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NXDN -- Implement Secondary 1/2 Decoder; Misc;

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lwvmobile
2023-11-15 16:21:25 -05:00
parent d6160f7b7a
commit e6da485117
3 changed files with 149 additions and 19 deletions
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82
src/3.c
View File

@@ -2,6 +2,86 @@
* 3.c
* Placeholder File 3 -- This file is for temporary code storage
*
* A 1/2 Rate Convolutional Decoder for NXDN/M17/YSF
* Used as a secondary decoder in case convolutional decoder fails (second opinion)
*-----------------------------------------------------------------------------*/
#include "dsd.h"
static const int PARITY[] = {0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1};
// trellis_1_2 encode: source is in bits, result in bits
void trellis_encode(uint8_t result[], const uint8_t source[], int result_len, int reg)
{
for (int i=0; i<result_len; i+=2) {
reg = (reg << 1) | source[i>>1];
result[i] = PARITY[reg & 0x19];
result[i+1] = PARITY[reg & 0x17];
}
}
// simplified trellis 2:1 decode; source and result in bits
// assumes that encoding was done with NTEST trailing zero bits
// result_len should be set to the actual number of data bits
// in the original unencoded message (excl. these trailing bits)
void trellis_decode(uint8_t result[], const uint8_t source[], int result_len)
{
int reg = 0;
int min_d;
int min_bt;
static const int NTEST = 4;
static const int NTESTC = 1 << NTEST;
uint8_t bt[NTEST];
uint8_t tt[NTEST*2];
int dstats[4];
int sum;
for (int p=0; p < 4; p++)
dstats[p] = 0;
for (int p=0; p < result_len; p++) {
for (int i=0; i<NTESTC; i++) {
bt[0] = (i&8)>>3;
bt[1] = (i&4)>>2;
bt[2] = (i&2)>>1;
bt[3] = (i&1);
trellis_encode(tt, bt, NTEST*2, reg);
sum=0;
for (int j=0; j<NTEST*2; j++) {
sum += tt[j] ^ source[p*2+j];
}
if (i == 0 || sum < min_d) {
min_d = sum;
min_bt = bt[0];
}
}
result[p] = min_bt;
reg = (reg << 1) | min_bt;
dstats[(min_d > 3) ? 3 : min_d] += 1;
}
//debug output
// fprintf (stderr, "\n stats\t%d %d %d %d\n", dstats[0], dstats[1], dstats[2], dstats[3]);
}
//Original Copyright/License
/* -*- c++ -*- */
/*
* NXDN Encoder/Decoder (C) Copyright 2019 Max H. Parke KA1RBI
*
* This file is part of OP25
*
*-----------------------------------------------------------------------------*/
* This 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, or (at your option)
* any later version.
*
* This software 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 software; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/

