#include <stdio.h>
#include <unistd.h>
#include <time.h>
#include <sys/time.h>
#include <fcntl.h>
#include <string.h>
#include <sched.h>

#define DAQ_NAME "/dev/daq"

/* example of periodic task */

void timespec_add_ns(struct timespec *t, unsigned long long ns) {
  int tmp = ns / 1000000000;
  t->tv_sec += tmp;
  ns -= tmp * 1000000000;
  t->tv_nsec += ns;

  tmp = t->tv_nsec / 1000000000;
  t->tv_sec += tmp;
  t->tv_nsec -= tmp * 1000000000;
}

int main(const int argc, const char * argv[])
{
  int gfd, voltage, Cycle, Cycle_ms, Period, Off_Cycle;

  struct timespec timer;
  struct sched_param param;

  if ((gfd = open (DAQ_NAME, O_RDWR)) < 0) {
    perror ("open: " DAQ_NAME);
    return -1;
  }

  Cycle_ms = 3;
  if (argc > 1) {
    Period = (int) strtol(argv[1], NULL, 10)/ Cycle_ms; 
    Off_Cycle = (int) strtol(argv[2], NULL, 10) / Cycle_ms; 
  } else {
    Period = 280 / Cycle_ms;
    Off_Cycle = 10 / Cycle_ms;
  }

  /* set the priority of the task (high priority) */
  param.sched_priority = sched_get_priority_max(SCHED_FIFO);
  sched_setscheduler(0, SCHED_FIFO, &param);

  Cycle = 0;
  clock_gettime(CLOCK_REALTIME, &timer);
  for (;;) {
    if (Cycle == 0) {
      voltage = 4;
      write(gfd, &voltage, 2);
    } else if (Cycle == Off_Cycle) {
      voltage = 0;
      write(gfd, &voltage, 2);
    }
    timespec_add_ns(&timer, Cycle_ms * 1000000);
    clock_nanosleep(CLOCK_REALTIME, TIMER_ABSTIME, &timer, NULL);
    Cycle++;
    if (Cycle == Period) Cycle = 0;
   }
  return 0;
}