* This program can be used to calibrate the clock reading jitter of a

/* $NetBSD: jitter.c,v 1.6 2020/05/25 20:47:37 christos Exp $ */

/*
* This program can be used to calibrate the clock reading jitter of a
* particular CPU and operating system. It first tickles every element
* of an array, in order to force pages into memory, then repeatedly
* reads the system clock and, finally, writes out the time values for
* later analysis. From this you can determine the jitter and if the
* clock ever runs backwards.
*/

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include <stdio.h>
#include <sys/time.h>
#include <stdlib.h>
#include "ntp_fp.h"

#define NBUF 800002
#define JAN_1970 2208988800UL /* Unix base epoch */
#define CLOCK_GETTIME /* Solaris hires clock */

char progname[10];
double sys_residual;
double average;
void sys_gettime(l_fp *);

int
main(
int argc,
char *argv[]
)
{
l_fp tr;
int i, j;
double dtemp, gtod[NBUF];

/*
* Force pages into memory
*/
for (i = 0; i < NBUF; i ++)
gtod[i] = 0;

/*
* Construct gtod array
*/
for (i = 0; i < NBUF; i ++) {
get_systime(&tr);
LFPTOD(&tr, gtod[i]);
}

/*
* Write out gtod array for later processing with Matlab
*/
average = 0;
for (i = 0; i < NBUF - 2; i++) {
gtod[i] = gtod[i + 1] - gtod[i];
printf("%13.9f\n", gtod[i]);
average += gtod[i];
}

/*
* Sort the gtod array and display deciles
*/
for (i = 0; i < NBUF - 2; i++) {
for (j = 0; j <= i; j++) {
if (gtod[j] > gtod[i]) {
dtemp = gtod[j];
gtod[j] = gtod[i];
gtod[i] = dtemp;
}
}
}
average = average / (NBUF - 2);
fprintf(stderr, "Average %13.9f\n", average);
fprintf(stderr, "First rank\n");
for (i = 0; i < 10; i++)
fprintf(stderr, "%2d %13.9f\n", i, gtod[i]);
fprintf(stderr, "Last rank\n");
for (i = NBUF - 12; i < NBUF - 2; i++)
fprintf(stderr, "%2d %13.9f\n", i, gtod[i]);
exit(0);
}

/*
* get_systime - return system time in NTP timestamp format.
*/
void
get_systime(
l_fp *now /* system time */
)
{
double dtemp;

#if defined(HAVE_CLOCK_GETTIME) || defined(HAVE_GETCLOCK)
struct timespec ts; /* seconds and nanoseconds */

/*
* Convert Unix clock from seconds and nanoseconds to seconds.
*/
# ifdef HAVE_CLOCK_GETTIME
clock_gettime(CLOCK_REALTIME, &ts);
# else
getclock(TIMEOFDAY, &ts);
# endif
now->l_i = ts.tv_sec + JAN_1970;
dtemp = ts.tv_nsec / 1e9;

#else /* HAVE_CLOCK_GETTIME || HAVE_GETCLOCK */
struct timeval tv; /* seconds and microseconds */

/*
* Convert Unix clock from seconds and microseconds to seconds.
*/
gettimeofday(&tv, NULL);
now->l_i = tv.tv_sec + JAN_1970;
dtemp = tv.tv_usec / 1e6;

#endif /* HAVE_CLOCK_GETTIME || HAVE_GETCLOCK */

/*
* Renormalize to seconds past 1900 and fraction.
*/
dtemp += sys_residual;
if (dtemp >= 1) {
dtemp -= 1;
now->l_i++;
} else if (dtemp < -1) {
dtemp += 1;
now->l_i--;
}
dtemp *= FRAC;
now->l_uf = (u_int32)dtemp;
}