1/*
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.
8 */
9
10#ifdef HAVE_CONFIG_H
11# include <config.h>
12#endif
13
14#include <stdio.h>
15#include <sys/time.h>
16#include <stdlib.h>
17#include "jitter.h"
18
19#define NBUF	800002
20#define FRAC	4294967296.		/* a bbbbillion */
21#define JAN_1970 2208988800UL		/* Unix base epoch */
22#define CLOCK_GETTIME			/* Solaris hires clock */
23
24int debug;
25char progname[10];
26double sys_residual;
27double average;
28void sys_gettime(l_fp *);
29
30int
31main(
32	int argc,
33	char *argv[]
34	)
35{
36	l_fp tr;
37	int i, j;
38	double dtemp, gtod[NBUF];
39
40	/*
41	 * Force pages into memory
42	 */
43	for (i = 0; i < NBUF; i ++)
44	    gtod[i] = 0;
45
46	/*
47	 * Construct gtod array
48	 */
49	for (i = 0; i < NBUF; i ++) {
50		get_systime(&tr);
51		LFPTOD(&tr, gtod[i]);
52	}
53
54	/*
55	 * Write out gtod array for later processing with Matlab
56	 */
57	average = 0;
58	for (i = 0; i < NBUF - 2; i++) {
59		gtod[i] = gtod[i + 1] - gtod[i];
60		printf("%13.9f\n", gtod[i]);
61		average += gtod[i];
62	}
63
64	/*
65	 * Sort the gtod array and display deciles
66	 */
67	for (i = 0; i < NBUF - 2; i++) {
68		for (j = 0; j <= i; j++) {
69			if (gtod[j] > gtod[i]) {
70				dtemp = gtod[j];
71				gtod[j] = gtod[i];
72				gtod[i] = dtemp;
73			}
74		}
75	}
76	average = average / (NBUF - 2);
77	fprintf(stderr, "Average %13.9f\n", average);
78	fprintf(stderr, "First rank\n");
79	for (i = 0; i < 10; i++)
80		fprintf(stderr, "%2d %13.9f\n", i, gtod[i]);
81	fprintf(stderr, "Last rank\n");
82	for (i = NBUF - 12; i < NBUF - 2; i++)
83		fprintf(stderr, "%2d %13.9f\n", i, gtod[i]);
84	exit(0);
85}
86
87
88/*
89 * get_systime - return system time in NTP timestamp format.
90 */
91void
92get_systime(
93	l_fp *now		/* system time */
94	)
95{
96	double dtemp;
97
98#if defined(HAVE_CLOCK_GETTIME) || defined(HAVE_GETCLOCK)
99	struct timespec ts;	/* seconds and nanoseconds */
100
101	/*
102	 * Convert Unix clock from seconds and nanoseconds to seconds.
103	 */
104# ifdef HAVE_CLOCK_GETTIME
105	clock_gettime(CLOCK_REALTIME, &ts);
106# else
107	getclock(TIMEOFDAY, &ts);
108# endif
109	now->l_i = ts.tv_sec + JAN_1970;
110	dtemp = ts.tv_nsec / 1e9;
111
112#else /* HAVE_CLOCK_GETTIME || HAVE_GETCLOCK */
113	struct timeval tv;	/* seconds and microseconds */
114
115	/*
116	 * Convert Unix clock from seconds and microseconds to seconds.
117	 */
118	gettimeofday(&tv, NULL);
119	now->l_i = tv.tv_sec + JAN_1970;
120	dtemp = tv.tv_usec / 1e6;
121
122#endif /* HAVE_CLOCK_GETTIME || HAVE_GETCLOCK */
123
124	/*
125	 * Renormalize to seconds past 1900 and fraction.
126	 */
127	dtemp += sys_residual;
128	if (dtemp >= 1) {
129		dtemp -= 1;
130		now->l_i++;
131	} else if (dtemp < -1) {
132		dtemp += 1;
133		now->l_i--;
134	}
135	dtemp *= FRAC;
136	now->l_uf = (u_int32)dtemp;
137}
138