test_rtc.c

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

int main() {
  int fd = open("/dev/rtc0", O_RDONLY);
  if(fd == -1) {
    printf("Error opening /dev/rtc0\n");
    return 1;
  }

  struct rtc_time rtc_tm;

  printf("Reading previous alarm\n");
  if(ioctl(fd, RTC_ALM_READ, &rtc_tm) == -1) {
    printf("Error reading alarm\n");
    return 1;
  }
  printf("Previous RTC alarm date/time is %d-%d-%d, %02d:%02d:%02d.\n",
         rtc_tm.tm_year + 1900, rtc_tm.tm_mon + 1, rtc_tm.tm_mday,
         rtc_tm.tm_hour, rtc_tm.tm_min, rtc_tm.tm_sec);

  printf("Reading current time\n");
  if(ioctl(fd, RTC_RD_TIME, &rtc_tm) == -1) {
    printf("Error reading current time\n");
    return 1;
  }

  printf("Current RTC date/time is %d-%d-%d, %02d:%02d:%02d.\n",
         rtc_tm.tm_year + 1900, rtc_tm.tm_mon + 1, rtc_tm.tm_mday,
         rtc_tm.tm_hour, rtc_tm.tm_min, rtc_tm.tm_sec);

  printf("Setting alarm\n");
  rtc_tm.tm_sec += 10;
  if (rtc_tm.tm_sec >= 60) {
    rtc_tm.tm_sec %= 60;
    rtc_tm.tm_min++;
  }
  if (rtc_tm.tm_min == 60) {
    rtc_tm.tm_min = 0;
    rtc_tm.tm_hour++;
  }
  if (rtc_tm.tm_hour == 24) {
    rtc_tm.tm_hour = 0;
  }

  printf("Alarm date/time is %d-%d-%d, %02d:%02d:%02d.\n",
         rtc_tm.tm_year + 1900, rtc_tm.tm_mon + 1, rtc_tm.tm_mday,
         rtc_tm.tm_hour, rtc_tm.tm_min, rtc_tm.tm_sec);

  if(ioctl(fd, RTC_ALM_SET, &rtc_tm) == -1) {
    printf("Error setting alarm\n");
    return 1;
  }

  printf("Enabling alarm interrupts\n");
  if(ioctl(fd, RTC_AIE_ON, 0) == -1) {
    printf("Error enabling alarm interrupt\n");
    return 1;
  }

  printf("Reading alarm back\n");
  if(ioctl(fd, RTC_ALM_READ, &rtc_tm) == -1) {
    printf("Error reading alarm\n");
    return 1;
  }
  printf("Current RTC alarm date/time is %d-%d-%d, %02d:%02d:%02d.\n",
         rtc_tm.tm_year + 1900, rtc_tm.tm_mon + 1, rtc_tm.tm_mday,
         rtc_tm.tm_hour, rtc_tm.tm_min, rtc_tm.tm_sec);

  printf("Enabling alarm interrupts AGAIN\n");
  if(ioctl(fd, RTC_AIE_ON, 0) == -1) {
    printf("Error enabling alarm interrupt AGAIN\n");
    return 1;
  }

  printf("Flushing I/O...\n");
  sync();
  fflush(stdout);
  usleep(10 * 1000);

  printf("Waiting for alarm...\n");
  unsigned long dummy;
  if(read(fd, &dummy, sizeof(dummy)) == -1) {
    printf("Error waiting for alarm interrupt\n");
    return 1;
  }
  /*
  printf("Suspending to memory\n");
  int power = open("/sys/power/state", O_WRONLY);
  if(write(power, "mem", 3) == -1) {
    printf("Error suspending\n");
    return 1;
  }
  close(power);
  */
  printf("Alarm detected!\n");

  printf("Disabling alarm interrupts\n");
  if(ioctl(fd, RTC_AIE_OFF, 0) == -1) {
    printf("Error disabling alarm interrupt\n");
    return 1;
  }

  close(fd);
  return 0;
}