/*
 *	Real Time Clock Driver Test/Example Program
 *
 *	Compile with:
 *		cc -Wall rtctest2.c -o rtctest2
 *
 *	Copyright (C) 2005 Martin Habets.
 *
 *	Released under the GNU General Public License, version 2,
 *	included herein by reference.
 *
 */

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

#define LOOPCNT		20

int main(void) {
	int i, fd, retval, irqcount = 0;
	unsigned long tmp, data;
	struct timeval tv1, tv2;
	unsigned long diff, loopdiff, looplen, deviation;

	fd = open ("/dev/rtc", O_RDONLY);
	if (fd ==  -1) {
		perror("/dev/rtc");
		exit(errno);
	}

	/* Read periodic IRQ rate */
	retval = ioctl(fd, RTC_IRQP_READ, &tmp);
	if (retval == -1) {
		perror("ioctl");
		exit(errno);
	}
	fprintf(stderr, "Periodic IRQ rate was %ldHz.\n\n", tmp);
	fflush(stderr);

	/* The frequencies 128Hz, 256Hz, ... 8192Hz are only allowed for root. */
	for (tmp=2; tmp<=8192; tmp*=2) {

		retval = ioctl(fd, RTC_IRQP_SET, tmp);
		if (retval == -1) {
			fprintf(stderr, "\n");
			perror("ioctl");
			break;
		}

		/* Enable periodic interrupts */
		retval = ioctl(fd, RTC_PIE_ON, 0);
		if (retval == -1) {
			perror("ioctl");
			exit(errno);
		}

		retval = gettimeofday(&tv1, NULL);
		if (retval == -1) {
			perror("gettimeofday");
			exit(errno);
		}

		for (i=1; i<=LOOPCNT; i++) {
			/* This blocks */
			retval = read(fd, &data, sizeof(unsigned long));
			if (retval == -1) {
				perror("read");
				exit(errno);
			}
			irqcount++;
		}

		retval = gettimeofday(&tv2, NULL);
		if (retval == -1) {
			perror("gettimeofday");
			exit(errno);
		}

		/* Disable periodic interrupts */
		retval = ioctl(fd, RTC_PIE_OFF, 0);
		if (retval == -1) {
			perror("ioctl");
			exit(errno);
		}

		diff = (tv2.tv_sec-tv1.tv_sec)*1000000 + tv2.tv_usec - tv1.tv_usec;
		loopdiff = diff/20;
		looplen = 1000000/tmp;
		deviation = abs(loopdiff-looplen);
		fprintf(stderr, "20 loops at %ldHz = %ld usec, %ld usec/loop. ",
			tmp, diff, loopdiff);
		fprintf(stderr, "deviation is %ld usec (%d%%).\n", deviation,
			(int)(100*deviation/looplen));
		fflush(stderr);
	}

	fprintf(stderr, "Test complete\n");

	close(fd);
	return 0;
} /* end main */