ts2phc: Use CLOCK_MONOTONIC_RAW for NMEA PPS timestamp.

In the calculation of the NMEA PPS timestamp is used an interval
measured by the CLOCK_MONOTONIC system clock. This clock may have a
large frequency error when another process (e.g. phc2sys or an NTP
client) is correcting a large time error by slewing.

This frequency error may cause the timestamp to overflow into the next
second and cause a one-second error in the measured offset, or the wrong
edge of the pulse to be rejected.

Switch from CLOCK_MONOTONIC to CLOCK_MONOTONIC_RAW to avoid the
impact of the system clock adjustments.

Signed-off-by: Miroslav Lichvar <[email protected]>

ts2phc_nmea_pps_source.c

@@ -88,7 +88,7 @@ static void *monitor_nmea_status(void *arg)
 			}
 		}
 		num = poll(&pfd, 1, NMEA_TMO);
-		clock_gettime(CLOCK_MONOTONIC, &rxtime);
+		clock_gettime(CLOCK_MONOTONIC_RAW, &rxtime);
 		clock_gettime(CLOCK_REALTIME, &rxtime_rt);
 		if (num < 0) {
 			pr_err("poll failed");
@@ -160,7 +160,7 @@ static int ts2phc_nmea_pps_source_getppstime(struct ts2phc_pps_source *src,
 	int64_t utc_time;
 	bool fix_valid;
 
-	clock_gettime(CLOCK_MONOTONIC, &now);
+	clock_gettime(CLOCK_MONOTONIC_RAW, &now);
 	local_t2 = timespec_to_tmv(now);
 
 	pthread_mutex_lock(&m->mutex);