timedelta sensors are usually updated very often, but we used to query

them only every 30 seconds. now query them every 5,and take the median
value from 7 queries as sensor value. this takes outliers out of the
equation and makes the overall result much better, especially for
sensors with heavy jitter (like nmea for now)

src/usr.sbin/ntpd/ntp.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: ntp.c,v 1.92 2006/10/21 07:30:58 henning Exp $ */
+/*	$OpenBSD: ntp.c,v 1.93 2006/10/24 12:23:39 henning Exp $ */
 
 /*
  * Copyright (c) 2003, 2004 Henning Brauer <henning@openbsd.org>
@@ -46,7 +46,6 @@ void	ntp_sighdlr(int);
 int	ntp_dispatch_imsg(void);
 void	peer_add(struct ntp_peer *);
 void	peer_remove(struct ntp_peer *);
-int	offset_compare(const void *, const void *);
 
 void
 ntp_sighdlr(int sig)

src/usr.sbin/ntpd/ntpd.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: ntpd.h,v 1.76 2006/06/30 16:52:13 deraadt Exp $ */
+/*	$OpenBSD: ntpd.h,v 1.77 2006/10/24 12:23:39 henning Exp $ */
 
 /*
  * Copyright (c) 2003, 2004 Henning Brauer <henning@openbsd.org>
@@ -55,6 +55,7 @@
 
 #define	QUERYTIME_MAX		15	/* single query might take n secs max */
 #define	OFFSET_ARRAY_SIZE	8
+#define	SENSOR_OFFSETS		7
 #define	SETTIME_MIN_OFFSET	180	/* min offset for settime at start */
 #define	SETTIME_TIMEOUT		15	/* max seconds to wait with -s */
 #define	LOG_NEGLIGEE		32	/* negligible drift to not log (ms) */
@@ -63,7 +64,7 @@
 
 
 #define	SENSOR_DATA_MAXAGE	(15*60)
-#define	SENSOR_QUERY_INTERVAL	30
+#define	SENSOR_QUERY_INTERVAL	5
 #define	SENSOR_SCAN_INTERVAL	(5*60)
 
 enum client_state {
@@ -134,11 +135,13 @@ struct ntp_peer {
 
 struct ntp_sensor {
 	TAILQ_ENTRY(ntp_sensor)		 entry;
+	struct ntp_offset		 offsets[SENSOR_OFFSETS];
 	struct ntp_offset		 update;
 	time_t				 next;
 	char				*device;
 	int				 sensorid;
 	u_int8_t			 weight;
+	u_int8_t			 shift;
 };
 
 struct ntp_conf_sensor {
@@ -258,6 +261,7 @@ pid_t	 ntp_main(int[2], struct ntpd_conf *);
 int	 priv_adjtime(void);
 void	 priv_settime(double);
 void	 priv_host_dns(char *, u_int32_t);
+int	 offset_compare(const void *, const void *);
 
 /* parse.y */
 int	 parse_config(const char *, struct ntpd_conf *);

src/usr.sbin/ntpd/sensors.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: sensors.c,v 1.23 2006/10/12 10:41:51 henning Exp $ */
+/*	$OpenBSD: sensors.c,v 1.24 2006/10/24 12:23:39 henning Exp $ */
 
 /*
  * Copyright (c) 2006 Henning Brauer <henning@openbsd.org>
@@ -37,6 +37,7 @@
 void	sensor_probe(int);
 void	sensor_add(struct sensor *);
 void	sensor_remove(struct ntp_sensor *);
+void	sensor_update(struct ntp_sensor *);
 
 struct ntpd_conf *conf;
 
@@ -157,21 +158,54 @@ sensor_query(struct ntp_sensor *s)
 		return;
 
 	memcpy(&refid, "HARD", sizeof(refid));
-	s->update.offset = (0 - (float)sensor.value / 1000000000.0) -
+	s->offsets[s->shift].offset = (0 - (float)sensor.value / 1000000000.0) -
 	    getoffset();
-	s->update.rcvd = sensor.tv.tv_sec;
-	s->update.good = 1;
+	s->offsets[s->shift].rcvd = sensor.tv.tv_sec;
+	s->offsets[s->shift].good = 1;
+
+	s->offsets[s->shift].status.refid = htonl(refid);
+	s->offsets[s->shift].status.stratum = 0;	/* increased when sent out */
+	s->offsets[s->shift].status.rootdelay = 0;
+	s->offsets[s->shift].status.rootdispersion = 0;
+	s->offsets[s->shift].status.reftime = sensor.tv.tv_sec;
+	s->offsets[s->shift].status.synced = 1;
+
+	log_debug("sensor %s: offset %f", s->device,
+	    s->offsets[s->shift].offset);
+
+	if (++s->shift >= SENSOR_OFFSETS) {
+		s->shift = 0;
+		sensor_update(s);
+	}
 
-	s->update.status.refid = htonl(refid);
-	s->update.status.stratum = 0;	/* increased when sent out */
-	s->update.status.rootdelay = 0;
-	s->update.status.rootdispersion = 0;
-	s->update.status.reftime = sensor.tv.tv_sec;
-	s->update.status.synced = 1;
+}
 
-	priv_adjtime();
+void
+sensor_update(struct ntp_sensor *s)
+{
+	struct ntp_offset	**offsets;
+	int			  i;
+
+	if ((offsets = calloc(SENSOR_OFFSETS, sizeof(struct ntp_offset *))) ==
+	    NULL)
+		fatal("calloc sensor_update");
 
-	log_debug("sensor %s: offset %f", s->device, s->update.offset);
+	for (i = 0; i < SENSOR_OFFSETS; i++)
+		offsets[i] = &s->offsets[i];
+
+	qsort(offsets, SENSOR_OFFSETS, sizeof(struct ntp_offset *),
+	    offset_compare);
+
+	i = SENSOR_OFFSETS / 2;
+	memcpy(&s->update, offsets[i], sizeof(s->update));
+	if (SENSOR_OFFSETS % 2 == 0) {
+		s->update.offset =
+		    (offsets[i - 1]->offset + offsets[i]->offset) / 2;
+	}
+	free(offsets);
+
+	log_debug("sensor update %s: offset %f", s->device, s->update.offset);
+	priv_adjtime();
 }
 
 int