Transceiver52M: Preallocate head room for burst correlation

Set a transceiver high level length value that specifies the largest
number of complex or real filter taps that we will encounter. This
allows preallocation of head room and prevents an extra allocation and
copy on every incoming receive burst.

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

1 files changed, 11 insertions, 4 deletions

diff --git a/Transceiver52M/radioInterface.cpp b/Transceiver52M/radioInterface.cpp
index d05dcf2..5cf34de 100644
--- a/Transceiver52M/radioInterface.cpp
+++ b/Transceiver52M/radioInterface.cpp
@@ -239,12 +239,19 @@ bool RadioInterface::driveReceiveRadio()
   const int symbolsPerSlot = gSlotLen + 8;
   int burstSize = (symbolsPerSlot + (tN % 4 == 0)) * mSPSRx;
 
-  // while there's enough data in receive buffer, form received 
-  //    GSM bursts and pass up to Transceiver
-  // Using the 157-156-156-156 symbols per timeslot format.
+  /* 
+   * Pre-allocate head room for the largest correlation size
+   * so we can later avoid a re-allocation and copy
+   * */
+  size_t head = GSM::gRACHSynchSequence.size();
+
+  /*
+   * Form receive bursts and pass up to transceiver. Use repeating
+   * pattern of 157-156-156-156 symbols per timeslot
+   */
   while (recvSz > burstSize) {
     for (size_t i = 0; i < mChans; i++) {
-      burst = new radioVector(burstSize, rcvClock);
+      burst = new radioVector(burstSize, head, rcvClock);
 
       unRadioifyVector((float *) (recvBuffer[i]->begin() + readSz), *burst);
       if (mReceiveFIFO[i].size() < 32)