/* Chirp repeatedly from 6kHz to 10kHz at 2kHz/s at 48ksps (16-bit
 * little-endian 2-channel signed, like DAT).
 *
 make -k chirp LDFLAGS=-lm && ./chirp | play -t raw -r 48000 -s -b 16 -L -c 2 -
 */
#include <math.h>
#include <stdio.h>

int main()
{
  int sampling_rate = 48000;
  double hz
    , hz_per_sec = 2000
    , min_freq = 6000
    , max_freq = 10000
    , theta = 0
    , hz_per_sample = hz_per_sec / sampling_rate
    , amplitude = 32767
  ;

  hz = min_freq;
  for (;;) {
    short sample = amplitude * sin(theta) + 0.5;

    char low_byte = sample & 0xff, high_byte = sample >> 8;
    putchar(low_byte); putchar(high_byte);
    putchar(low_byte); putchar(high_byte);

    theta += 2 * M_PI * hz / sampling_rate;
    hz += hz_per_sample;
    if (hz > max_freq) hz = min_freq;
  }
}