summaryrefslogtreecommitdiff
path: root/gsm-receiver/src/lib/decoder/openbtsstuff/GSML1FEC.cpp
blob: 1c99a0f51f4a76c9662230bda875dac5fc15c869 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
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
personal git repositories of Harald Welte. Your mileage may vary