ms: Move clock indications generation to lower drive loop

During BTS operation, active downlink bursts drive the clock indication,
but the flow of bursts is not present in MS mode. Shift the indication
trigger to the lower non-blocking loop with FN mod 100 as the interval.

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

GSM/GSMCommon.cpp

@@ -45,6 +45,8 @@ const BitVector GSM::gDummyBurst("0001111101101110110000010100100111000001001000
 
 const BitVector GSM::gRACHSynchSequence("01001011011111111001100110101010001111000");
 
+const BitVector GSM::gSCHSynchSequence("1011100101100010000001000000111100101101010001010111011000011011");
+
 
 int32_t GSM::FNDelta(int32_t v1, int32_t v2)
 {

GSM/GSMCommon.h

@@ -53,6 +53,8 @@ extern const BitVector gDummyBurst;
 /** Random access burst synch. sequence */
 extern const BitVector gRACHSynchSequence;
 
+/** Synchronization burst sync sequence */
+extern const BitVector gSCHSynchSequence;
 
 /**@name Modulus operations for frame numbers. */
 //@{

Transceiver52M/Makefile.am

@@ -56,7 +56,8 @@ COMMON_SOURCES = \
 	radioClock.cpp \
 	sigProcLib.cpp \
 	signalVector.cpp \
-	Transceiver.cpp
+	Transceiver.cpp \
+	sch.c
 
 libtransceiver_la_SOURCES = \
 	$(COMMON_SOURCES) \
@@ -87,7 +88,9 @@ osmo_trx_LDADD = \
 	libtransceiver.la \
 	$(ARCH_LA) \
 	$(GSM_LA) \
-	$(COMMON_LA) $(SQLITE_LA)
+	$(COMMON_LA) \
+	$(SQLITE_LA) \
+	$(LIBOSMOCORE_LIBS)
 
 if USRP1 
 libtransceiver_la_SOURCES += USRPDevice.cpp

Transceiver52M/Transceiver.cpp

@@ -25,6 +25,10 @@
 #include "Transceiver.h"
 #include <Logger.h>
 
+extern "C" {
+#include "sch.h"
+}
+
 #ifdef HAVE_CONFIG_H
 #include "config.h"
 #endif
@@ -39,11 +43,16 @@ using namespace GSM;
 #  define USB_LATENCY_MIN		1,1
 #endif
 
+/* Clock indication interval in frames */
+#define CLK_IND_INTERVAL		100
+
 /* Number of running values use in noise average */
 #define NOISE_CNT			20
+#define FREQ_CNT			20
 
 TransceiverState::TransceiverState()
-  : mRetrans(false), mNoiseLev(0.0), mNoises(NOISE_CNT)
+  : mRetrans(false), mNoiseLev(0.0),
+    mNoises(NOISE_CNT), mFreqOffsets(FREQ_CNT), mode(Transceiver::TRX_MODE_OFF)
 {
   for (int i = 0; i < 8; i++) {
     chanType[i] = Transceiver::NONE;
@@ -51,6 +60,7 @@ TransceiverState::TransceiverState()
     chanResponse[i] = NULL;
     DFEForward[i] = NULL;
     DFEFeedback[i] = NULL;
+    prevFrame[i] = NULL;
 
     for (int n = 0; n < 102; n++)
       fillerTable[n][i] = NULL;
@@ -91,12 +101,12 @@ Transceiver::Transceiver(int wBasePort,
   : mBasePort(wBasePort), mAddr(TRXAddress),
     mTransmitLatency(wTransmitLatency), mClockSocket(NULL),
     mRadioInterface(wRadioInterface), mSPSTx(wSPS), mSPSRx(1), mChans(wChans),
-    mOn(false), mTxFreq(0.0), mRxFreq(0.0), mPower(-10), mMaxExpectedDelay(0)
+    mOn(false), mTxFreq(0.0), mRxFreq(0.0), mPower(-10), mMaxExpectedDelay(0),
+    mBSIC(-1)
 {
   GSM::Time startTime(random() % gHyperframe,0);
 
-  mRxLowerLoopThread = new Thread(32768);
+  mLowerLoopThread = new Thread(32768);
-  mTxLowerLoopThread = new Thread(32768);
 
   mTransmitDeadlineClock = startTime;
   mLastClockUpdateTime = startTime;
@@ -105,6 +115,9 @@ Transceiver::Transceiver(int wBasePort,
 
   txFullScale = mRadioInterface->fullScaleInputValue();
   rxFullScale = mRadioInterface->fullScaleOutputValue();
+
+  for (int i = 0; i < 8; i++)
+    mRxSlotMask[i] = 0;
 }
 
 Transceiver::~Transceiver()
@@ -194,6 +207,9 @@ 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));
 
@@ -221,7 +237,7 @@ void Transceiver::pushRadioVector(GSM::Time &nowTime)
   radioVector *burst;
   TransceiverState *state;
   std::vector<signalVector *> bursts(mChans);
-  std::vector<bool> zeros(mChans);
+  std::vector<bool> zeros(mChans, false);
   std::vector<bool> filler(mChans, true);
 
   for (size_t i = 0; i < mChans; i ++) {
@@ -238,7 +254,8 @@ void Transceiver::pushRadioVector(GSM::Time &nowTime)
     modFN = nowTime.FN() % state->fillerModulus[TN];
 
     bursts[i] = state->fillerTable[modFN][TN];
-    zeros[i] = state->chanType[TN] == NONE;
+    if (state->mode == TRX_MODE_BTS)
+      zeros[i] = state->chanType[TN] == NONE;
 
     if ((burst = mTxPriorityQueues[i].getCurrentBurst(nowTime))) {
       bursts[i] = burst->getVector();
@@ -299,6 +316,19 @@ Transceiver::CorrType Transceiver::expectedCorrType(GSM::Time currTime,
   unsigned burstTN = currTime.TN();
   unsigned burstFN = currTime.FN();
 
+  if (state->mode == TRX_MODE_MS_TRACK) {
+    /* 102 modulus case currently unhandled */
+    if (state->fillerModulus[burstTN] > 52)
+      return OFF;
+
+    int modFN = burstFN % state->fillerModulus[burstTN];
+    unsigned long long reg = (unsigned long long) 1 << modFN;
+    if (reg & mRxSlotMask[burstTN])
+      return TSC;
+    else
+      return OFF;
+  }
+
   switch (state->chanType[burstTN]) {
   case NONE:
     return OFF;
@@ -376,6 +406,108 @@ bool Transceiver::detectRACH(TransceiverState *state,
   return detectRACHBurst(burst, threshold, mSPSRx, &amp, &toa);
 }
 
