2 * This program can be used to calibrate the clock reading jitter of a
3 * particular CPU and operating system. It first tickles every element
4 * of an array, in order to force pages into memory, then repeatedly
5 * reads the system clock and, finally, writes out the time values for
6 * later analysis. From this you can determine the jitter and if the
7 * clock ever runs backwards.
20 #define JAN_1970 2208988800UL /* Unix base epoch */
21 #define CLOCK_GETTIME /* Solaris hires clock */
26 void sys_gettime(l_fp *);
36 double dtemp, gtod[NBUF];
39 * Force pages into memory
41 for (i = 0; i < NBUF; i ++)
45 * Construct gtod array
47 for (i = 0; i < NBUF; i ++) {
53 * Write out gtod array for later processing with Matlab
56 for (i = 0; i < NBUF - 2; i++) {
57 gtod[i] = gtod[i + 1] - gtod[i];
58 printf("%13.9f\n", gtod[i]);
63 * Sort the gtod array and display deciles
65 for (i = 0; i < NBUF - 2; i++) {
66 for (j = 0; j <= i; j++) {
67 if (gtod[j] > gtod[i]) {
74 average = average / (NBUF - 2);
75 fprintf(stderr, "Average %13.9f\n", average);
76 fprintf(stderr, "First rank\n");
77 for (i = 0; i < 10; i++)
78 fprintf(stderr, "%2d %13.9f\n", i, gtod[i]);
79 fprintf(stderr, "Last rank\n");
80 for (i = NBUF - 12; i < NBUF - 2; i++)
81 fprintf(stderr, "%2d %13.9f\n", i, gtod[i]);
87 * get_systime - return system time in NTP timestamp format.
91 l_fp *now /* system time */
96 #if defined(HAVE_CLOCK_GETTIME) || defined(HAVE_GETCLOCK)
97 struct timespec ts; /* seconds and nanoseconds */
100 * Convert Unix clock from seconds and nanoseconds to seconds.
102 # ifdef HAVE_CLOCK_GETTIME
103 clock_gettime(CLOCK_REALTIME, &ts);
105 getclock(TIMEOFDAY, &ts);
107 now->l_i = ts.tv_sec + JAN_1970;
108 dtemp = ts.tv_nsec / 1e9;
110 #else /* HAVE_CLOCK_GETTIME || HAVE_GETCLOCK */
111 struct timeval tv; /* seconds and microseconds */
114 * Convert Unix clock from seconds and microseconds to seconds.
116 gettimeofday(&tv, NULL);
117 now->l_i = tv.tv_sec + JAN_1970;
118 dtemp = tv.tv_usec / 1e6;
120 #endif /* HAVE_CLOCK_GETTIME || HAVE_GETCLOCK */
123 * Renormalize to seconds past 1900 and fraction.
125 dtemp += sys_residual;
129 } else if (dtemp < -1) {
134 now->l_uf = (u_int32)dtemp;