#include <wiringPi.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define PERIOD 20000
#define STEP 20
#define PAUSE 300000

struct timespec tim;
void Delay(int microsec)
{

 tim.tv_sec = 0;
 tim.tv_nsec = microsec * 1000;
     while(nanosleep(&tim,&tim)==-1)
          continue;
}

int main (void)
{
 int time;
 int i;

  // check wiringPi setup
  if (wiringPiSetup() == -1)
   {
    printf("wiringPi-Error\n");
    exit(1);
   }
   pinMode(1, OUTPUT);

   for(;;)
     {
       for(time=500;time<2500;time=time+STEP)
        {
          printf("%d ms\n", time);fflush(0);
          for(i=0;i<10;i++)
           {
            digitalWrite(1,HIGH);
            Delay(time);
            digitalWrite(1,LOW);
            Delay(PERIOD-time);
           }
          Delay(PAUSE);
        }
    }
}