1 files changed, 136 insertions, 0 deletions
diff --git a/util/jitter.c b/util/jitter.c
new file mode 100644
index 0000000..62a84ad
--- /dev/null
+++ b/util/jitter.c
@@ -0,0 +1,136 @@
+/*
+ * 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 "jitter.h"
+
+#define NBUF	800002
+#define FRAC	4294967296.		/* a bbbbillion */
+#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;
+}