+/* Detect SCH synchronization sequence within a burst */
+bool Transceiver::detectSCH(TransceiverState *state,
+                            signalVector &burst,
+                            complex &amp, float &toa)
+{
+  int shift, full;;
+  float mag, threshold = 7.0;
+
+  full = (state->mode == TRX_MODE_MS_TRACK) ?
+	 SCH_DETECT_NARROW : SCH_DETECT_FULL;
+
+  if (!detectSCHBurst(burst, threshold, mSPSRx, &amp, &toa, full))
+    return false;
+
+  std::cout << "SCH : Timing offset     " << toa << " symbols" << std::endl;
+
+  mag = fabsf(toa);
+  if (mag < 1.0f)
+    return true;
+
+  shift = (int) (mag / 2.0f);
+  if (!shift)
+    shift++;
+
+  mRadioInterface->applyOffset(toa > 0 ? shift : -shift);
+  return false;
+}
+
+#define SCH_BIT_SCALE	64
+
+/* Decode SCH burst */
+bool Transceiver::decodeSCH(SoftVector *burst, GSM::Time *time)
+{
+  int fn;
+  struct sch_info sch;
+  ubit_t info[GSM_SCH_INFO_LEN];
+  sbit_t data[GSM_SCH_CODED_LEN];
+
+  if (burst->size() < 156) {
+    std::cout << "Invalid SCH burst length" << std::endl;
+    return false;
+  }
+
+  float_to_sbit(&(*burst)[3], &data[0], SCH_BIT_SCALE, 39);
+  float_to_sbit(&(*burst)[106], &data[39], SCH_BIT_SCALE, 39);
+
+  if (!gsm_sch_decode(info, data)) {
+    gsm_sch_parse(info, &sch);
+
+    mBSIC = sch.bsic;
+
+    std::cout << "SCH : Decoded values" << std::endl;
+    std::cout << "    BSIC: " << sch.bsic << std::endl;
+    std::cout << "    T1  : " << sch.t1 << std::endl;
+    std::cout << "    T2  : " << sch.t2 << std::endl;
+    std::cout << "    T3p : " << sch.t3p << std::endl;
+    std::cout << "    FN  : " << gsm_sch_to_fn(&sch) << std::endl;
+
+    fn = gsm_sch_to_fn(&sch);
+    if (fn < 0) {
+      std::cout << "SCH : Failed to convert FN " << std::endl;
+      return false;
+    }
+
+    time->FN(fn);
+    time->TN(0);
+  } else {
+    return false;
+  }
+
+  return true;
+}
+
+#define FCCH_OFFSET_LIMIT	2e3
+#define FCCH_ADJUST_LIMIT	20.0
+
+/* Apply FCCH frequency correction */
+bool Transceiver::correctFCCH(TransceiverState *state, signalVector *burst)
+{
+  double offset, avg;
+
+  if (!burst)
+    return false;
+
+  offset = gsm_fcch_offset((float *) burst->begin(), burst->size());
+  if (offset > FCCH_OFFSET_LIMIT)
+    return false;
+
+  state->mFreqOffsets.insert(offset);
+  avg = state->mFreqOffsets.avg();
+
+  if (state->mFreqOffsets.full())
+    std::cout << "FCCH: Frequency offset  " << avg << " Hz" << std::endl;
+
+  if (state->mFreqOffsets.full() && (fabs(avg) > FCCH_ADJUST_LIMIT)) {
+    mRadioInterface->tuneRxOffset(-avg);
+    state->mFreqOffsets.reset();
+  }
+
+  return true;
+}
+
 /*
  * Detect normal burst training sequence midamble. Update equalization
  * state information and channel estimate if necessary. Equalization
@@ -462,18 +594,33 @@ SoftVector *Transceiver::pullRadioVector(GSM::Time &wTime, int &RSSI,
   SoftVector *bits = NULL;
   TransceiverState *state = &mStates[chan];
 
+  GSM::Time sch_time, burst_time, diff_time;
+
   /* Blocking FIFO read */
   radioVector *radio_burst = mReceiveFIFO[chan]->read();
   if (!radio_burst)
     return NULL;
 
   /* Set time and determine correlation type */
-  GSM::Time time = radio_burst->getTime();
+  burst_time = radio_burst->getTime();
-  CorrType type = expectedCorrType(time, chan);
+  CorrType type = expectedCorrType(burst_time, chan);
 
-  if ((type == OFF) || (type == IDLE)) {
+  switch (state->mode) {
-    delete radio_burst;
+  case TRX_MODE_MS_ACQUIRE:
-    return NULL;
+    type = SCH;
+    break;
+  case TRX_MODE_MS_TRACK:
+    if (gsm_sch_check_fn(burst_time.FN()))
+      type = SCH;
+    else if (type == OFF)
+      goto release; 
+    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 */
@@ -488,8 +635,7 @@ SoftVector *Transceiver::pullRadioVector(GSM::Time &wTime, int &RSSI,
 
   if (max_i < 0) {
     LOG(ALERT) << "Received empty burst";
-    delete radio_burst;
+    goto release;
-    return NULL;
   }
 
   /* Average noise on diversity paths and update global levels */
@@ -499,30 +645,66 @@ SoftVector *Transceiver::pullRadioVector(GSM::Time &wTime, int &RSSI,
 
   /* Detect normal or RACH bursts */
   if (type == TSC)
-    success = detectTSC(state, *burst, amp, toa, time);
+    success = detectTSC(state, *burst, amp, toa, burst_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;
+    goto release;
-    return NULL;
   }
 
   /* Demodulate and set output info */
   if (equalize && (type != TSC))
     equalize = false;
 
-  if (avg - state->mNoiseLev > 0.0)
+  /* Ignore noise threshold on MS mode for now */
-    bits = demodulate(state, *burst, amp, toa, time.TN(), equalize);
+  if ((type == SCH) || (avg - state->mNoiseLev > 0.0))
+    bits = demodulate(state, *burst, amp, toa,
+		      burst_time.TN(), equalize);
 
-  wTime = time;
+  /* MS: Decode SCH and adjust GSM clock */
+  if ((state->mode == TRX_MODE_MS_ACQUIRE) ||
+      (state->mode == TRX_MODE_MS_TRACK)) {
+    correctFCCH(state, state->prevFrame[burst_time.TN()]->getVector());
+
+    if (decodeSCH(bits, &sch_time)) {
+      if (state->mode == TRX_MODE_MS_ACQUIRE) {
+          diff_time = GSM::Time(sch_time.FN() - burst_time.FN(),
+                                -burst_time.TN());
+          mRadioInterface->adjustClock(diff_time);
+          mTransmitDeadlineClock = RadioClock::adjust(
+					mTransmitDeadlineClock,
+					diff_time);
+          state->mode = TRX_MODE_MS_TRACK;
+
+          std::cout << "SCH : Locking GSM clock " << std::endl;
+      } else {
+        std::cout << "SCH : Read SCH at FN " << burst_time.FN()
+                  << " FN51 " << burst_time.FN() % 51 << std::endl;
+      }
+    }
+    goto release;
+  }
+
+  wTime = burst_time;
   RSSI = (int) floor(20.0 * log10(rxFullScale / avg));
   timingOffset = (int) round(toa * 256.0 / mSPSRx);
 
-  delete radio_burst;
+  delete state->prevFrame[burst_time.TN()];
+  state->prevFrame[burst_time.TN()] = radio_burst;
 
   return bits;
+
+release:
+  delete state->prevFrame[burst_time.TN()];
+  state->prevFrame[burst_time.TN()] = radio_burst;
+  delete bits;
+  return NULL;
 }
 
 void Transceiver::start()
@@ -589,10 +771,8 @@ void Transceiver::driveControl(size_t chan)
         mRadioInterface->start();
 
