Transceiver52M: Setup TRX mode for MS acquisition

On receipt of a SYNC command on the socket interface, set the mode to
TRX_MODE_MS_ACQUIRE, which attempts to synchronize against a remote BTS
signal by detecting the SCH burst and timing offset. The transceiver
defaults to TRX_MODE_OFF, which implies no BTS or MS capability has been
enabled.

There is currently no command to enable the BTS mode. The MS mode also
disables uplink transmission since no such capability is implemented.

Signed-off-by: Thomas Tsou <tom@tsou.cc>

Transceiver52M/Transceiver.cpp

@@ -43,7 +43,8 @@ using namespace GSM;
 #define NOISE_CNT			20
 
 TransceiverState::TransceiverState()
-  : mRetrans(false), mNoiseLev(0.0), mNoises(NOISE_CNT)
+  : mRetrans(false), mNoiseLev(0.0), mNoises(NOISE_CNT),
+    mode(Transceiver::TRX_MODE_OFF)
 {
   for (int i = 0; i < 8; i++) {
     chanType[i] = Transceiver::NONE;
@@ -194,6 +195,9 @@ void Transceiver::addRadioVector(size_t chan, BitVector &bits,
     return;
   }
 
+  if (mStates[0].mode != TRX_MODE_BTS)
+    return;
+
   burst = modulateBurst(bits, 8 + (wTime.TN() % 4 == 0), mSPSTx);
   scaleVector(*burst, txFullScale * pow(10, -RSSI / 10));
 
@@ -496,9 +500,16 @@ SoftVector *Transceiver::pullRadioVector(GSM::Time &wTime, int &RSSI,
   GSM::Time time = radio_burst->getTime();
   CorrType type = expectedCorrType(time, chan);
 
-  if ((type == OFF) || (type == IDLE)) {
-    delete radio_burst;
-    return NULL;
+  switch (state->mode) {
+  case TRX_MODE_MS_ACQUIRE:
+    type = SCH;
+    break;
+  case TRX_MODE_BTS:
+    if ((type == TSC) || (type == RACH))
+      break;
+  case TRX_MODE_OFF:
+  default:
+    goto release;
   }
 
   /* Select the diversity channel with highest energy */
@@ -513,8 +524,7 @@ SoftVector *Transceiver::pullRadioVector(GSM::Time &wTime, int &RSSI,
 
   if (max_i < 0) {
     LOG(ALERT) << "Received empty burst";
-    delete radio_burst;
-    return NULL;
+    goto release;
   }
 
   /* Average noise on diversity paths and update global levels */
@@ -525,13 +535,16 @@ SoftVector *Transceiver::pullRadioVector(GSM::Time &wTime, int &RSSI,
   /* Detect normal or RACH bursts */
   if (type == TSC)
     success = detectTSC(state, *burst, amp, toa, time);
-  else
+  else if (type == RACH)
     success = detectRACH(state, *burst, amp, toa);
+  else if (type == SCH)
+    success = detectSCH(state, *burst, amp, toa);
+  else
+    success = false;
 
   if (!success) {
     state->mNoises.insert(avg);
-    delete radio_burst;
-    return NULL;
+    goto release;
   }
 
   /* Demodulate and set output info */
@@ -548,6 +561,10 @@ SoftVector *Transceiver::pullRadioVector(GSM::Time &wTime, int &RSSI,
   delete radio_burst;
 
   return bits;
+
+release:
+  delete bits;
+  return NULL;
 }
 
 void Transceiver::start()
@@ -733,7 +750,10 @@ void Transceiver::driveControl(size_t chan)
     mStates[chan].chanType[timeslot] = (ChannelCombination) corrCode;
     setModulus(timeslot, chan);
     sprintf(response,"RSP SETSLOT 0 %d %d",timeslot,corrCode);
-
+  }
+  else if (!strcmp(command, "SYNC")) {
+    mStates[0].mode = TRX_MODE_MS_ACQUIRE;
+    sprintf(response,"RSP SYNC 0");
   }
   else {
     LOG(WARNING) << "bogus command " << command << " on control interface.";
@@ -872,7 +892,9 @@ void Transceiver::driveTxFIFO()
         }
       }
       // time to push burst to transmit FIFO
-      pushRadioVector(mTransmitDeadlineClock);
+      if (mStates[0].mode == TRX_MODE_BTS)
+        pushRadioVector(mTransmitDeadlineClock);
+
       mTransmitDeadlineClock.incTN();
     }
   }

Transceiver52M/Transceiver.h

@@ -81,6 +81,9 @@ struct TransceiverState {
   /* Received noise energy levels */
   float mNoiseLev;
   noiseVector mNoises;
+
+  /* Transceiver mode */
+  int mode;
 };
 
 /** The Transceiver class, responsible for physical layer of basestation */
@@ -231,6 +234,12 @@ public:
     LOOPBACK            ///< similar go VII, used in loopback testing
   } ChannelCombination;
 
+  enum {
+    TRX_MODE_OFF,
+    TRX_MODE_BTS,
+    TRX_MODE_MS_ACQUIRE,
+  };
+
 protected:
   /** drive lower receive I/O and burst generation */
   void driveReceiveRadio();