#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <sys/ioctl.h>
#include <linux/rtc.h>

int
main(int argc, char* argv[])
{
   int fd;
   int err;
   unsigned long v;

   fd = open("/dev/rtc", O_RDWR | O_NONBLOCK);
   if (fd == -1) {
      perror("Cannot open /dev/rtc");
      return 1;
   }
   err = ioctl(fd, RTC_IRQP_SET, 8192);
   if (err) {
      perror("Cannot set 1kHz timer");
      return 1;
   }
   err = ioctl(fd, RTC_PIE_ON);
   if (err) {
      perror("Cannot start periodic interrupt");
      return 1;
   }
   err = read(fd, &v, sizeof v);
   if (err != sizeof v) {
      if (err != -1 || errno != EAGAIN) {
         perror("Cannot flush interrupt count");
         return 1;
      }
   }
   sleep(1);
   err = read(fd, &v, sizeof v);
   if (err != sizeof v) {
      perror("Cannot retrieve interrupt count after 1 second");
      return 1;
   }
   printf("Read: %lu-%02lX\n", v / 256, v & 0xFF);
   close(fd);
   return 0;
}