         // Start radio interface threads.
-        mTxLowerLoopThread->start((void * (*)(void*))
+        mLowerLoopThread->start((void * (*)(void*))
-                                  TxLowerLoopAdapter,(void*) this);
+                                LowerLoopAdapter,(void*) this);
-        mRxLowerLoopThread->start((void * (*)(void*))
-                                  RxLowerLoopAdapter,(void*) this);
 
         for (size_t i = 0; i < mChans; i++) {
           TransceiverChannel *chan = new TransceiverChannel(this, i);
@@ -695,6 +875,12 @@ void Transceiver::driveControl(size_t chan)
       sprintf(response,"RSP SETTSC 0 %d", TSC);
     }
   }
+  else if (!strcmp(command,"GETBSIC")) {
+    if (mBSIC < 0)
+      sprintf(response, "RSP GETBSIC 1");
+    else
+      sprintf(response, "RSP GETBSIC 0 %d", mBSIC);
+  }
   else if (strcmp(command,"SETSLOT")==0) {
     // set TSC 
     int  corrCode;
@@ -708,7 +894,21 @@ 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,"SETRXMASK")) {
+    int slot;
+    unsigned long long mask;
+    sscanf(buffer,"%3s %s %d 0x%llx", cmdcheck, command, &slot, &mask);
+    if ((slot < 0) || (slot > 7)) {
+      sprintf(response, "RSP SETRXMASK 1");
+    } else {
+      mRxSlotMask[slot] = mask;
+      sprintf(response, "RSP SETRXMASK 0 %d 0x%llx", slot, mask);
+    }
+  }
+  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.";
@@ -734,15 +934,6 @@ bool Transceiver::driveTxPriorityQueue(size_t chan)
   for (int i = 0; i < 4; i++)
     frameNum = (frameNum << 8) | (0x0ff & buffer[i+1]);
 
-  // periodically update GSM core clock
-  LOG(DEBUG) << "mTransmitDeadlineClock " << mTransmitDeadlineClock
-		<< " mLastClockUpdateTime " << mLastClockUpdateTime;
-
-  if (!chan) {
-    if (mTransmitDeadlineClock > mLastClockUpdateTime + GSM::Time(216,0))
-      writeClockInterface();
-  }
-
   LOG(DEBUG) << "rcvd. burst at: " << GSM::Time(frameNum,timeSlot);
   
   int RSSI = (int) buffer[5];
@@ -848,7 +1039,13 @@ void Transceiver::driveTxFIFO()
       }
       // time to push burst to transmit FIFO
       pushRadioVector(mTransmitDeadlineClock);
+
       mTransmitDeadlineClock.incTN();
+
+      if (!mTransmitDeadlineClock.TN() &&
+          !(mTransmitDeadlineClock.FN() % CLK_IND_INTERVAL)) {
+        writeClockInterface();
+      }
     }
   }
 
@@ -887,22 +1084,12 @@ void *RxUpperLoopAdapter(TransceiverChannel *chan)
   return NULL;
 }
 
-void *RxLowerLoopAdapter(Transceiver *transceiver)
+void *LowerLoopAdapter(Transceiver *transceiver)
 {
   transceiver->setPriority(0.45);
 
   while (1) {
     transceiver->driveReceiveRadio();
-    pthread_testcancel();
-  }
-  return NULL;
-}
-
-void *TxLowerLoopAdapter(Transceiver *transceiver)
-{
-  transceiver->setPriority(0.44);
-
-  while (1) {
     transceiver->driveTxFIFO();
     pthread_testcancel();
   }

Transceiver52M/Transceiver.h

@@ -80,7 +80,14 @@ struct TransceiverState {
 
   /* Received noise energy levels */
   float mNoiseLev;
-  noiseVector mNoises;
+  avgVector mNoises;
+  avgVector mFreqOffsets;
+
+  /* Store pointers to previous frame */
+  radioVector *prevFrame[8];
+
+  /* Transceiver mode */
+  int mode;
 };
 
 /** The Transceiver class, responsible for physical layer of basestation */
@@ -99,8 +106,7 @@ private:
   std::vector<VectorFIFO *>  mReceiveFIFO;      ///< radioInterface FIFO of receive bursts
 
   std::vector<Thread *> mRxServiceLoopThreads;  ///< thread to pull bursts into receive FIFO
-  Thread *mRxLowerLoopThread;                   ///< thread to pull bursts into receive FIFO
+  Thread *mLowerLoopThread;                   ///< thread to pull bursts into receive FIFO
-  Thread *mTxLowerLoopThread;                   ///< thread to push bursts into transmit FIFO
   std::vector<Thread *> mControlServiceLoopThreads;         ///< thread to process control messages from GSM core
   std::vector<Thread *> mTxPriorityQueueServiceLoopThreads; ///< thread to process transmit bursts from GSM core
 
@@ -116,6 +122,7 @@ private:
     OFF,               ///< timeslot is off
     TSC,	       ///< timeslot should contain a normal burst
     RACH,	       ///< timeslot should contain an access burst
+    SCH,	       ///< timeslot should contain a SCH burst
     IDLE	       ///< timeslot is an idle (or dummy) burst
   } CorrType;
 
@@ -147,6 +154,13 @@ private:
                   signalVector &burst,
                   complex &amp, float &toa);
 
+  bool detectSCH(TransceiverState *state,
+                  signalVector &burst,
+                  complex &amp, float &toa);
+
+  bool decodeSCH(SoftVector *burst, GSM::Time *time);
+  bool correctFCCH(TransceiverState *state, signalVector *burst);
+
   /** Detect normal bursts */
   bool detectTSC(TransceiverState *state,
                  signalVector &burst,
@@ -167,7 +181,9 @@ private:
   double mRxFreq;                      ///< the receive frequency
   int mPower;                          ///< the transmit power in dB
   unsigned mTSC;                       ///< the midamble sequence code
-  unsigned mMaxExpectedDelay;            ///< maximum expected time-of-arrival offset in GSM symbols
+  unsigned mMaxExpectedDelay;          ///< maximum TOA offset in GSM symbols
+  unsigned long long mRxSlotMask[8];   ///< MS - enabled multiframe slot mask
+  int mBSIC;                           ///< MS - detected BSIC
 
   std::vector<TransceiverState> mStates;
 
@@ -226,6 +242,13 @@ public:
     LOOPBACK            ///< similar go VII, used in loopback testing
   } ChannelCombination;
 
+  enum {
+    TRX_MODE_OFF,
+    TRX_MODE_BTS,
+    TRX_MODE_MS_ACQUIRE,
+    TRX_MODE_MS_TRACK,
+  };
+
 protected:
   /** drive lower receive I/O and burst generation */
   void driveReceiveRadio();
@@ -249,9 +272,7 @@ protected:
 
   friend void *TxUpperLoopAdapter(TransceiverChannel *);
 
-  friend void *RxLowerLoopAdapter(Transceiver *);
+  friend void *LowerLoopAdapter(Transceiver *);
-
-  friend void *TxLowerLoopAdapter(Transceiver *);
 
   friend void *ControlServiceLoopAdapter(TransceiverChannel *);
 
@@ -266,8 +287,7 @@ protected:
 void *RxUpperLoopAdapter(TransceiverChannel *);
 
