#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <time.h>

int main( int argc, char **argv )
{
  int fd_gpio;
  int value;
  struct timespec sleeptime;

  fd_gpio=open("/dev/fastgpio4",O_WRONLY);
  if (fd_gpio<0) {
      printf("kann GPIO nicht oeffnen\n");
      return -1;
  }

  sleeptime.tv_sec = 0;
  sleeptime.tv_nsec= 500000000;
  while (1) {
      value = 1;
      write(fd_gpio,&value,sizeof(value));
      clock_nanosleep( CLOCK_MONOTONIC, 0,
            &sleeptime, NULL );
      value = 0;
      write(fd_gpio,&value,sizeof(value));
      clock_nanosleep( CLOCK_MONOTONIC, 0,
            &sleeptime, NULL );
  }
  return 0;
}