gistfile1.c

#include <inttypes.h>
#include <time.h>

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

int diff(struct timespec* ts_prev, struct timespec* ts){
    return (ts->tv_sec - ts_prev->tv_sec) * 1000 + (ts->tv_nsec - ts_prev->tv_nsec) / 1000000;
}

int main(){
    int c = CLOCK_MONOTONIC;
    struct timespec ts, ts_prev;
    struct timespec req;
    req.tv_sec = 0;
    req.tv_nsec = 200*1000000;
    clock_gettime(c, &ts_prev);
    clock_nanosleep(c, 0, &req, NULL);
    for(;;){
        clock_gettime(c, &ts);
        int d = diff(&ts_prev, &ts);
        printf("%d.%d (%d)\n", ts.tv_sec, ts.tv_nsec / 1000000, d);
        if(d > 220 || d < 190)break;
        ts_prev = ts;
        clock_nanosleep(c, 0, &req, NULL);
    }
}