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358 lines
12 KiB
C++
358 lines
12 KiB
C++
///////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2020 Edouard Griffiths, F4EXB <f4exb06@gmail.com> //
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// //
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// Inspired by: https://github.com/myriadrf/LoRa-SDR //
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// //
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// This program is free software; you can redistribute it and/or modify //
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// it under the terms of the GNU General Public License as published by //
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// the Free Software Foundation as version 3 of the License, or //
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// (at your option) any later version. //
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// //
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// This program is distributed in the hope that it will be useful, //
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// but WITHOUT ANY WARRANTY; without even the implied warranty of //
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the //
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// GNU General Public License V3 for more details. //
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// //
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// You should have received a copy of the GNU General Public License //
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// along with this program. If not, see <http://www.gnu.org/licenses/>. //
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///////////////////////////////////////////////////////////////////////////////////
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#ifndef INCLUDE_CHIRPCHATDEMODDECODERLORA_H
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#define INCLUDE_CHIRPCHATDEMODDECODERLORA_H
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#include <vector>
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#include <QByteArray>
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class ChirpChatDemodDecoderLoRa
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{
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public:
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enum ParityStatus
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{
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ParityUndefined,
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ParityError,
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ParityCorrected,
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ParityOK
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};
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static void decodeBytes(
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QByteArray& bytes,
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const std::vector<unsigned short>& inSymbols,
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unsigned int nbSymbolBits,
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bool hasHeader,
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bool& hasCRC,
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unsigned int& nbParityBits,
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unsigned int& packetLength,
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bool& earlyEOM,
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int& headerParityStatus,
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bool& headerCRCStatus,
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int& payloadParityStatus,
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bool& payloadCRCStatus
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);
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static void getCodingMetrics(
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unsigned int nbSymbolBits,
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unsigned int nbParityBits,
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unsigned int packetLength,
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bool hasHeader,
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bool hasCRC,
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unsigned int& numSymbols,
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unsigned int& numCodewords
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);
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private:
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static void decodeHeader(
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const std::vector<unsigned short>& inSymbols,
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unsigned int nbSymbolBits,
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bool& hasCRC,
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unsigned int& nbParityBits,
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unsigned int& packetLength,
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int& headerParityStatus,
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bool& headerCRCStatus
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);
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static const unsigned int headerParityBits = 4;
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static const unsigned int headerSymbols = 8;
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static const unsigned int headerCodewords = 5;
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/***********************************************************************
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* Round functions
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**********************************************************************/
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static inline unsigned roundUp(unsigned num, unsigned factor)
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{
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return ((num + factor - 1) / factor) * factor;
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}
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/***********************************************************************
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* https://en.wikipedia.org/wiki/Gray_code
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**********************************************************************/
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/*
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* This function converts an unsigned binary
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* number to reflected binary Gray code.
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*
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* The operator >> is shift right. The operator ^ is exclusive or.
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*/
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static inline unsigned short binaryToGray16(unsigned short num)
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{
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return num ^ (num >> 1);
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}
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/***********************************************************************
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* Diagonal deinterleaver
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**********************************************************************/
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static inline void diagonalDeinterleaveSx(
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const uint16_t *symbols,
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const unsigned int numSymbols,
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uint8_t *codewords,
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const unsigned int nbSymbolBits,
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const unsigned int nbParityBits)
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{
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for (unsigned int x = 0; x < numSymbols / (4 + nbParityBits); x++)
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{
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const unsigned int cwOff = x*nbSymbolBits;
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const unsigned int symOff = x*(4 + nbParityBits);
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for (unsigned int k = 0; k < 4 + nbParityBits; k++)
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{
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for (unsigned int m = 0; m < nbSymbolBits; m++)
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{
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const unsigned int i = (m + k) % nbSymbolBits;
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const auto bit = (symbols[symOff + k] >> m) & 0x1;
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codewords[cwOff + i] |= (bit << k);
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}
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}
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}
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}
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/***********************************************************************
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* Whitening generator reverse engineered from Sx1272 data stream.
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* Same as above but using the actual interleaved LFSRs.
