#include <stdio.h>
#include <sys/timex.h>
#include <time.h>
#include <unistd.h>

#define DIFFTS(a, b) ((a.tv_sec - b.tv_sec) + 1e-9 * (a.tv_nsec - b.tv_nsec))

int main() {
	struct timespec ts1, ts2, ts3, ts4 = {0};
	struct timex t;

	t.modes = ADJ_TICK;
	t.tick = 9000;
	if (adjtimex(&t) < 0)
		return 1;

	while (1) {
		clock_gettime(CLOCK_REALTIME, &ts1);
		clock_gettime(CLOCK_MONOTONIC_RAW, &ts2);

		if (ts4.tv_sec)
			printf("freq offset = %.0f ppm\n",
				(DIFFTS(ts1, ts3) / DIFFTS(ts2, ts4) - 1.0) * 1e6);

		ts3 = ts1;
		ts4 = ts2;
		usleep(1000000);
	}

	return 0;
}