 /** Main drive threads */
-void *RxLowerLoopAdapter(Transceiver *);
+void *LowerLoopAdapter(Transceiver *);
-void *TxLowerLoopAdapter(Transceiver *);
 
 /** control message handler thread loop */
 void *ControlServiceLoopAdapter(TransceiverChannel *);

Transceiver52M/UHDDevice.cpp

@@ -58,6 +58,11 @@ struct uhd_dev_offset {
 	const std::string desc;
 };
 
+struct tune_result {
+	uhd::tune_result_t uhd;
+	double freq;
+};
+
 /*
  * Tx / Rx sample offset values. In a perfect world, there is no group delay
  * though analog components, and behaviour through digital filters exactly
@@ -282,6 +287,7 @@ public:
 
 	bool setTxFreq(double wFreq, size_t chan);
 	bool setRxFreq(double wFreq, size_t chan);
+	bool setRxOffset(double wOffset, size_t chan);
 
 	inline TIMESTAMP initialWriteTimestamp() { return ts_initial * sps; }
 	inline TIMESTAMP initialReadTimestamp() { return ts_initial; }
@@ -332,7 +338,7 @@ private:
 	double offset;
 
 	std::vector<double> tx_gains, rx_gains;
-	std::vector<double> tx_freqs, rx_freqs;
+	std::vector<tune_result> tx_freqs, rx_freqs;
 	size_t tx_spp, rx_spp;
 
 	bool started;
@@ -886,7 +892,7 @@ int uhd_device::readSamples(std::vector<short *> &bufs, int len, bool *overrun,
 	if (rc < 0) {
 		LOG(ERR) << rx_buffers[0]->str_code(rc);
 		LOG(ERR) << rx_buffers[0]->str_status();
-		return 0;
+		return len;
 	}
 
 	// Create vector buffer
@@ -996,15 +1002,17 @@ int uhd_device::writeSamples(std::vector<short *> &bufs, int len, bool *underrun
 	return num_smpls;
 }
 
-bool uhd_device::updateAlignment(TIMESTAMP timestamp)
+bool uhd_device::updateAlignment(TIMESTAMP)
 {
+	aligned = false;
+
 	return true;
 }
 
 uhd::tune_request_t uhd_device::select_freq(double freq, size_t chan, bool tx)
 {
 	double rf_spread, rf_freq;
-	std::vector<double> freqs;
+	std::vector<tune_result> freqs;
 	uhd::tune_request_t treq(freq);
 
 	if ((chans == 1) || ((chans == 2) && dev_type == UMTRX)) {
@@ -1023,17 +1031,17 @@ uhd::tune_request_t uhd_device::select_freq(double freq, size_t chan, bool tx)
 		freqs = rx_freqs;
 
 	/* Tune directly if other channel isn't tuned */
-	if (freqs[!chan] < 10.0)
+	if (freqs[!chan].freq < 10.0)
 		return treq;
 
 	/* Find center frequency between channels */
-	rf_spread = fabs(freqs[!chan] - freq);
+	rf_spread = fabs(freqs[!chan].freq - freq);
 	if (rf_spread > B2XX_CLK_RT) {
 		LOG(ALERT) << rf_spread << "Hz tuning spread not supported\n";
 		return treq;
 	}
 
-	rf_freq = (freqs[!chan] + freq) / 2.0f;
+	rf_freq = (freqs[!chan].freq + freq) / 2.0f;
 
 	treq.rf_freq_policy = uhd::tune_request_t::POLICY_MANUAL;
 	treq.target_freq = freq;
@@ -1050,10 +1058,12 @@ bool uhd_device::set_freq(double freq, size_t chan, bool tx)
 
 	if (tx) {
 		tres = usrp_dev->set_tx_freq(treq, chan);
-		tx_freqs[chan] = usrp_dev->get_tx_freq(chan);
+		tx_freqs[chan].uhd = tres;
+		tx_freqs[chan].freq = usrp_dev->get_tx_freq(chan);
 	} else {
 		tres = usrp_dev->set_rx_freq(treq, chan);
-		rx_freqs[chan] = usrp_dev->get_rx_freq(chan);
+		rx_freqs[chan].uhd = tres;
+		rx_freqs[chan].freq = usrp_dev->get_rx_freq(chan);
 	}
 	LOG(INFO) << "\n" << tres.to_pp_string() << std::endl;
 
@@ -1066,13 +1076,15 @@ bool uhd_device::set_freq(double freq, size_t chan, bool tx)
 	 */
 	if (treq.rf_freq_policy == uhd::tune_request_t::POLICY_MANUAL) {
 		if (tx) {
-			treq = select_freq(tx_freqs[!chan], !chan, true);
+			treq = select_freq(tx_freqs[!chan].freq, !chan, true);
 			tres = usrp_dev->set_tx_freq(treq, !chan);
-			tx_freqs[!chan] = usrp_dev->get_tx_freq(!chan);
+			tx_freqs[!chan].uhd = tres;
+			tx_freqs[!chan].freq = usrp_dev->get_tx_freq(!chan);
 		} else {
-			treq = select_freq(rx_freqs[!chan], !chan, false);
+			treq = select_freq(rx_freqs[!chan].freq, !chan, false);
 			tres = usrp_dev->set_rx_freq(treq, !chan);
-			rx_freqs[!chan] = usrp_dev->get_rx_freq(!chan);
+			rx_freqs[!chan].uhd = tres;
+			rx_freqs[!chan].freq = usrp_dev->get_rx_freq(!chan);
 
 		}
 		LOG(INFO) << "\n" << tres.to_pp_string() << std::endl;
@@ -1091,6 +1103,20 @@ bool uhd_device::setTxFreq(double wFreq, size_t chan)
 	return set_freq(wFreq, chan, true);
 }
 
+bool uhd_device::setRxOffset(double wOffset, size_t chan)
+{
+	uhd::tune_result_t tres;
+	uhd::tune_request_t treq(rx_freqs[chan].freq - wOffset);
+
+	treq.rf_freq_policy = uhd::tune_request_t::POLICY_MANUAL;
+	treq.rf_freq = rx_freqs[chan].uhd.actual_rf_freq;
+
+	tres = usrp_dev->set_rx_freq(treq, chan);
+	rx_freqs[chan].freq = usrp_dev->get_rx_freq(chan);
+
+	return true;
+}
+
 bool uhd_device::setRxFreq(double wFreq, size_t chan)
 {
 	if (chan >= rx_freqs.size()) {
@@ -1108,7 +1134,7 @@ double uhd_device::getTxFreq(size_t chan)
 		return 0.0;
 	}
 
-	return tx_freqs[chan];
+	return tx_freqs[chan].freq;
 }
 
 double uhd_device::getRxFreq(size_t chan)
@@ -1118,7 +1144,7 @@ double uhd_device::getRxFreq(size_t chan)
 		return 0.0;
 	}
 
-	return rx_freqs[chan];
+	return rx_freqs[chan].freq;
 }
 
 bool uhd_device::recv_async_msg()

Transceiver52M/osmo-trx.cpp

@@ -68,6 +68,7 @@ struct trx_config {
 	bool extref;
 	bool filler;
 	bool diversity;
+	bool ms;
 	double offset;
 };
 
