[O2-5395, EMCAL-501] Implement correct handling of events preceding timeframe

- Reject digits if it comes from a collision happening at a bc before the RO starts and the time of the digit also comes before the RO
- Time of current collision calculated w.r.t start of RO

Author: jokonig

Detectors/EMCAL/simulation/include/EMCALSimulation/Digitizer.h

@@ -110,6 +110,9 @@ class Digitizer : public TObject
   bool mSmearEnergy = true;                                                             ///< do time and energy smearing
   bool mSimulateTimeResponse = true;                                                    ///< simulate time response
   const SimParam* mSimParam = nullptr;                                                  ///< SimParam object
+  bool mIsBeforeFirstRO = false;                                                        ///< check if the signal comes before the ROF
+  o2::InteractionRecord mIRFirstSampledTF;                                              ///< IR of the 1st sampled IR, noise-only ROFs will be inserted till this IR only
+  double mTimeBCns;                                                                     ///< time difference between bc and start of ROF in ns
 
   std::vector<Digit> mTempDigitVector;     ///< temporary digit storage
   o2::emcal::DigitsWriteoutBuffer mDigits; ///< used to sort digits and labels by tower

Detectors/EMCAL/simulation/src/Digitizer.cxx

@@ -26,6 +26,8 @@
 #include "CommonDataFormat/InteractionRecord.h"
 #include "CommonUtils/TreeStreamRedirector.h"
 #include "SimConfig/DigiParams.h"
+#include "DetectorsRaw/HBFUtilsInitializer.h"
+#include "DetectorsRaw/HBFUtils.h"
 
 ClassImp(o2::emcal::Digitizer);
 
@@ -80,6 +82,8 @@ void Digitizer::init()
   } else {
   }
 
+  mIRFirstSampledTF = o2::raw::HBFUtils::Instance().getFirstSampledTFIR();
+
   if (mEnableDebugStreaming) {
     mDebugStream = std::make_unique<o2::utils::TreeStreamRedirector>("emcaldigitsDebug.root", "RECREATE");
   }
@@ -164,6 +168,13 @@ void Digitizer::sampleSDigit(const Digit& sDigit)
     return;
   }
 
+  // check if this hit because it comes from an event before readout starts and it does not effect this RO
+  LOG(debug) << "mIsBeforeFirstRO " << mIsBeforeFirstRO << "     sDigit.getTimeStamp() " << sDigit.getTimeStamp() << "    mSimParam->getSignalDelay() " << mSimParam->getSignalDelay() << "   mPhase " << mPhase << "   total: " << sDigit.getTimeStamp() + mSimParam->getSignalDelay() + mPhase * 25 << "   EMC_TOF_MAX " << EMC_TOF_MAX << "  mTimeBCns " << mTimeBCns;
+  if (mIsBeforeFirstRO && sDigit.getTimeStamp() + mTimeBCns < 0) {
+    LOG(debug) << "disregard this hit because it comes from an event before readout starts and it does not effect this RO";
+    return;
+  }
+
   Double_t energies[15];
   if (mSimulateTimeResponse) {
     if (sDigit.getTimeStamp() + mSimParam->getSignalDelay() + mPhase * 25 > EMC_TOF_MAX) {
@@ -246,4 +257,16 @@ void Digitizer::setEventTime(o2::InteractionTimeRecord record, bool trigger)
     mPhase = 0;
     mEventTimeOffset++;
   }
+
+  // get time difference between current bc and start of RO in ns
+  auto nbc = record.differenceInBC(mIRFirstSampledTF);
+  mTimeBCns = record.getTimeOffsetWrtBC();
+  mTimeBCns += nbc * o2::constants::lhc::LHCBunchSpacingNS;
+
+  if (nbc < 0) {
+    // this event is before the first RO
+    mIsBeforeFirstRO = true;
+  } else {
+    mIsBeforeFirstRO = false;
+  }
 }