From 8d2bc49fb9e0c9a5fbd75aa3cad207608e72bf99 Mon Sep 17 00:00:00 2001
From: Piotr Krysik <perper@o2.pl>
Date: Tue, 30 Jun 2009 23:03:33 +0200
Subject: moved gsm-receiver into directory - preparation to move to airprobe

---
 .../src/lib/decoder/openbtsstuff/GSML1FEC.cpp      | 256 +++++++++++++++++++++
 1 file changed, 256 insertions(+)
 create mode 100644 gsm-receiver/src/lib/decoder/openbtsstuff/GSML1FEC.cpp

(limited to 'gsm-receiver/src/lib/decoder/openbtsstuff/GSML1FEC.cpp')

diff --git a/gsm-receiver/src/lib/decoder/openbtsstuff/GSML1FEC.cpp b/gsm-receiver/src/lib/decoder/openbtsstuff/GSML1FEC.cpp
new file mode 100644
index 0000000..1c99a0f
--- /dev/null
+++ b/gsm-receiver/src/lib/decoder/openbtsstuff/GSML1FEC.cpp
@@ -0,0 +1,256 @@
+/*
+* Copyright 2008 Free Software Foundation, Inc.
+*
+* This software is distributed under the terms of the GNU Public License.
+* See the COPYING file in the main directory for details.
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+*/
+
+
+#define NDEBUG
+
+
+#include "GSML1FEC.h"
+#include "GSMCommon.h"
+#include "RxBurst.h"
+//#include "GSMSAPMux.h"
+//#include "GSMConfig.h"
+#include "GSMTDMA.h"
+#include "GSM610Tables.h"
+#include "Assert.h"
+
+
+using namespace std;
+using namespace GSM;
+
+/*
+ Compilation flags:
+ NOCONTROL Compile without referencing control layer functions.
+*/
+
+
+/*
+
+ Notes on reading the GSM specifications.
+
+ Every FEC section in GSM 05.03 uses standard names for the bits at
+ different stages of the encoding/decoding process.
+
+ This is all described formally in GSM 05.03 2.2.
+
+ "d" -- data bits.  The actual payloads from L2 and the vocoders.
+ "p" -- parity bits.  These are calculated from d.
+ "u" -- uncoded bits.  A concatenation of d, p and inner tail bits.
+ "c" -- coded bits.  These are the convolutionally encoded from u.
+ "i" -- interleaved bits.  These are the output of the interleaver.
+ "e" -- "encrypted" bits.  These are the channel bits in the radio bursts.
+
+ The "e" bits are call "encrypted" even when encryption is not used.
+
+ The encoding process is:
+
+ L2 -> d -> -> calc p -> u -> c -> i -> e -> radio bursts
+
+ The decoding process is:
+
+ radio bursts -> e -> i -> c -> u -> check p -> d -> L2
+
+ Bit ordering in d is LSB-first in each octet.
+ Bit ordering everywhere else in the OpenBTS code is MSB-first
+ in every field to give contiguous fields across byte boundaries.
+ We use the BitVector::LSB8MSB() method to translate.
+
+*/
+
+TCHFACCHL1Decoder::TCHFACCHL1Decoder(const TDMAMapping& wMapping)
+    : mTCHU(189), mTCHD(260), mC(456),
+    mClass1_c(mC.head(378)), mClass1A_d(mTCHD.head(50)), mClass2_c(mC.segment(378, 78)),
+    mTCHParity(0x0b, 3, 50), mMapping(wMapping)
+{
+  for (int i = 0; i < 8; i++) {
+    mI[i] = SoftVector(114);
+  }
+}
+
+
+void TCHFACCHL1Decoder::writeLowSide(const RxBurst& inBurst)
+{
+  OBJDCOUT("TCHFACCHL1Decoder::writeLowSide " << inBurst);
+  // If the channel is closed, ignore the burst.
+// if (!active()) {
+//  OBJDCOUT("TCHFACCHL1Decoder::writeLowSide not active, ignoring input");
+//  return;
+// }
+  processBurst(inBurst);
+}
+
+bool TCHFACCHL1Decoder::processBurst( const RxBurst& inBurst)
+{
+  // Accept the burst into the deinterleaving buffer.
+  // Return true if we are ready to interleave.
+
+  // TODO -- One quick test of burst validity is to look at the tail bits.
+  // We could do that as a double-check against putting garbage into
+  // the interleaver or accepting bad parameters.
+
+  // Get the physical parameters of the burst.
+  // RSSI is dB wrt full scale.
+// mRSSI = inBurst.RSSI();
+  // Timing error is a float in symbol intervals.
+// mTimingError = inBurst.timingError();
+  // This flag is used as a half-ass semaphore.
+  // It is cleared when the new value is read.
+// mPhyNew = true;
+
+  // The reverse index runs 0..3 as the bursts arrive.
+  // It is the "B" index of GSM 05.03 3.1.3 and 3.1.4.
+  int B = mMapping.reverseMapping(inBurst.time().FN()) % 8;
+  // A negative value means that the demux is misconfigured.
+  assert(B >= 0);
+  OBJDCOUT("TCHFACCHL1Decoder::processBurst B=" << B << " " << inBurst);
+
