//
// 1hz.exe - Generate 1PPS with sound card.
//
// - 1 PPS output timing is as [in]accurate as the sound card.
//
// - Can be used to determine accuracy (and stability) of the
//   crystal oscillator on the sound card.
//
// - For example, use a TI counter to compare a GPS 1 PPS with
//   the sound card 1 PPS. Collect a few minutes, hours, or even
//   days of data. Compute frequeny error (= phase drfit) or
//   frequency drift (delta f over delta t) or Allan Deviation.
//
// 21-Aug-2005 /tvb
//

#include <stdio.h>
#include <stdlib.h>

void wave_init (void);
void sound_init (void);
void sound_send (void);
void sound_done (void);

int main (int argc, char *argv[])
{
    long duration, i;

    duration = (argc > 1) ? atol(argv[1]) : 10;
    fprintf(stderr, "duration = %ld seconds\n", duration);
    wave_init();
    sound_init();
    for (i = 0; i < duration || duration == 0; i += 1) {
        sound_send();
        fprintf(stderr, ".");
    }
    fprintf(stderr, "\n");
    sound_done();

    return 0;
}

int sps = 44100;
int points = 44100;

#define MAX_SAMPLE_SIZE 44100
unsigned char wave[MAX_SAMPLE_SIZE];

void wave_init (void)
{
    int i;

    for (i = 0; i < points - 1; i += 1) {
        wave[i] = 128;
    }
    wave[i] = 0;
}

// Begin Windows specific code.

#include <windows.h>

#define NBUF 3
int nbuf = NBUF;
HWAVEOUT wo;
WAVEFORMATEX wf;
WAVEHDR wh[NBUF];

#define CHECK_MMSYSERR(s) \
    if (error != MMSYSERR_NOERROR) { \
        fprintf(stderr, "file %s, line %d, %s failed (error %d)\n", \
                __FILE__, __LINE__, #s, error); \
        exit(1); \
    }

// Open sound card and initialize buffer pool.

void sound_init (void)
{
    int buf, error;

    wf.wFormatTag = WAVE_FORMAT_PCM;
    wf.nChannels = 1;
    wf.wBitsPerSample = 8;
    wf.nSamplesPerSec = sps;
    wf.nBlockAlign = wf.nChannels * wf.wBitsPerSample / 8;
    wf.nAvgBytesPerSec = wf.nSamplesPerSec * wf.nBlockAlign;
    wf.cbSize = 0;
    error = waveOutOpen(&wo, 0, &wf, 0, 0, CALLBACK_NULL);
    if (error == MMSYSERR_NOTENABLED || error == MMSYSERR_ALLOCATED) {
        fprintf(stderr, "Sound card busy or not available.\n");
        exit(1);
    }
    CHECK_MMSYSERR(waveOutOpen);

    for (buf = 0; buf < nbuf; buf += 1) {
        if ((wh[buf].lpData = malloc(points)) == NULL) {
            fprintf(stderr, "malloc failed\n");
            exit(1);
        }
        wh[buf].dwBufferLength = points;
        wh[buf].dwFlags = 0;
        wh[buf].dwLoops = 0;
        error = waveOutPrepareHeader(wo, &wh[buf], sizeof wh);
        CHECK_MMSYSERR(waveOutPrepareHeader);
        wh[buf].dwFlags |= WHDR_DONE;
    }
}

// Send a one second wave to the sound card.

void sound_send (void)
{
    int buf, error;

    while (1) {
        for (buf = 0; buf < nbuf; buf += 1) {
            if (wh[buf].dwFlags & WHDR_DONE) {
                memcpy(wh[buf].lpData, wave, points);
                error = waveOutWrite(wo, &wh[buf], sizeof wh);
                CHECK_MMSYSERR(waveOutWrite);
                return;
            }
        }
        _sleep(100);
    }
}

// Close sound card.

void sound_done (void)
{
    int buf, error;

    error = waveOutReset(wo);
    CHECK_MMSYSERR(waveOutReset);

    for (buf = 0; buf < nbuf; buf += 1) {
        error = waveOutUnprepareHeader(wo, &wh[buf], sizeof wh);
        CHECK_MMSYSERR(waveOutUnprepareHeader);
        free(wh[buf].lpData);
    }

    error = waveOutClose(wo);
    CHECK_MMSYSERR(waveOutClose);
}