From fbad51ac199308cb69f62ccea31c1750d16fa710 Mon Sep 17 00:00:00 2001
From: Mike Brady <4265913+mikebrady@users.noreply.github.com>
Date: Mon, 10 May 2021 16:04:47 +0100
Subject: [PATCH] Check that the clock receives a positive adjustment every 10
 seconds. If not, it probably has lost sync and will be resynced.

---
 nqptp-clock-sources.h    |  7 +----
 nqptp-message-handlers.c | 57 ++++++++++++++++++++++++++--------------
 2 files changed, 38 insertions(+), 26 deletions(-)

diff --git a/nqptp-clock-sources.h b/nqptp-clock-sources.h
index 5f5f40f..6744476 100644
--- a/nqptp-clock-sources.h
+++ b/nqptp-clock-sources.h
@@ -45,13 +45,8 @@ typedef struct {
   uint64_t local_time;                  // the local time when the offset was calculated
   uint64_t local_to_source_time_offset; // add this to the local time to get source time
   uint32_t flags;
-  //  uint16_t sequence_number;
   uint16_t in_use;
-  //  uint64_t mm_count;   // mickey mouse averaging
-  //  uint64_t mm_average; // the mickey mouse average
-  //  enum stage current_stage;
-  //  uint64_t t1, t2, t3, previous_offset, previous_estimated_offset, previous_offset_time;
-  uint64_t previous_offset, previous_offset_time;
+  uint64_t previous_offset, previous_offset_time, last_sync_time;
   // for garbage collection
   uint64_t time_of_last_use; // will be taken out of use if not used for a while and not in the
                              // timing peer group
diff --git a/nqptp-message-handlers.c b/nqptp-message-handlers.c
index 261f36a..db68924 100644
--- a/nqptp-message-handlers.c
+++ b/nqptp-message-handlers.c
@@ -236,29 +236,46 @@ void handle_follow_up(char *buf, __attribute__((unused)) ssize_t recv_len,
   uint64_t offset = preciseOriginTimestamp - reception_time;
 
   int64_t jitter = 0;
-  if (clock_private_info->previous_offset != 0) {
-
-    // do acceptance checking
-    // if the new offset is greater, by any amount, than the old offset
-    // accept it
-    // if it is less than the new offset by up to what a reasonable drift divergence would allow
-    // accept it
-    // otherwise, reject it
-    // drift divergence of 1000 ppm (which is huge) would give 125 us per 125 ms.
+  if (clock_private_info->previous_offset == 0) {
+    clock_private_info->last_sync_time = reception_time;
+  } else {
 
-    jitter = offset - clock_private_info->previous_offset;
+    int64_t time_since_last_sync = reception_time - clock_private_info->last_sync_time;
+    int64_t sync_timeout = 10000000000; // nanoseconds
+    debug(2,"Sync interval: %f seconds.", 0.000000001 * time_since_last_sync);
+    if (time_since_last_sync < sync_timeout) {
+      // do acceptance checking
+      // if the new offset is greater, by any amount, than the old offset
+      // accept it
+      // if it is less than the new offset by up to what a reasonable drift divergence would allow
+      // accept it
+      // otherwise, reject it
+      // drift divergence of 1000 ppm (which is huge) would give 125 us per 125 ms.
 
-    uint64_t jitter_timing_interval = reception_time - clock_private_info->previous_offset_time;
-    long double jitterppm = 0.0;
-    if (jitter_timing_interval != 0) {
-      jitterppm = (0.001 * (jitter * 1000000000)) / jitter_timing_interval;
-      debug(2, "jitter: %" PRId64 " in: %" PRId64 " ns, %+f ppm ", jitter, jitter_timing_interval,
-            jitterppm);
-    }
+      jitter = offset - clock_private_info->previous_offset;
 
-    if (jitterppm <= -1000) {
-      jitter = -125 * 100; // i.e. 100 parts per million
-      offset = clock_private_info->previous_offset + jitter;
+      uint64_t jitter_timing_interval = reception_time - clock_private_info->previous_offset_time;
+      long double jitterppm = 0.0;
+      if (jitter_timing_interval != 0) {
+        jitterppm = (0.001 * (jitter * 1000000000)) / jitter_timing_interval;
+        debug(2, "jitter: %" PRId64 " in: %" PRId64 " ns, %+f ppm ", jitter, jitter_timing_interval,
+              jitterppm);
+      }
+      if (jitterppm >= -1000) {
+        // we take a positive or small negative jitter as a sync event
+        // as we have a new figure for the difference between the local clock and the
+        // remote clock which is almost the same or greater than our previous estimate
+        clock_private_info->last_sync_time = reception_time;
+      } else {
+        // let our previous estimate drop by some parts-per-million
+        //jitter = (-100 * jitter_timing_interval) / 1000000;
+        jitter = -10 * 1000; // this is nanoseconds in, supposedly, 125 milliseconds. 12.5 us / 125 ms is 100 ppm.
+        offset = clock_private_info->previous_offset + jitter;
+      }
+    } else {
+      debug(1,"NQPTP lost sync with clock %" PRIx64 " at %s. Resynchronising.", clock_private_info->clock_id, clock_private_info->ip);
+      // leave the offset as it was coming in and take it as a sync time
+      clock_private_info->last_sync_time = reception_time;
     }
   }
 
-- 
2.47.2