ts2phc: Allow longer NMEA delays.

Timestamps from PPS sources are rounded to the nearest pulse, i.e. for
correct synchronization the offset between the source timestamp and
external PPS event timestamp needs to be between -0.5 and +0.5 seconds.
For the pulse edge rejection to work correctly it needs to be even
smaller, between -pulsewidth/2 and +pulsewidth/2.

With the NMEA PPS source the offset is the delay in the reception of the
RMC message. This message is not expected to come exactly on time with
the corresponding pulse. A positive delay is expected, typically at
least few tens of milliseconds, but some receivers have delays longer
than 0.5 seconds.

Add NMEA-specific rounding of the offset to not expect negative delays
and allow positive delays of up to 1 second, or whole pulsewidth if the
edge rejection is enabled.

Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>

ts2phc.c

@@ -420,9 +420,16 @@ static int ts2phc_pps_source_implicit_tstamp(struct ts2phc_private *priv,
 	 * deduce the timestamp (actually only seconds part, nanoseconds are by
 	 * construction zero) of this edge at the emitter based on the
 	 * emitter's current time.
+	 *
+	 * With an NMEA source assume its messages always follow the pulse, i.e.
+	 * assign the timestamp to the previous pulse instead of nearest pulse.
 	 */
-	if (source_ts.tv_nsec > NS_PER_SEC / 2)
+	if (ts2phc_pps_source_get_type(priv->src) == TS2PHC_PPS_SOURCE_NMEA) {
 		source_ts.tv_sec++;
+	} else {
+		if (source_ts.tv_nsec > NS_PER_SEC / 2)
+			source_ts.tv_sec++;
+	}
 	source_ts.tv_nsec = 0;
 
 	tmv = timespec_to_tmv(source_ts);

ts2phc_pps_sink.c

@@ -249,8 +249,13 @@ static bool ts2phc_pps_sink_ignore(struct ts2phc_private *priv,
 	source_tmv = tmv_sub(source_tmv, priv->perout_phase);
 	source_ts = tmv_to_timespec(source_tmv);
 
-	ignore_upper = 1000000000 - sink->pulsewidth / 2;
-	ignore_lower = sink->pulsewidth / 2;
+	if (ts2phc_pps_source_get_type(priv->src) == TS2PHC_PPS_SOURCE_NMEA) {
+		ignore_upper = sink->pulsewidth;
+		ignore_lower = 0;
+	} else {
+		ignore_upper = 1000000000 - sink->pulsewidth / 2;
+		ignore_lower = sink->pulsewidth / 2;
+	}
 
 	return source_ts.tv_nsec > ignore_lower &&
 	       source_ts.tv_nsec < ignore_upper;