
#include <alsa/asoundlib.h>
#include <alsa/seq.h>
#include <sys/time.h>

void normalize(struct timeval *tv)
{
    if (tv->tv_sec == 0) {
        while (tv->tv_usec <= -1000000) { tv->tv_usec += 1000000; --tv->tv_sec; }
        while (tv->tv_usec >=  1000000) { tv->tv_usec -= 1000000; ++tv->tv_sec; }
    } else if (tv->tv_sec < 0) {
        while (tv->tv_usec <= -1000000) { tv->tv_usec += 1000000; --tv->tv_sec; }
        while (tv->tv_usec > 0) { tv->tv_usec -= 1000000; ++tv->tv_sec; }
    } else { 
        while (tv->tv_usec >= 1000000) { tv->tv_usec -= 1000000; ++tv->tv_sec; }
        while (tv->tv_usec < 0) { tv->tv_usec += 1000000; --tv->tv_sec; }
    }
}

int
main()
{
    snd_seq_t *handle;
    int portid;
    //int npfd;
    //struct pollfd *pfd;
    int queue;
    //int i;
    //int rval;
    struct timeval starttv, prevdiff;
    int countdown = -1;
    //snd_seq_queue_timer_t *timer;
    //snd_timer_id_t *timerid;

    if (snd_seq_open(&handle, "hw", SND_SEQ_OPEN_DUPLEX, 0) < 0) {
        fprintf(stderr, "failed to open ALSA sequencer interface\n");
        return 1;
    }

    snd_seq_set_client_name(handle, "generator");

    if ((portid = snd_seq_create_simple_port
            (handle, "generator",
                    SND_SEQ_PORT_CAP_READ | SND_SEQ_PORT_CAP_SUBS_READ, 0)) < 0) {
        fprintf(stderr, "failed to create ALSA sequencer port\n");
        return 1;
    }

    if ((queue = snd_seq_alloc_queue(handle)) < 0) {
        fprintf(stderr, "failed to create ALSA sequencer queue\n");
        return 1;
    }
    /*
    snd_seq_queue_timer_alloca(&timer);
    snd_seq_get_queue_timer(handle, queue, timer);
    snd_timer_id_alloca(&timerid);
    snd_timer_id_set_class(timerid, SND_TIMER_CLASS_PCM);
    snd_timer_id_set_sclass(timerid, SND_TIMER_SCLASS_NONE);
    snd_timer_id_set_card(timerid, 0);
    snd_timer_id_set_device(timerid, 0);
    snd_timer_id_set_subdevice(timerid, 0);
    snd_seq_queue_timer_set_id(timer, timerid);
    snd_seq_set_queue_timer(handle, queue, timer);
     */
    snd_seq_start_queue(handle, queue, 0);
    snd_seq_drain_output(handle);

    gettimeofday(&starttv, 0);
    prevdiff.tv_sec = 0;
    prevdiff.tv_usec = 0;

    while (countdown != 0) {

        snd_seq_queue_status_t *status;
        const snd_seq_real_time_t *rtime;
        struct timeval tv, diff, diffdiff;

        snd_seq_queue_status_alloca(&status);

        snd_seq_get_queue_status(handle, queue, status);
        rtime = snd_seq_queue_status_get_real_time(status);

        gettimeofday(&tv, 0);

        tv.tv_sec -= starttv.tv_sec;
        tv.tv_usec -= starttv.tv_usec;
        normalize(&tv);

        diff.tv_sec = tv.tv_sec - rtime->tv_sec;
        diff.tv_usec = tv.tv_usec - rtime->tv_nsec / 1000;
        normalize(&diff);

        diffdiff.tv_sec = diff.tv_sec - prevdiff.tv_sec;
        diffdiff.tv_usec = diff.tv_usec - prevdiff.tv_usec;
        normalize(&diffdiff);
        prevdiff = diff;

        fprintf(stderr, " real time: %12ld sec %8ld usec\nqueue time: %12u sec %8u usec\n      diff: %12ld sec %8ld usec\n  diffdiff: %12ld sec %8ld usec\n",
                tv.tv_sec, tv.tv_usec,
                rtime->tv_sec, rtime->tv_nsec / 1000,
                diff.tv_sec, diff.tv_usec,
                diffdiff.tv_sec, diffdiff.tv_usec);

        if (diffdiff.tv_usec >  5000 ||
                diffdiff.tv_usec < -5000) {
            fprintf(stderr, "oops! queue slipped\n");
            if (tv.tv_sec < 5) {
                fprintf(stderr, "(ignoring in first few seconds)\n");
            } else {
                countdown = 2;
            }
        } else {
            if (countdown > 0) --countdown;
        }

        fprintf(stderr, "\n");
        struct timespec ts;
        ts.tv_sec = 1;
        ts.tv_nsec = 0;
        nanosleep(&ts, 0);
    }
}

