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ptp: Add median based pre-filtering of delays

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If the delay measurement is too far away from the median of the window of last
delay measurements, we discard it. This increases accuracy on wifi a lot.

https://bugzilla.gnome.org/show_bug.cgi?id=749391
This commit is contained in:
Sebastian Dröge 2015-06-03 11:04:48 +02:00
parent 02ba5b20c7
commit ac2eb6e23e
1 changed files with 63 additions and 0 deletions
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63
libs/gst/net/gstptpclock.c
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@ -106,6 +106,13 @@ GST_DEBUG_CATEGORY_STATIC (ptp_debug);
*/
#define USE_ONLY_SYNC_WITH_DELAY 1
/* Filter out delay measurements that are too far away from the median of the
* last delay measurements, currently those that are more than 2 times as big.
* This increases accuracy a lot on wifi.
*/
#define USE_MEDIAN_PRE_FILTERING 1
#define MEDIAN_PRE_FILTERING_WINDOW 9
/* How many updates should be skipped at maximum when using USE_MEASUREMENT_FILTERING */
#define MAX_SKIPPED_UPDATES 5
@ -306,6 +313,9 @@ typedef struct
GstClockTime last_delay_req, min_delay_req_interval;
guint16 last_delay_req_seqnum;
GstClockTime last_path_delays[MEDIAN_PRE_FILTERING_WINDOW];
gint last_path_delays_missing;
GQueue pending_syncs;
GstClock *domain_clock;
@ -770,6 +780,7 @@ select_best_master_clock (PtpDomainData * domain, GstClockTime now)
sizeof (PtpClockIdentity));
domain->mean_path_delay = 0;
domain->last_delay_req = 0;
domain->last_path_delays_missing = 9;
domain->min_delay_req_interval = 0;
domain->sync_interval = 0;
domain->last_ptp_sync_time = 0;
@ -834,6 +845,7 @@ handle_announce_message (PtpMessage * msg, GstClockTime receive_time)
g_object_new (GST_TYPE_SYSTEM_CLOCK, "name", clock_name, NULL);
g_free (clock_name);
g_queue_init (&domain->pending_syncs);
domain->last_path_delays_missing = 9;
domain_data = g_list_prepend (domain_data, domain);
g_mutex_lock (&domain_clocks_lock);
@ -1230,9 +1242,27 @@ out:
}
#ifdef USE_MEDIAN_PRE_FILTERING
static gint
compare_clock_time (const GstClockTime * a, const GstClockTime * b)
{
if (*a < *b)
return -1;
else if (*a > *b)
return 1;
return 0;
}
#endif
static gboolean
update_mean_path_delay (PtpDomainData * domain, PtpPendingSync * sync)
{
#ifdef USE_MEDIAN_PRE_FILTERING
GstClockTime last_path_delays[G_N_ELEMENTS (domain->last_path_delays)];
GstClockTime median;
gint i;
#endif
GstClockTime mean_path_delay, delay_req_delay;
gboolean ret;
@ -1243,6 +1273,37 @@ update_mean_path_delay (PtpDomainData * domain, PtpPendingSync * sync)
(sync->correction_field_sync + sync->correction_field_delay +
32768) / 65536) / 2;
#ifdef USE_MEDIAN_PRE_FILTERING
for (i = 1; i < G_N_ELEMENTS (domain->last_path_delays); i++)
domain->last_path_delays[i - 1] = domain->last_path_delays[i];
domain->last_path_delays[i - 1] = mean_path_delay;
if (domain->last_path_delays_missing) {
domain->last_path_delays_missing--;
} else {
memcpy (&last_path_delays, &domain->last_path_delays,
sizeof (last_path_delays));
g_qsort_with_data (&last_path_delays,
G_N_ELEMENTS (domain->last_path_delays), sizeof (GstClockTime),
(GCompareDataFunc) compare_clock_time, NULL);
median = last_path_delays[G_N_ELEMENTS (last_path_delays) / 2];
/* FIXME: We might want to use something else here, like only allowing
* things in the interquartile range, or also filtering away delays that
* are too small compared to the median. This here worked well enough
* in tests so far.
*/
if (mean_path_delay > 2 * median) {
GST_WARNING ("Path delay for domain %u too big compared to median: %"
GST_TIME_FORMAT " > 2 * %" GST_TIME_FORMAT, domain->domain,
GST_TIME_ARGS (mean_path_delay), GST_TIME_ARGS (median));
ret = FALSE;
goto out;
}
}
#endif
#ifdef USE_RUNNING_AVERAGE_DELAY
/* Track an average round trip time, for a bit of smoothing */
/* Always update before discarding a sample, so genuine changes in
@ -1344,6 +1405,7 @@ handle_sync_message (PtpMessage * msg, GstClockTime receive_time)
if (!domain) {
gchar *clock_name;
domain = g_new0 (PtpDomainData, 1);
domain->domain = msg->domain_number;
clock_name = g_strdup_printf ("ptp-clock-%u", domain->domain);
@ -1351,6 +1413,7 @@ handle_sync_message (PtpMessage * msg, GstClockTime receive_time)
g_object_new (GST_TYPE_SYSTEM_CLOCK, "name", clock_name, NULL);
g_free (clock_name);
g_queue_init (&domain->pending_syncs);
domain->last_path_delays_missing = 9;
domain_data = g_list_prepend (domain_data, domain);
g_mutex_lock (&domain_clocks_lock);