From: Mike Brady <4265913+mikebrady@users.noreply.github.com>
Date: Wed, 23 Jun 2021 16:12:59 +0000 (+0100)
Subject: Handle a situation where a clock is made master without having any valid (recent... 
X-Git-Tag: 1.2~113^2~5
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=91c100121358a902ba8af54d7a37fcfb4efcdb11;p=thirdparty%2Fnqptp.git

Handle a situation where a clock is made master without having any valid (recent) samples.
---

diff --git a/nqptp-clock-sources.c b/nqptp-clock-sources.c
index ae81e27..6d47920 100644
--- a/nqptp-clock-sources.c
+++ b/nqptp-clock-sources.c
@@ -255,11 +255,20 @@ void update_master() {
         // present, definitive, sample:
 
         uint64_t oldest_acceptable_time = time_now - 10000000000; // only go back this far (ns)
+
+        int64_t cko = age_of_oldest_legitimate_sample - oldest_acceptable_time;
+        if (cko < 0)
+          debug(1,"starting sample is too old: %" PRId64 " ns.", cko);
+
         int i;
         for (i = 0; i < number_of_samples; i++) {
+
+          int64_t age = time_now - clocks_private[best_so_far].samples[i].local_time;
+
           int64_t age_relative_to_oldest_acceptable_time =
               clocks_private[best_so_far].samples[i].local_time - oldest_acceptable_time;
           if (age_relative_to_oldest_acceptable_time > 0) {
+            debug(3, "sample accepted at %f seconds old.", 0.000000001 * age);
             if (clocks_private[best_so_far].samples[i].local_time <
                 age_of_oldest_legitimate_sample) {
               age_of_oldest_legitimate_sample = clocks_private[best_so_far].samples[i].local_time;
@@ -284,27 +293,35 @@ void update_master() {
               debug(3, "sample too far into the future");
             }
           } else {
-            debug(3, "sample too old");
+            debug(3, "sample too old at %f seconds old.", 0.000000001 * age);
           }
         }
       }
 
-      clocks_private[best_so_far].mastership_start_time = age_of_oldest_legitimate_sample;
-      int64_t offset_difference =
-          best_offset_so_far - clocks_private[best_so_far].local_to_source_time_offset;
-
-      debug(2, "Lookback difference: %f ms with %d samples checked of %d samples total.",
-            0.000001 * offset_difference, samples_checked, number_of_samples);
-      clocks_private[best_so_far].local_to_source_time_offset = best_offset_so_far;
+      // it is possible that the clock has been designated master without any valid recent samples
+      // in which case the number of valid samples will be zero.
+      if (samples_checked == 0) {
+        debug(2,"clock %" PRIx64 " has become master without any recent samples...", clocks_private[best_so_far].clock_id);
+        // having no samples is a flag for the first FOLLOW_UP to set the bus mastership start time
+        // to its own reception time.
+        clocks_private[best_so_far].vacant_samples = MAX_TIMING_SAMPLES; // discard all samples
+      } else {
+        clocks_private[best_so_far].mastership_start_time = age_of_oldest_legitimate_sample;
+        int64_t offset_difference =
+            best_offset_so_far - clocks_private[best_so_far].local_to_source_time_offset;
 
-      debug(2, "Master sampling started %f ms before becoming master.",
-            0.000001 * (clocks_private[best_so_far].local_time - age_of_oldest_legitimate_sample));
-      update_master_clock_info(clocks_private[best_so_far].clock_id,
-                               (const char *)&clocks_private[best_so_far].ip,
-                               clocks_private[best_so_far].local_time,
-                               clocks_private[best_so_far].local_to_source_time_offset,
-                               clocks_private[best_so_far].mastership_start_time);
+        debug(2, "Lookback difference: %f ms with %d samples checked of %d samples total.",
+              0.000001 * offset_difference, samples_checked, number_of_samples);
+        clocks_private[best_so_far].local_to_source_time_offset = best_offset_so_far;
 
+        debug(2, "Master sampling started %f ms before becoming master.",
+              0.000001 * (clocks_private[best_so_far].local_time - age_of_oldest_legitimate_sample));
+        update_master_clock_info(clocks_private[best_so_far].clock_id,
+                                 (const char *)&clocks_private[best_so_far].ip,
+                                 clocks_private[best_so_far].local_time,
+                                 clocks_private[best_so_far].local_to_source_time_offset,
+                                 clocks_private[best_so_far].mastership_start_time);
+      }
       clocks_private[best_so_far].previous_offset_time = 0; // resync
     }
   }
diff --git a/nqptp-message-handlers.c b/nqptp-message-handlers.c
index 39ee835..da3114a 100644
--- a/nqptp-message-handlers.c
+++ b/nqptp-message-handlers.c
@@ -304,6 +304,14 @@ void handle_follow_up(char *buf, __attribute__((unused)) ssize_t recv_len,
   if (old_flags != clock_private_info->flags) {
     update_master();
   } else if ((clock_private_info->flags & (1 << clock_is_master)) != 0) {
+    // if there were no prior samples, then this must be the first sample with this clock
+    // as master. Therefore set its mastership_start_time to the reception time.
+    if (clock_private_info->vacant_samples == (MAX_TIMING_SAMPLES - 1)) {
+      debug(2,"Clock %" PRIx64 " became a bus master with no valid prior samples -- this is its first one.", clock_private_info->clock_id);
+      clock_private_info->mastership_start_time = reception_time;
+    }
+
+
     update_master_clock_info(clock_private_info->clock_id, (const char *)&clock_private_info->ip,
                              reception_time, offset, clock_private_info->mastership_start_time);
     debug(3, "clock: %" PRIx64 ", time: %" PRIu64 ", offset: %" PRId64 ", jitter: %+f ms.",