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**********************************************************************/
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static inline void Sx1272ComputeWhiteningLfsr(uint8_t *buffer, uint16_t bufferSize, const int bitOfs, const unsigned int nbParityBits)
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{
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static const uint64_t seed1[2] = {0x6572D100E85C2EFF,0xE85C2EFFFFFFFFFF}; // lfsr start values
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static const uint64_t seed2[2] = {0x05121100F8ECFEEF,0xF8ECFEEFEFEFEFEF}; // lfsr start values for single parity mode (1 == nbParityBits)
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const uint8_t m = 0xff >> (4 - nbParityBits);
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uint64_t r[2] = {(1 == nbParityBits)?seed2[0]:seed1[0],(1 == nbParityBits)?seed2[1]:seed1[1]};
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int i,j;
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for (i = 0; i < bitOfs;i++)
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{
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r[i & 1] = (r[i & 1] >> 8) | (((r[i & 1] >> 32) ^ (r[i & 1] >> 24) ^ (r[i & 1] >> 16) ^ r[i & 1]) << 56); // poly: 0x1D
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}
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for (j = 0; j < bufferSize; j++,i++)
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{
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buffer[j] ^= r[i & 1] & m;
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r[i & 1] = (r[i & 1] >> 8) | (((r[i & 1] >> 32) ^ (r[i & 1] >> 24) ^ (r[i & 1] >> 16) ^ r[i & 1]) << 56);
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}
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}
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/***********************************************************************
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* Decode 8 bits into a 4 bit word with single bit correction.
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* Non standard version used in sx1272.
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* Set error to true when a parity error was detected
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* Set bad to true when the result could not be corrected
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**********************************************************************/
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static inline unsigned char decodeHamming84sx(const unsigned char b, bool &error, bool &bad)
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{
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auto b0 = (b >> 0) & 0x1;
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auto b1 = (b >> 1) & 0x1;
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auto b2 = (b >> 2) & 0x1;
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auto b3 = (b >> 3) & 0x1;
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auto b4 = (b >> 4) & 0x1;
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auto b5 = (b >> 5) & 0x1;
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auto b6 = (b >> 6) & 0x1;
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auto b7 = (b >> 7) & 0x1;
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auto p0 = (b0 ^ b1 ^ b2 ^ b4);
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auto p1 = (b1 ^ b2 ^ b3 ^ b5);
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auto p2 = (b0 ^ b1 ^ b3 ^ b6);
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auto p3 = (b0 ^ b2 ^ b3 ^ b7);
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auto parity = (p0 << 0) | (p1 << 1) | (p2 << 2) | (p3 << 3);
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if (parity != 0) error = true;
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switch (parity & 0xf)
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{
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case 0xD: return (b ^ 1) & 0xf;
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case 0x7: return (b ^ 2) & 0xf;
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case 0xB: return (b ^ 4) & 0xf;
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case 0xE: return (b ^ 8) & 0xf;
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case 0x0:
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case 0x1:
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case 0x2:
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case 0x4:
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case 0x8: return b & 0xf;
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default: bad = true; return b & 0xf;
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}
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}
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/***********************************************************************
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* Simple 8-bit checksum routine
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**********************************************************************/
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static inline uint8_t checksum8(const uint8_t *p, const size_t len)
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{
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uint8_t acc = 0;
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for (size_t i = 0; i < len; i++)
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{
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acc = (acc >> 1) + ((acc & 0x1) << 7); //rotate
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acc += p[i]; //add
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}
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return acc;
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}
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static inline uint8_t headerChecksum(const uint8_t *h)
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{
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auto a0 = (h[0] >> 4) & 0x1;
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auto a1 = (h[0] >> 5) & 0x1;
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auto a2 = (h[0] >> 6) & 0x1;
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auto a3 = (h[0] >> 7) & 0x1;
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auto b0 = (h[0] >> 0) & 0x1;
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auto b1 = (h[0] >> 1) & 0x1;
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auto b2 = (h[0] >> 2) & 0x1;
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auto b3 = (h[0] >> 3) & 0x1;
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auto c0 = (h[1] >> 0) & 0x1;
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auto c1 = (h[1] >> 1) & 0x1;
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auto c2 = (h[1] >> 2) & 0x1;
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auto c3 = (h[1] >> 3) & 0x1;
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uint8_t res;
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res = (a0 ^ a1 ^ a2 ^ a3) << 4;
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res |= (a3 ^ b1 ^ b2 ^ b3 ^ c0) << 3;
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res |= (a2 ^ b0 ^ b3 ^ c1 ^ c3) << 2;
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res |= (a1 ^ b0 ^ b2 ^ c0 ^ c1 ^ c2) << 1;
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res |= a0 ^ b1 ^ c0 ^ c1 ^ c2 ^ c3;
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return res;
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}
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/***********************************************************************
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* Check parity for 5/4 code.
