sesqpa.c

// The MIT License (MIT)
// 
// Copyright (c) 2019 vnullptr
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

#include <stdio.h>
#include <stdarg.h>
#include <math.h>
#include <alloca.h>
#include <pulse/pulseaudio.h>
#include <pulse/simple.h>

#define M_PI 3.14159265358979323846
double sign(double x) {
  if (x > 0.0) return 1.0;
  if (x < 0.0) return -1.0;
  return x;
}

// sampling rate: 48kHz, nyquist frequency: 24kHz
#define NB_SAMPLES 48000

static const pa_sample_spec sample_spec = {
    .format = PA_SAMPLE_S16LE,
    .rate = NB_SAMPLES,
    .channels = 1
};

/* Increments based on the sample of the signal. */
float square_wave( 
    float frequency, 
    float time
) {
    // Equation: "sgn(sin(2πft))"
    return sign(sin(2 * M_PI * frequency * time));
}

float sine_wave( 
    float frequency, 
    float time
) {
    // Equation: "sin(2πft)"
    return sin(2 * M_PI * frequency * time);
}
int error_ret;


void abort_(const char * s, ...)
{
        va_list args;
        va_start(args, s);
        vfprintf(stderr, s, args);
        fprintf(stderr, "\n");
        va_end(args);
        abort();
}


int main(int argc, char** argv) {
    uint32_t frequency = atoi(argv[1]);

    int16_t *sample_buffer;
    size_t  nb_samples = NB_SAMPLES;

    // Allocate the sample buffer to store data.
    sample_buffer = alloca(NB_SAMPLES * sizeof(int16_t));

    pa_simple *pa_ctx;
    pa_usec_t  latency;

    pa_ctx = pa_simple_new(
        NULL,
        argv[0], 
        PA_STREAM_PLAYBACK, 
        NULL, 
        "playback", 
        &sample_spec, 
        PA_CHANNEL_MAP_DEFAULT, 
        NULL, 
        &error_ret
    );
    
    /* If the context is failed to allocate. */
    if(pa_ctx == NULL)
        abort_("Audio context creation is failed: %s", pa_strerror(error_ret));

    for(;;) {
        latency = pa_simple_get_latency(pa_ctx, NULL);

        /* The latency value should not be below zero. */
        if(latency < 0)
            abort_("Negative latency: %s", pa_strerror(error_ret));


        // fill the buffer with square wave
        for(size_t s = 0; s < NB_SAMPLES; ++s)
            sample_buffer[s] = sine_wave(frequency, (float)s/(float)NB_SAMPLES) * 32767.0;

        
        pa_simple_write(pa_ctx, sample_buffer, NB_SAMPLES*sizeof(int16_t), &error_ret);
    
        /* If the number of bytes written is negative it means that it is falied to write. */
        if(error_ret < 0)
            abort_("Audio playback is failed: %s", pa_strerror(error_ret));
    }

finish:
    pa_simple_free(pa_ctx);
}