84
src/nxdn_deperm.c
View File

@@ -52,7 +52,7 @@ void nxdn_deperm_facch(dsd_opts * opts, dsd_state * state, uint8_t bits[144])
uint8_t deperm[144]; //144
uint8_t depunc[192]; //192
uint8_t trellis_buf[96]; //96
uint16_t crc = 0; //crc calculated by function
uint16_t crc = 1; //crc calculated by function
uint16_t check = 0; //crc from payload for comparison
int out;
@@ -111,6 +111,30 @@ void nxdn_deperm_facch(dsd_opts * opts, dsd_state * state, uint8_t bits[144])
check = check | trellis_buf[84+i]; //80
}
//debug
// if (crc == check)
// fprintf (stderr, " Pass 1 ");
//if the crc fails, attempt again with the other trellis decoder
if (crc != check)
{
//debug
// fprintf (stderr, " Pass 2 ");
crc = 1; check = 0;
memset (trellis_buf, 0, sizeof(trellis_buf));
memset (m_data, 0, sizeof(m_data));
trellis_decode(trellis_buf, depunc, 92);
//fill m_data bytes with trellis_buf
for(int i = 0; i < 12; i++)
m_data[i] = (uint8_t)ConvertBitIntoBytes(&trellis_buf[i*8], 8);
crc = crc12f (trellis_buf, 84);
for (int i = 0; i < 12; i++)
{
check = check << 1;
check = check | trellis_buf[i+84];
}
}
if (crc == check) NXDN_Elements_Content_decode(opts, state, 1, trellis_buf);
// else if (opts->aggressive_framesync == 0) NXDN_Elements_Content_decode(opts, state, 0, trellis_buf);
@@ -145,7 +169,7 @@ void nxdn_deperm_sacch(dsd_opts * opts, dsd_state * state, uint8_t bits[60])
memset (trellis_buf, 0, sizeof(trellis_buf));
int o = 0;
uint8_t crc = 0; //value computed by crc6 on payload
uint8_t crc = 1; //value computed by crc6 on payload
uint8_t check = 0; //value pulled from last 6 bits
int sf = 0;
int ran = 0;
@@ -212,6 +236,30 @@ void nxdn_deperm_sacch(dsd_opts * opts, dsd_state * state, uint8_t bits[60])
check = check | trellis_buf[i+26];
}
//debug
// if (crc == check)
// fprintf (stderr, " Pass 1 ");
//if the crc fails, attempt again with the other trellis decoder
if (crc != check)
{
//debug
// fprintf (stderr, " Pass 2 ");
crc = 1; check = 0;
memset (trellis_buf, 0, sizeof(trellis_buf));
memset (m_data, 0, sizeof(m_data));
trellis_decode(trellis_buf, depunc, 32);
//fill m_data bytes with trellis_buf
for(int i = 0; i < 4; i++)
m_data[i] = (uint8_t)ConvertBitIntoBytes(&trellis_buf[i*8], 8);
crc = crc6(trellis_buf, 26); //32
for (int i = 0; i < 6; i++)
{
check = check << 1;
check = check | trellis_buf[i+26];
}
}
//FIRST! If part of a non_superframe, and CRC is good, send directly to NXDN_Elements_Content_decode
if (state->nxdn_sacch_non_superframe == TRUE)
{
@@ -284,12 +332,12 @@ void nxdn_deperm_sacch(dsd_opts * opts, dsd_state * state, uint8_t bits[60])
fprintf (stderr, "PF %d/4", part_of_frame+1);
if (crc != check)
{
fprintf (stderr, "%s", KRED);
fprintf (stderr, " (CRC ERR)");
fprintf (stderr, "%s", KNRM);
}
// if (crc != check)
// {
// fprintf (stderr, "%s", KRED);
// fprintf (stderr, " (CRC ERR)");
// fprintf (stderr, "%s", KNRM);
// }
//reset scrambler seed to key value on new superframe
if (part_of_frame == 0 && state->nxdn_cipher_type == 0x1) state->payload_miN = 0;
@@ -319,16 +367,16 @@ void nxdn_deperm_sacch(dsd_opts * opts, dsd_state * state, uint8_t bits[60])
NXDN_SACCH_Full_decode (opts, state);
}
// if (opts->payload == 1)
// {
// fprintf (stderr, "\n");
// fprintf (stderr, " SACCH SF Segment #%d ", part_of_frame+1);
// for (int i = 0; i < 4; i++)
// {
// fprintf (stderr, "[%02X]", m_data[i]);
// }
// // if (crc != check) fprintf (stderr, " CRC ERR - %02X %02X", crc, check);
// }
if (opts->payload == 1)
{
fprintf (stderr, "\n");
fprintf (stderr, " SACCH SF Segment #%d ", part_of_frame+1);
for (int i = 0; i < 4; i++)
{
fprintf (stderr, "[%02X]", m_data[i]);
}
if (crc != check) fprintf (stderr, " CRC ERR - %02X %02X", crc, check);
}
}