Gptp: fixed gmRateRatio calculation (fix for omnet discussion 1128)

old gmrateRatio calculation measured the arrival time difference of
last two arrived FollowUp packets instead of arrival time difference of
last two Sync packets.

Author: ZoltanBojthe

src/inet/linklayer/ieee8021as/Gptp.cc

@@ -376,10 +376,10 @@ void Gptp::processFollowUp(Packet *packet, const GptpFollowUp* gptp)
 void Gptp::synchronize()
 {
     simtime_t now = simTime();
-    clocktime_t origNow = clock->getClockTime();
-    clocktime_t residenceTime = origNow - syncIngressTimestamp;
+    clocktime_t oldLocalTimeAtTimeSync = clock->getClockTime();
+    clocktime_t residenceTime = oldLocalTimeAtTimeSync - syncIngressTimestamp;
 
-    emit(timeDifferenceSignal, CLOCKTIME_AS_SIMTIME(origNow) - now);
+    emit(timeDifferenceSignal, CLOCKTIME_AS_SIMTIME(oldLocalTimeAtTimeSync) - now);
 
     /************** Time synchronization *****************************************
      * Local time is adjusted using peer delay, correction field, residence time *
@@ -393,19 +393,20 @@ void Gptp::synchronize()
     if (oldPeerSentTimeSync == -1)
         gmRateRatio = 1;
     else
-        gmRateRatio = (peerSentTimeSync - oldPeerSentTimeSync) / (origNow - newLocalTimeAtTimeSync) ;
+        gmRateRatio = (peerSentTimeSync - oldPeerSentTimeSync) / (syncIngressTimestamp - receivedTimeSync);
 
     auto settableClock = check_and_cast<SettableClock *>(clock.get());
     ppm newOscillatorCompensation = unit(gmRateRatio * (1 + unit(settableClock->getOscillatorCompensation()).get()) - 1);
     settableClock->setClockTime(newTime, newOscillatorCompensation, true);
 
-    oldLocalTimeAtTimeSync = origNow;
     newLocalTimeAtTimeSync = clock->getClockTime();
+    timeDiffAtTimeSync = newLocalTimeAtTimeSync - oldLocalTimeAtTimeSync;
     receivedTimeSync = syncIngressTimestamp;
 
     // adjust local timestamps, too
-    pdelayRespEventIngressTimestamp += newLocalTimeAtTimeSync - oldLocalTimeAtTimeSync;
-    pdelayReqEventEgressTimestamp += newLocalTimeAtTimeSync - oldLocalTimeAtTimeSync;
+    adjustLocalTimestamp(pdelayRespEventIngressTimestamp);
+    adjustLocalTimestamp(pdelayReqEventEgressTimestamp);
+    adjustLocalTimestamp(receivedTimeSync);
 
     /************** Rate ratio calculation *************************************
      * It is calculated based on interval between two successive Sync messages *

src/inet/linklayer/ieee8021as/Gptp.h

@@ -56,9 +56,8 @@ class INET_API Gptp : public ClockUserModuleBase, public cListener
     clocktime_t sentTimeSyncSync;
 
     /* Slave port - Variables is used for Rate Ratio. All times are drifted based on constant drift */
-    // clocktime_t sentTimeSync;
     clocktime_t newLocalTimeAtTimeSync;
-    clocktime_t oldLocalTimeAtTimeSync;
+    clocktime_t timeDiffAtTimeSync;  // new local time - old local time
     clocktime_t peerSentTimeSync;  // sending time of last received GptpSync
     clocktime_t oldPeerSentTimeSync = -1;  // sending time of previous received GptpSync
     clocktime_t syncIngressTimestamp;  // receiving time of last incoming GptpSync
@@ -107,6 +106,7 @@ class INET_API Gptp : public ClockUserModuleBase, public cListener
 
     clocktime_t getCalculatedDrift(IClock *clock, clocktime_t value) { return CLOCKTIME_ZERO; }
     void synchronize();
+    inline void adjustLocalTimestamp(clocktime_t& time) { time += timeDiffAtTimeSync; }
 
     virtual void receiveSignal(cComponent *source, simsignal_t signal, cObject *obj, cObject *details) override;
 };