+  // Pull the data fields (e-bits) out of the burst and put them into i[B][].
+  // GSM 05.03 3.1.4
+  inBurst.data1().copyToSegment(mI[B], 0);
+  inBurst.data2().copyToSegment(mI[B], 57);
+
+  // Every 4th frame is the start of a new block.
+  // So if this isn't a "4th" frame, return now.
+  if (B % 4 != 3) return false;
+
+  // Deinterleave according to the diagonal "phase" of B.
+  // See GSM 05.03 3.1.3.
+  // Deinterleaves i[] to c[]
+  if (B == 3) deinterleave(4);
+  else deinterleave(0);
+
+  // See if this was the end of a stolen frame, GSM 05.03 4.2.5.
+  bool stolen = inBurst.Hl();
+  OBJDCOUT("TCHFACCHL!Decoder::processBurst Hl=" << inBurst.Hl() << " Hu=" << inBurst.Hu());
+  /* if (stolen) {
+    if (decode()) {
+     OBJDCOUT("TCHFACCHL1Decoder::processBurst good FACCH frame");
+     countGoodFrame();
+     handleGoodFrame();
+    } else {
+     OBJDCOUT("TCHFACCHL1Decoder::processBurst bad FACCH frame");
+     countBadFrame();
+    }
+   }*/
+
+  // Always feed the traffic channel, even on a stolen frame.
+  // decodeTCH will handle the GSM 06.11 bad frmae processing.
+  bool traffic = decodeTCH(stolen);
+//  if (traffic) {
+  OBJDCOUT("TCHFACCHL1Decoder::processBurst good TCH frame");
+//  countGoodFrame();
+  // Don't let the channel timeout.
+  // mLock.lock();
+  // mT3109.set();
+  // mLock.unlock();
+//  }
+// else countBadFrame();
+
+  return traffic;
+}
+
+void TCHFACCHL1Decoder::deinterleave(int blockOffset )
+{
+  OBJDCOUT("TCHFACCHL1Decoder::deinterleave blockOffset=" << blockOffset);
+  for (int k = 0; k < 456; k++) {
+    int B = ( k + blockOffset ) % 8;
+    int j = 2 * ((49 * k) % 57) + ((k % 8) / 4);
+    mC[k] = mI[B][j];
+    mI[B][j] = 0.5F;
+    //OBJDCOUT("deinterleave k="<<k<<" B="<<B<<" j="<<j);
+  }
+}
+
+bool TCHFACCHL1Decoder::decodeTCH(bool stolen)
+{
+  // GSM 05.02 3.1.2, but backwards
+
+  // If the frame wasn't stolen, we'll update this with parity later.
+  bool good = !stolen;
+
+  // Good or bad, we will be sending *something* to the speech channel.
+  // Allocate it in this scope.
+  unsigned char * newFrame = new unsigned char[33];
+
+  if (!stolen) {
+
+    // 3.1.2.2
+    // decode from c[] to u[]
+    mClass1_c.decode(mVCoder, mTCHU);
+    //mC.head(378).decode(mVCoder,mTCHU);
+
+    // 3.1.2.2
+    // copy class 2 bits c[] to d[]
+    mClass2_c.sliced().copyToSegment(mTCHD, 182);
+    //mC.segment(378,78).sliced().copyToSegment(mTCHD,182);
+
+    // 3.1.2.1
+    // copy class 1 bits u[] to d[]
+    for (unsigned k = 0; k <= 90; k++) {
+      mTCHD[2*k] = mTCHU[k];
+      mTCHD[2*k+1] = mTCHU[184-k];
+    }
+
+    // 3.1.2.1
+    // check parity of class 1A
+    unsigned sentParity = (~mTCHU.peekField(91, 3)) & 0x07;
+    //unsigned calcParity = mTCHD.head(50).parity(mTCHParity) & 0x07;
+    unsigned calcParity = mClass1A_d.parity(mTCHParity) & 0x07;
+
+    // 3.1.2.2
+    // Check the tail bits, too.
+    unsigned tail = mTCHU.peekField(185, 4);
+
+    OBJDCOUT("TCHFACCHL1Decoder::decodeTCH c[]=" << mC);
+    //OBJDCOUT("TCHFACCHL1Decoder::decodeTCH u[]=" << mTCHU);
+    OBJDCOUT("TCHFACCHL1Decoder::decodeTCH d[]=" << mTCHD);
+    OBJDCOUT("TCHFACCHL1Decoder::decodeTCH sentParity=" << sentParity
+             << " calcParity=" << calcParity << " tail=" << tail);
+    good = (sentParity == calcParity) && (tail == 0);
+    if (good) {
+      // Undo Um's importance-sorted bit ordering.
+      // See GSM 05.03 3.1 and Tablee 2.
+      BitVector payload = mVFrame.payload();
+      mTCHD.unmap(g610BitOrder, 260, payload);
+      mVFrame.pack(newFrame);
+      // Save a copy for bad frame processing.
+      memcpy(mPrevGoodFrame, newFrame, 33);
+      return true;
+    }
+  }
+
+  if (!good) {
+    // TODO -- Bad frame processing, GSM 06.11.
+    // For now, just repeat the last good frame.
+    // TODO -- Need to apply attenuation and randomization of grid positions.
+    memcpy(newFrame, mPrevGoodFrame, 33);
+    //d_gsm_file.write((char *)newFrame, 33);
+  }
+
+  
+  // Good or bad, we must feed the speech channel.
+// mSpeechQ.write(newFrame);
+
+
+  return false;
+}
+
+// vim: ts=4 sw=4
-- 
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