@@ -118,7 +119,7 @@ bool testConfig()
  */
 bool trx_setup_config(struct trx_config *config)
 {
-	std::string refstr, fillstr, divstr;
+	std::string refstr, fillstr, divstr, msstr;
 
 	if (!testConfig())
 		return false;
@@ -167,6 +168,7 @@ bool trx_setup_config(struct trx_config *config)
 	refstr = config->extref ? "Enabled" : "Disabled";
 	fillstr = config->filler ? "Enabled" : "Disabled";
 	divstr = config->diversity ? "Enabled" : "Disabled";
+	msstr = config->ms ? "Enabled" : "Disabled";
 
 	std::ostringstream ost("");
 	ost << "Config Settings" << std::endl;
@@ -179,6 +181,7 @@ bool trx_setup_config(struct trx_config *config)
 	ost << "   External Reference...... " << refstr << std::endl;
 	ost << "   C0 Filler Table......... " << fillstr << std::endl;
 	ost << "   Diversity............... " << divstr << std::endl;
+	ost << "   MS Mode................. " << msstr << std::endl;
 	ost << "   Tuning offset........... " << config->offset << std::endl;
 	std::cout << ost << std::endl;
 
@@ -196,10 +199,22 @@ RadioInterface *makeRadioInterface(struct trx_config *config,
                                    RadioDevice *usrp, int type)
 {
 	RadioInterface *radio = NULL;
+	size_t div = 1;
+	int offset = 3;
+
+	if (config->ms) {
+		if (type != RadioDevice::NORMAL) {
+			LOG(ALERT) << "Unsupported configuration";
+			return NULL;
+		}
+
+		offset *= -1;
+	}
 
 	switch (type) {
 	case RadioDevice::NORMAL:
-		radio = new RadioInterface(usrp, config->sps, config->chans);
+		radio = new RadioInterface(usrp, config->sps,
+					   config->chans, div, offset);
 		break;
 	case RadioDevice::RESAMP_64M:
 	case RadioDevice::RESAMP_100M:
@@ -286,6 +301,7 @@ static void print_help()
 		"  -s    Samples-per-symbol (1 or 4)\n"
 		"  -c    Number of ARFCN channels (default=1)\n"
 		"  -f    Enable C0 filler table\n"
+		"  -m    Enable MS mode\n"
 		"  -o    Set baseband frequency offset (default=auto)\n",
 		"EMERG, ALERT, CRT, ERR, WARNING, NOTICE, INFO, DEBUG");
 }
@@ -300,9 +316,10 @@ static void handle_options(int argc, char **argv, struct trx_config *config)
 	config->extref = false;
 	config->filler = false;
 	config->diversity = false;
+	config->ms = false;
 	config->offset = 0.0;
 
-	while ((option = getopt(argc, argv, "ha:l:i:p:c:dxfo:s:")) != -1) {
+	while ((option = getopt(argc, argv, "ha:l:i:p:c:dxfo:ms:")) != -1) {
 		switch (option) {
 		case 'h':
 			print_help();
@@ -335,6 +352,9 @@ static void handle_options(int argc, char **argv, struct trx_config *config)
 		case 'o':
 			config->offset = atof(optarg);
 			break;
+		case 'm':
+			config->ms = true;
+			break;
 		case 's':
 			config->sps = atoi(optarg);
 			if ((config->sps != 1) && (config->sps != 4)) {

Transceiver52M/radioClock.cpp

@@ -29,6 +29,40 @@ void RadioClock::set(const GSM::Time& wTime)
 	mLock.unlock();
 }
 
+GSM::Time RadioClock::adjust(GSM::Time &wBase, GSM::Time &wOffset)
+{
+	int tn_diff, fn_diff = 0;
+
+	/* Modulo TN adustment */
+	tn_diff = wBase.TN() + wOffset.TN();
+	if (tn_diff < 0) {
+		tn_diff += 8;
+		fn_diff--;
+	} else if (tn_diff >= 8) {
+		tn_diff -= 8;
+		fn_diff++;
+	}
+
+	/* Modulo FN adjustment */
+	fn_diff += wBase.FN() + wOffset.FN();
+	if (fn_diff < 0)
+		fn_diff += GSM::gHyperframe;
+	else if ((unsigned) fn_diff >= GSM::gHyperframe)
+		fn_diff = fn_diff - GSM::gHyperframe;
+
+	return GSM::Time(fn_diff, tn_diff);
+}
+
+void RadioClock::adjust(GSM::Time& wOffset)
+{
+	mLock.lock();
+
+	mClock = adjust(mClock, wOffset); 
+	updateSignal.signal();
+
+	mLock.unlock();
+}
+
 void RadioClock::incTN()
 {
 	mLock.lock();

Transceiver52M/radioClock.h

@@ -26,7 +26,10 @@
 
 class RadioClock {
 public:
+	static GSM::Time adjust(GSM::Time &base, GSM::Time &offset);
+
 	void set(const GSM::Time& wTime);
+	void adjust(GSM::Time &wOffset);
 	void incTN();
 	GSM::Time get();
 	void wait();

Transceiver52M/radioDevice.h

@@ -91,6 +91,9 @@ class RadioDevice {
   /** Set the receiver frequency */
   virtual bool setRxFreq(double wFreq, size_t chan = 0) = 0;
 
+  /** Adjust the receiver offset */
+  virtual bool setRxOffset(double wOffset, size_t chan = 0) = 0;
+
   /** Returns the starting write Timestamp*/
   virtual TIMESTAMP initialWriteTimestamp(void)=0;
 

Transceiver52M/radioInterface.cpp

@@ -38,7 +38,8 @@ RadioInterface::RadioInterface(RadioDevice *wRadio,
                                int wReceiveOffset, GSM::Time wStartTime)
   : mRadio(wRadio), mSPSTx(sps), mSPSRx(1), mChans(chans), mMIMO(diversity),
     sendCursor(0), recvCursor(0), underrun(false), overrun(false),
-    receiveOffset(wReceiveOffset), mOn(false)
+    receiveOffset(wReceiveOffset), shiftOffset(0), shiftUpdate(false),
+    mOn(false)
 {
   mClock.set(wStartTime);
 }
@@ -157,6 +158,11 @@ int RadioInterface::unRadioifyVector(float *floatVector,
   return newVector.size();
 }
 
+void RadioInterface::adjustClock(GSM::Time &offset)
+{
+  mClock.adjust(offset);
+}
+
 bool RadioInterface::tuneTx(double freq, size_t chan)
 {
   return mRadio->setTxFreq(freq, chan);
@@ -167,6 +173,10 @@ bool RadioInterface::tuneRx(double freq, size_t chan)
   return mRadio->setRxFreq(freq, chan);
 }
 
+bool RadioInterface::tuneRxOffset(double offset, size_t chan)
+{
+  return mRadio->setRxOffset(offset, chan);
+}
 
 void RadioInterface::start()
 {
@@ -228,7 +238,11 @@ bool RadioInterface::driveReceiveRadio()
   pullBuffer();
 
