mirror of https://github.com/g4klx/MMDVM.git
95 lines
2.8 KiB
C++
95 lines
2.8 KiB
C++
/*
|
|
* Copyright (C) 2025 by Rob Williams M1BGT
|
|
*
|
|
* 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 2 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, write to the Free Software
|
|
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
|
|
*/
|
|
|
|
#include <stdint.h>
|
|
//#include <cstdio> // Only required for additional debug
|
|
#include "Globals.h"
|
|
|
|
// Map from syndrome value to error bit index in DMR order
|
|
const int syndromeMap[8] = {
|
|
-1, // 0: no error
|
|
4, // syndrome 1 → P1 (bit 4)
|
|
5, // syndrome 2 → P2 (bit 5)
|
|
2, // syndrome 3 → D3 (bit 2)
|
|
6, // syndrome 4 → P3 (bit 6)
|
|
0, // syndrome 5 → D2 (bit 1)
|
|
3, // syndrome 6 → D4 (bit 3)
|
|
1, // syndrome 7 → D2 (bit 1)
|
|
};
|
|
|
|
// Decode DMR CACH Hamming(7,4)
|
|
bool decodeSingleDMRHamming74(uint8_t *received) {
|
|
/*
|
|
D1 2 3 4 P1 2 3
|
|
1 0 0 0 1 0 1. (5)
|
|
0 1 0 0 1 1 1. (7)
|
|
0 0 1 0 1 1 0. (3)
|
|
0 0 0 1 0 1 1 (6)
|
|
*/
|
|
|
|
uint8_t D1 = received[0];
|
|
uint8_t D2 = received[1];
|
|
uint8_t D3 = received[2];
|
|
uint8_t D4 = received[3];
|
|
|
|
uint8_t P1 = received[4];
|
|
uint8_t P2 = received[5];
|
|
uint8_t P3 = received[6];
|
|
|
|
// Calculate syndrome bits
|
|
uint8_t S1 = P1 ^ D1 ^ D2 ^ D3;
|
|
uint8_t S2 = P2 ^ D2 ^ D3 ^ D4;
|
|
uint8_t S3 = P3 ^ D1 ^ D2 ^ D4;
|
|
|
|
uint8_t syndrome = (S3 << 2) | (S2 << 1) | S1;
|
|
|
|
if (syndrome != 0) {
|
|
int errorBit = syndromeMap[syndrome];
|
|
if (errorBit != -1) {
|
|
DEBUG2("Error detected, flipping bit.", errorBit);
|
|
received[errorBit] ^= 1; // Flip bit
|
|
|
|
// Return false to indicate a change was made (it might be good now)
|
|
return false;
|
|
}
|
|
}
|
|
|
|
// No bits flipped - good
|
|
return true;
|
|
}
|
|
|
|
bool decodeDMRHamming74(uint8_t *received) {
|
|
// Check it multiple times to make sure we know all are valid
|
|
|
|
//char receivedLog[28];
|
|
//snprintf(receivedLog, 28, "Input Hamming 7,4: %d%d%d%d %d%d%d",
|
|
// received[0], received[1], received[2], received[3],
|
|
// received[4], received[5], received[6]);
|
|
//DEBUG1(receivedLog);
|
|
|
|
// The first pass may result in a bit flip, the second must not
|
|
for(uint8_t i=0;i<2;i++)
|
|
{
|
|
if(decodeSingleDMRHamming74(received)) {
|
|
return true;
|
|
}
|
|
}
|
|
|
|
return false;
|
|
}
|