointer to return buffer
    // float *buf = malloc(sizeof(float) * BUF_LEN);
    float vol =1;
    float t = 2*M_PI*freq/(rate*channels);
    // int nbSamples = rate * channels * dur;
    // printf("nbSamples: %d\n", nbSamples);
    int maxSamp = 32767;
    float* buf = g_buffer;
    for (int i=0; i< BUF_LEN; i++) {
        // val = (int)maxSamp*vol*sin(t*i);
        g_buffer[i] = sin(t*i);
    }

    return g_buffer;
}
//-----------------------------------------

int openDevice() {
    // open sound device and set params
 	  const static char *device = "default";
	  snd_output_t *output = NULL;
   int err;

    if ((err = snd_pcm_open(&g_handle, device, SND_PCM_STREAM_PLAYBACK, 0)) < 0) {
      fprintf(stderr, "AlsaGenTone: Playback open error: %s\n", snd_strerror(err));
      return EXIT_FAILURE;
    }

    if ((err = snd_pcm_set_params(g_handle,
        format,
        // SND_PCM_FORMAT_S16_LE,
        SND_PCM_ACCESS_RW_INTERLEAVED,
        channels,
        // BUF_LEN,
        rate,
        1, /* period */
        500000)) < 0) {	 /* latency: 0.5sec */ 
      fprintf(stderr, "AlsaGenTone: Playback open error: %s\n", snd_strerror(err));
      return EXIT_FAILURE;
    }

}
//-----------------------------------------

void closeDevice() {
    // closing sound device
    // necessary to flush and send short sample
    snd_pcm_drain(g_handle);
	  snd_pcm_close(g_handle);

}
//-----------------------------------------

void writeBuf(float* buf, int nbFrames, int nbTimes) {
  for (int i=0; i < nbTimes; i++) {
      // Sending the sound
      g_frames += snd_pcm_writei(g_handle, buf, nbFrames);
  }
  // printf("WriteBuf nbFrames: %d\n", g_frames);

}
//-----------------------------------------

void playFreq(float freq, float dur) {
    // playing one freq
    float* buf;
    int nbSamples = rate * channels * dur;
    int nbTimes = nbSamples / BUF_LEN;
    int restFrames = nbSamples % BUF_LEN;
    // printf("restFrames: %d\n", restFrames);
    if (nbSamples >0) {
        buf = genTone(freq);
        if (nbTimes >0) {
            writeBuf(buf, BUF_LEN, nbTimes);	
        }
        if (restFrames > 0) {
            writeBuf(buf, restFrames, 1);
        }
    
    }
    // printf("nbFrames: %d\n", g_frames);

}
//-----------------------------------------

int main(int argc, char *argv[]) {
    int err;
    float freq = DEF_FREQ; // in hertz
    float dur = DEF_DUR; // in seconds
    
    freq = (argc > 1) ? atof(argv[1]) : DEF_FREQ;
    if (freq == 0) {
        fprintf(stderr, "AlsaGenTone: Invalid frequency.\n");
        return EXIT_FAILURE;
    }

    dur = (argc > 2) ? atof(argv[2]) : DEF_DUR;
    if (dur == 0) {
        fprintf(stderr, "AlsaGenTone: Invalid duration.\n");
        return EXIT_FAILURE;
    }
    
    if (err = openDevice()) {
        return EXIT_FAILURE;
    }
    
    // SINE WAVE
    printf("Playing freq, Sine tone at %.3fHz during %.3f secs.\n", freq, dur);
    playFreq(freq, dur);

    closeDevice();

    return EXIT_SUCCESS;
}
//-----------------------------------------