   GSM::Time rcvClock = mClock.get();
-  rcvClock.decTN(receiveOffset);
+  if (receiveOffset < 0)
+    rcvClock.incTN(-receiveOffset);
+  else
+    rcvClock.decTN(receiveOffset);
+
   unsigned tN = rcvClock.TN();
   int recvSz = recvCursor;
   int readSz = 0;
@@ -292,6 +306,12 @@ bool RadioInterface::isUnderrun()
   return retVal;
 }
 
+void RadioInterface::applyOffset(int offset)
+{
+  shiftOffset += offset;
+  shiftUpdate = true;
+}
+
 VectorFIFO* RadioInterface::receiveFIFO(size_t chan)
 {
   if (chan >= mReceiveFIFO.size())
@@ -330,7 +350,7 @@ void RadioInterface::pullBuffer()
   num_recv = mRadio->readSamples(convertRecvBuffer,
                                  CHUNK,
                                  &overrun,
-                                 readTimestamp,
+                                 readTimestamp + shiftOffset,
                                  &local_underrun);
   if (num_recv != CHUNK) {
           LOG(ALERT) << "Receive error " << num_recv;
@@ -365,11 +385,16 @@ void RadioInterface::pushBuffer()
                         powerScaling[i], 2 * sendCursor);
   }
 
+  if (shiftUpdate) {
+    mRadio->updateAlignment(0);
+    shiftUpdate = false;
+  }
+
   /* Send the all samples in the send buffer */ 
   num_sent = mRadio->writeSamples(convertSendBuffer,
                                   sendCursor,
                                   &underrun,
-                                  writeTimestamp);
+                                  writeTimestamp + mSPSTx * shiftOffset);
   writeTimestamp += num_sent;
   sendCursor = 0;
 }

Transceiver52M/radioInterface.h

@@ -56,7 +56,8 @@ protected:
   RadioClock mClock;                          ///< the basestation clock!
 
   int receiveOffset;                          ///< offset b/w transmit and receive GSM timestamps, in timeslots
-
+  int shiftOffset;
+  bool shiftUpdate;
   bool mOn;				      ///< indicates radio is on
 
 private:
@@ -94,6 +95,7 @@ public:
 
   /** check for underrun, resets underrun value */
   bool isUnderrun();
+  void applyOffset(int offset);
 
   /** return the receive FIFO */
   VectorFIFO* receiveFIFO(size_t chan = 0);
@@ -101,12 +103,18 @@ public:
   /** return the basestation clock */
   RadioClock* getClock(void) { return &mClock;};
 
+  /** apply an offset to the main clock */
+  void adjustClock(GSM::Time &offset);
+
   /** set transmit frequency */
   bool tuneTx(double freq, size_t chan = 0);
 
   /** set receive frequency */
   virtual bool tuneRx(double freq, size_t chan = 0);
 
+  /** set frequency correction */
+  virtual bool tuneRxOffset(double offset, size_t chan = 0);
+
   /** set receive gain */
   double setRxGain(double dB, size_t chan = 0);
 

Transceiver52M/radioInterfaceDiversity.cpp

@@ -189,7 +189,7 @@ void RadioInterfaceDiversity::pullBuffer()
 	num = mRadio->readSamples(convertRecvBuffer,
 				  resamp_outchunk,
 				  &overrun,
-				  readTimestamp,
+				  readTimestamp + shiftOffset,
 				  &local_underrun);
 	if ((size_t) num != resamp_outchunk) {
 		LOG(ALERT) << "Receive error " << num;

Transceiver52M/radioInterfaceResamp.cpp

@@ -188,7 +188,7 @@ void RadioInterfaceResamp::pullBuffer()
 	num_recv = mRadio->readSamples(convertRecvBuffer,
 				       resamp_outchunk,
 				       &overrun,
-				       readTimestamp,
+				       readTimestamp + shiftOffset,
 				       &local_underrun);
 	if (num_recv != (int) resamp_outchunk) {
 		LOG(ALERT) << "Receive error " << num_recv;

Transceiver52M/radioVector.cpp

@@ -74,25 +74,31 @@ bool radioVector::setVector(signalVector *vector, size_t chan)
 	return true;
 }
 
-noiseVector::noiseVector(size_t size)
+avgVector::avgVector(size_t max)
-	: std::vector<float>(size), itr(0)
+	: std::vector<float>(0), itr(0)
 {
+	this->max = max;
 }
 
-float noiseVector::avg() const
+float avgVector::avg() const
 {
 	float val = 0.0;
 
+	if (!size())
+		return 0.0f;
+
 	for (size_t i = 0; i < size(); i++)
 		val += (*this)[i];
 
 	return val / (float) size();
 }
 
-bool noiseVector::insert(float val)
+bool avgVector::insert(float val)
 {
-	if (!size())
+	if (size() < max) {
-		return false;
+		push_back(val);
+		return true;
+	}
 
 	if (itr >= this->size())
 		itr = 0;
@@ -102,6 +108,16 @@ bool noiseVector::insert(float val)
 	return true;
 }
 
+bool avgVector::full() const
+{
+	return size() >= max;
+}
+
+void avgVector::reset()
+{
+	resize(0);
+}
+
 GSM::Time VectorQueue::nextTime() const
 {
 	GSM::Time retVal;

Transceiver52M/radioVector.h

@@ -46,14 +46,17 @@ private:
 	GSM::Time mTime;
 };
 
-class noiseVector : std::vector<float> {
+class avgVector : std::vector<float> {
 public:
-	noiseVector(size_t size = 0);
+	avgVector(size_t size = 0);
 	bool insert(float val);
+	bool full() const;
 	float avg() const;
+	void reset();
 
 private:
 	size_t itr;
+	size_t max;
 };
 
 class VectorFIFO : public InterthreadQueue<radioVector> { };

