WiringPi/examples/delayTest.c

#include <stdio.h>
#include <unistd.h>
#include <wiringPi.h>

#include <sys/time.h>

#define	CYCLES	1000

int main()
{
  int x ;
  struct timeval t1, t2 ;
  int t ;
  int max, min ;
  int del ;
  int underRuns, overRuns, exactRuns, total ;
  int descheds ;

  if (wiringPiSetup () == -1)
    return 1 ;

  piHiPri (10) ; sleep (1) ;

// Baseline test

  gettimeofday (&t1, NULL) ;
  gettimeofday (&t2, NULL) ;

  t = t2.tv_usec - t1.tv_usec ;
  printf ("Baseline test: %d\n", t);

  for (del = 1 ; del < 200 ; ++del)
  {
    underRuns = overRuns = exactRuns = total = 0 ;
    descheds = 0 ;
    max = del ;
    min = del ;

    for (x = 0 ; x < CYCLES ; ++x)
    {
      for (;;)				// Repeat this if we get a delay over 999uS
      {					// -> High probability Linux has deschedulled us
	gettimeofday (&t1, NULL) ;
	  delayMicroseconds (del) ;
	gettimeofday (&t2, NULL) ;

	if (t2.tv_usec < t1.tv_usec)	// Counter wrapped
	  t = (1000000 + t2.tv_usec) - t1.tv_usec;
	else
	  t = t2.tv_usec - t1.tv_usec ;
	if (t > 999)
	{
	  ++descheds ;
	  continue ;
	}
	else
	  break ;
      }

      if (t > max)
      {
        max = t ;
	++overRuns ;
      }
      else if (t < min)
      {
	min = t ;
	++underRuns ;
      }
      else
	++exactRuns ;

      total += t ;
    }
    printf ("Delay: %3d. Min: %3d, Max: %3d, Unders: %3d, Overs: %3d, Exacts: %3d, Average: %3d,  Descheds: %2d\n",
	del, min, max, underRuns, overRuns, exactRuns, total / CYCLES,  descheds) ;
    fflush (stdout) ;
    delay (1) ;
  }

  return 0 ;
}