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* return true if parity is valid.
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**********************************************************************/
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static inline unsigned char checkParity54(const unsigned char b, bool &error)
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{
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auto x = b ^ (b >> 2);
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x = x ^ (x >> 1) ^ (b >> 4);
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if (x & 1) {
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error = true;
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}
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return b & 0xf;
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}
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/***********************************************************************
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* Check parity for 6/4 code.
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* return true if parity is valid.
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**********************************************************************/
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static inline unsigned char checkParity64(const unsigned char b, bool &error)
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{
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auto x = b ^ (b >> 1) ^ (b >> 2);
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auto y = x ^ b ^ (b >> 3);
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x ^= b >> 4;
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y ^= b >> 5;
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if ((x | y) & 1) {
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error = true;
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}
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return b & 0xf;
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}
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/***********************************************************************
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* Decode 7 bits into a 4 bit word with single bit correction.
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* Non standard version used in sx1272.
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* Set error to true when a parity error was detected
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* Non correctable errors are indistinguishable from single or no errors
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* therefore no 'bad' variable is proposed
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**********************************************************************/
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static inline unsigned char decodeHamming74sx(const unsigned char b, bool &error)
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{
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auto b0 = (b >> 0) & 0x1;
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auto b1 = (b >> 1) & 0x1;
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auto b2 = (b >> 2) & 0x1;
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auto b3 = (b >> 3) & 0x1;
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auto b4 = (b >> 4) & 0x1;
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auto b5 = (b >> 5) & 0x1;
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auto b6 = (b >> 6) & 0x1;
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auto p0 = (b0 ^ b1 ^ b2 ^ b4);
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auto p1 = (b1 ^ b2 ^ b3 ^ b5);
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auto p2 = (b0 ^ b1 ^ b3 ^ b6);
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auto parity = (p0 << 0) | (p1 << 1) | (p2 << 2);
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if (parity != 0) {
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error = true;
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}
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switch (parity)
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{
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case 0x5: return (b ^ 1) & 0xf;
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case 0x7: return (b ^ 2) & 0xf;
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case 0x3: return (b ^ 4) & 0xf;
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case 0x6: return (b ^ 8) & 0xf;
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case 0x0:
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case 0x1:
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case 0x2:
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case 0x4: break;
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}
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return b & 0xf;
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}
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/***********************************************************************
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* CRC reverse engineered from Sx1272 data stream.
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* Modified CCITT crc with masking of the output with an 8bit lfsr
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**********************************************************************/
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static inline uint16_t crc16sx(uint16_t crc, const uint16_t poly)
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{
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for (int i = 0; i < 8; i++)
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{
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if (crc & 0x8000) {
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crc = (crc << 1) ^ poly;
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} else {
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crc <<= 1;
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}
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}
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return crc;
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}
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static inline uint8_t xsum8(uint8_t t)
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{
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t ^= t >> 4;
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t ^= t >> 2;
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t ^= t >> 1;
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return (t & 1);
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}
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static inline uint16_t sx1272DataChecksum(const uint8_t *data, int length)
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{
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uint16_t res = 0;
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uint8_t v = 0xff;
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uint16_t crc = 0;
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for (int i = 0; i < length; i++)
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{
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crc = crc16sx(res, 0x1021);
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v = xsum8(v & 0xB8) | (v << 1);
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res = crc ^ data[i];
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}
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res ^= v;
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v = xsum8(v & 0xB8) | (v << 1);
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res ^= v << 8;
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return res;
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}
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};
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#endif // INCLUDE_CHIRPCHATDEMODDECODERLORA_H
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