Transceiver52M/sch.c

@@ -0,0 +1,219 @@
+#include <complex.h>
+#include <stdio.h>
+#include <math.h>
+#include <string.h>
+
+#include <osmocom/core/bits.h>
+#include <osmocom/core/conv.h>
+#include <osmocom/core/utils.h>
+#include <osmocom/core/crcgen.h>
+
+#include "sch.h"
+
+/* GSM 04.08, 9.1.30 Synchronization channel information */
+struct sch_packed_info {
+	ubit_t t1_hi[2];
+	ubit_t bsic[6];
+	ubit_t t1_md[8];
+	ubit_t t3p_hi[2];
+	ubit_t t2[5];
+	ubit_t t1_lo[1];
+	ubit_t t3p_lo[1];
+} __attribute__((packed));
+
+struct sch_burst {
+	sbit_t tail0[3];
+	sbit_t data0[39];
+	sbit_t etsc[64];
+	sbit_t data1[39];
+	sbit_t tail1[3];
+	sbit_t guard[8];
+} __attribute__((packed));
+
+static const uint8_t sch_next_output[][2] = {
+	{ 0, 3 }, { 1, 2 }, { 0, 3 }, { 1, 2 },
+	{ 3, 0 }, { 2, 1 }, { 3, 0 }, { 2, 1 },
+	{ 3, 0 }, { 2, 1 }, { 3, 0 }, { 2, 1 },
+	{ 0, 3 }, { 1, 2 }, { 0, 3 }, { 1, 2 },
+};
+
+static const uint8_t sch_next_state[][2] = {
+	{  0,  1 }, {  2,  3 }, {  4,  5 }, {  6,  7 },
+	{  8,  9 }, { 10, 11 }, { 12, 13 }, { 14, 15 },
+	{  0,  1 }, {  2,  3 }, {  4,  5 }, {  6,  7 },
+	{  8,  9 }, { 10, 11 }, { 12, 13 }, { 14, 15 },
+};
+
+static const struct osmo_conv_code gsm_conv_sch = {
+	.N = 2,
+	.K = 5,
+	.len = GSM_SCH_UNCODED_LEN,
+	.next_output = sch_next_output,
+	.next_state  = sch_next_state,
+};
+
+const struct osmo_crc16gen_code gsm0503_sch_crc10 = {
+	.bits = 10,
+	.poly = 0x175,
+	.init = 0x000,
+	.remainder = 0x3ff,
+};
+
+#define GSM_MAX_BURST_LEN	157
+#define GSM_SYM_RATE		(1625e3 / 6)
+
+/* Pre-generated FCCH measurement tone */
+static complex float fcch_ref[GSM_MAX_BURST_LEN];
+
+int float_to_sbit(const float *in, sbit_t *out, float scale, int len)
+{
+	int i;
+
+	for (i = 0; i < len; i++) {
+		out[i] = (in[i] - 0.5f) * scale;
+	}
+
+	return 0;
+}
+
+/* Check if FN contains a SCH burst */
+int gsm_sch_check_fn(int fn)
+{
+	int fn51 = fn % 51;
+
+	switch (fn51) {
+	case 1:
+	case 11:
+	case 21:
+	case 31:
+	case 41:
+		return 1;
+	}
+
+	return 0;
+}
+
+/* SCH (T1, T2, T3p) to full FN value */
+int gsm_sch_to_fn(struct sch_info *sch)
+{
+	int t1 = sch->t1;
+	int t2 = sch->t2;
+	int t3p = sch->t3p;
+
+	if ((t1 < 0) || (t2 < 0) || (t3p < 0))
+		return -1;
+	int tt;
+	int t3 = t3p * 10 + 1;
+
+	if (t3 < t2)
+		tt = (t3 + 26) - t2;
+	else
+		tt = (t3 - t2) % 26;
+
+	return t1 * 51 * 26 + tt * 51 + t3;
+}
+
+/* Parse encoded SCH message */
+int gsm_sch_parse(const uint8_t *info, struct sch_info *desc)
+{
+	struct sch_packed_info *p = (struct sch_packed_info *) info;
+
+	desc->bsic = (p->bsic[0] << 0) | (p->bsic[1] << 1) |
+		     (p->bsic[2] << 2) | (p->bsic[3] << 3) |
+		     (p->bsic[4] << 4);
+
+	desc->t1 = (p->t1_lo[0] << 0) | (p->t1_md[0] << 1) |
+		   (p->t1_md[1] << 2) | (p->t1_md[2] << 3) |
+		   (p->t1_md[3] << 4) | (p->t1_md[4] << 5) |
+		   (p->t1_md[5] << 6) | (p->t1_md[6] << 7) |
+		   (p->t1_md[7] << 8) | (p->t1_hi[0] << 9) |
+		   (p->t1_hi[1] << 10);
+
+	desc->t2 = (p->t2[0] << 0) | (p->t2[1] << 1) |
+		   (p->t2[2] << 2) | (p->t2[3] << 3) |
+		   (p->t2[4] << 4);
+
+	desc->t3p = (p->t3p_lo[0] << 0) | (p->t3p_hi[0] << 1) |
+		    (p->t3p_hi[1] << 2);
+
+	return 0;
+}
+
+/* From osmo-bts */
+int gsm_sch_decode(uint8_t *info, sbit_t *data)
+{
+	int rc;
+	ubit_t uncoded[GSM_SCH_UNCODED_LEN];
+
+	osmo_conv_decode(&gsm_conv_sch, data, uncoded);
+
+	rc = osmo_crc16gen_check_bits(&gsm0503_sch_crc10,
+				      uncoded, GSM_SCH_INFO_LEN,
+				      uncoded + GSM_SCH_INFO_LEN);
+	if (rc)
+		return -1;
+
+	memcpy(info, uncoded, GSM_SCH_INFO_LEN * sizeof(ubit_t));
+
+	return 0;
+}
+
+#define FCCH_TAIL_BITS_LEN	3
+#define FCCH_DATA_LEN		142
+
+/* Compute FCCH frequency offset */
+double gsm_fcch_offset(float *burst, int len)
+{
+	int i, start, end;
+	float a, b, c, d, ang, avg = 0.0f;
+	double freq;
+
+	if (len > GSM_MAX_BURST_LEN)
+		len = GSM_MAX_BURST_LEN;
+
+	for (i = 0; i < len; i++) {
+		a = burst[2 * i + 0];
+		b = burst[2 * i + 1];
+		c = crealf(fcch_ref[i]);
+		d = cimagf(fcch_ref[i]);
+
+		burst[2 * i + 0] = a * c - b * d;
+		burst[2 * i + 1] = a * d + b * c;
+	}
+
+	start = FCCH_TAIL_BITS_LEN;
+	end = start + FCCH_DATA_LEN;
+
+	for (i = start; i < end; i++) {
+		a = cargf(burst[2 * (i - 1) + 0] +
+			  burst[2 * (i - 1) + 1] * I);
+		b = cargf(burst[2 * i + 0] +
+			  burst[2 * i + 1] * I);
+
+		ang = b - a;
+
+		if (ang > M_PI)
+			ang -= 2 * M_PI;
+		else if (ang < -M_PI)
+			ang += 2 * M_PI;
+
+		avg += ang;
+	}
+
+	avg /= (float) (end - start);
+	freq = avg / (2 * M_PI) * GSM_SYM_RATE;
+
+	return freq;
+}
+
+/* Generate FCCH measurement tone */
+static __attribute__((constructor)) void init()
+{
+	int i;
+	double freq = 0.25;
+
+	for (i = 0; i < GSM_MAX_BURST_LEN; i++) {
+		fcch_ref[i] = sin(2 * M_PI * freq * (double) i) +
+			      cos(2 * M_PI * freq * (double) i) * I;
+	}
+}

Transceiver52M/sch.h

@@ -0,0 +1,26 @@
+#ifndef _SCH_H_
+#define _SCH_H_
+
+#include <osmocom/core/bits.h>
+
+struct sch_info  {
+	int bsic;
+	int t1;
+	int t2;
+	int t3p;
+};
+
+#define GSM_SCH_INFO_LEN		25
+#define GSM_SCH_UNCODED_LEN		35
+#define GSM_SCH_CODED_LEN		78
+
+int gsm_sch_decode(uint8_t *sb_info, sbit_t *burst);
+int gsm_sch_parse(const uint8_t *sb_info, struct sch_info *desc);
+int gsm_sch_to_fn(struct sch_info *sch);
+int gsm_sch_check_fn(int fn);
+
+double gsm_fcch_offset(float *burst, int len);
+
+int float_to_sbit(const float *in, sbit_t *out, float scale, int len);
+
+#endif /* _SCH_H_ */

Transceiver52M/sigProcLib.cpp

@@ -78,6 +78,7 @@ struct CorrelationSequence {
 
   signalVector *sequence;
   void         *buffer;
+  void         *history;
   float        toa;
   complex      gain;
 };
@@ -111,6 +112,7 @@ struct PulseSequence {
 
 CorrelationSequence *gMidambles[] = {NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL};
 CorrelationSequence *gRACHSequence = NULL;
+CorrelationSequence *gSCHSequence = NULL;
 PulseSequence *GSMPulse = NULL;
 PulseSequence *GSMPulse1 = NULL;
 
@@ -131,6 +133,7 @@ void sigProcLibDestroy()
   delete GMSKRotation1;
   delete GMSKReverseRotation1;
   delete gRACHSequence;
+  delete gSCHSequence;
   delete GSMPulse;
   delete GSMPulse1;
 
@@ -139,6 +142,7 @@ void sigProcLibDestroy()
   GMSKReverseRotationN = NULL;
   GMSKReverseRotation1 = NULL;
   gRACHSequence = NULL;
+  gSCHSequence = NULL;
   GSMPulse = NULL;
   GSMPulse1 = NULL;
 }
@@ -395,8 +399,10 @@ signalVector *convolve(const signalVector *x,
     break;
   case CUSTOM:
     if (start < h->size() - 1) {
-      head = h->size() - start;
+      if (x->getStart() < h->size() - 1) {
-      append = true;
+        head = h->size() - start;
+        append = true;
+      }
     }
     if (start + len > x->size()) {
       tail = start + len - x->size();
@@ -1274,6 +1280,69 @@ release:
   return status;
 }
 
+bool generateSCHSequence(int sps)
+{
+  bool status = true;
+  float toa;
+  complex *data = NULL;
+  signalVector *autocorr = NULL;
+  signalVector *seq0 = NULL, *seq1 = NULL, *_seq1 = NULL;
+
+  delete gSCHSequence;
+
+  seq0 = modulateBurst(gSCHSynchSequence, 0, sps, false);
+  if (!seq0)
+    return false;
+
+  seq1 = modulateBurst(gSCHSynchSequence, 0, sps, true);
+  if (!seq1) {
+    status = false;
+    goto release;
+  }
+
+  conjugateVector(*seq1);
+
+  /* For SSE alignment, reallocate the midamble sequence on 16-byte boundary */
+  data = (complex *) convolve_h_alloc(seq1->size());
+  _seq1 = new signalVector(data, 0, seq1->size());
+  _seq1->setAligned(true);
+  memcpy(_seq1->begin(), seq1->begin(), seq1->size() * sizeof(complex));
+
+  autocorr = convolve(seq0, _seq1, autocorr, NO_DELAY);
+  if (!autocorr) {
+    status = false;
+    goto release;
+  }
+
+  gSCHSequence = new CorrelationSequence;
+  gSCHSequence->sequence = _seq1;
+  gSCHSequence->buffer = data;
+  gSCHSequence->gain = peakDetect(*autocorr, &toa, NULL);
+  gSCHSequence->history = new complex[_seq1->size()];
+
+  /* For 1 sps only
+   *     (Half of correlation length - 1) + midpoint of pulse shaping filer
+   *     20.5 = (64 / 2 - 1) + 1.5
+   */
+  if (sps == 1)
+    gSCHSequence->toa = toa - 32.5;
+  else
+    gSCHSequence->toa = 0.0;
+
+release:
+  delete autocorr;
+  delete seq0;
+  delete seq1;
+
+  if (!status) {
+    delete _seq1;
+    free(data);
+    gSCHSequence = NULL;
+  }
+
+  return status;
+}
+
 static float computePeakRatio(signalVector *corr,
                               int sps, float toa, complex amp)
 {
@@ -1424,6 +1493,71 @@ int detectRACHBurst(signalVector &rxBurst,
   return 1;
 }
 
+int detectSCHBurst(signalVector &burst,
+		    float thresh,
+		    int sps,
+		    complex *amp,
+		    float *toa, int state)
+{
+  int rc, start, target, head, tail, len;
+  float _toa;
+  complex _amp;
+  signalVector *corr, *_burst;
+  CorrelationSequence *sync;
+
+  if ((sps != 1) && (sps != 4))
+    return -1;
+
+  target = 3 + 39 + 64;
+
+  switch (state) {
+  case SCH_DETECT_NARROW:
+    head = 4;
+    tail = 4;
+    break;
+  case SCH_DETECT_FULL:
+  default:
+    head = target - 1;
+    tail = 39 + 3 + 9;
+    break;
+  }
+
+  start = (target - head) * sps - 1;
+  len = (head + tail) * sps;
+  sync = gSCHSequence;
+  corr = new signalVector(len);
+
+  _burst = new signalVector(burst, sync->sequence->size(), 5);
+
+  memcpy(_burst->begin() - sync->sequence->size(), sync->history,
+         sync->sequence->size() * sizeof(complex));
+
+  memcpy(sync->history, &burst.begin()[burst.size() - sync->sequence->size()],
+         sync->sequence->size() * sizeof(complex));
+
+  rc = detectBurst(*_burst, *corr, sync,
+                   thresh, sps, &_amp, &_toa, start, len);
+  delete corr;
+
+  if (rc < 0) {
+    return -1;
+  } else if (!rc) {
+    if (amp)
+      *amp = 0.0f;
+    if (toa)
+      *toa = 0.0f;
+    return 0;
+  }
+
+  /* Subtract forward search bits from delay */
+  if (toa)
+    *toa = _toa - head * sps;
+  if (amp)
+    *amp = _amp;
+
+  return 1;
+}
+
 /* 
  * Normal burst detection
  *
@@ -1717,6 +1851,11 @@ bool sigProcLibSetup(int sps)
     return false;
   }
 
+  if (!generateSCHSequence(1)) {
+    sigProcLibDestroy();
+    return false;
+  }
+
   generateDelayFilters();
 
   return true;

Transceiver52M/sigProcLib.h

@@ -158,6 +158,7 @@ bool generateMidamble(int sps, int tsc);
         @return Success.
 */
 bool generateRACHSequence(int sps);
+bool generateSCHSequence(int sps);
 
 /**
         Energy detector, checks to see if received burst energy is above a threshold.
@@ -187,6 +188,17 @@ int detectRACHBurst(signalVector &rxBurst,
                     complex *amplitude,
                     float* TOA);
 
+enum {
+	SCH_DETECT_FULL,
+	SCH_DETECT_NARROW,
+};
+
+int detectSCHBurst(signalVector &rxBurst,
+                    float detectThreshold,
+                    int sps,
+                    complex *amplitude,
+                    float* TOA, int state);
+
 /**
         Normal burst correlator, detector, channel estimator.
         @param rxBurst The received GSM burst of interest.

configure.ac

@@ -58,6 +58,9 @@ AC_TYPE_SIZE_T
 AC_HEADER_TIME
 AC_C_BIGENDIAN
 
+dnl checks for libraries
+PKG_CHECK_MODULES(LIBOSMOCORE, libosmocore  >= 0.3.9)
+
 AC_ARG_WITH(usrp1, [
     AS_HELP_STRING([--with-usrp1],
         [enable USRP1 gnuradio based transceiver])