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sdrangel/plugins/channeltx/modnfm/nfmmoddcs.cpp

98 lines
3.9 KiB
C++

///////////////////////////////////////////////////////////////////////////////////
// Copyright (C) 2021 Edouard Griffiths, F4EXB <f4exb06@gmail.com> //
// //
// 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 as 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 V3 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/>. //
// //
// Source: https://mmi-comm.tripod.com/dcs.html //
///////////////////////////////////////////////////////////////////////////////////
#include <bitset>
#include "nfmmoddcs.h"
const float NFMModDCS::m_codeRate = 134.3; //!< bits per second
NFMModDCS::NFMModDCS()
{
reset();
}
NFMModDCS::~NFMModDCS()
{
}
void NFMModDCS::reset()
{
m_step = 0;
}
void NFMModDCS::setDCS(int code)
{
unsigned int dcsCode = code < 0 ? 0 : code > 511 ? 511 : code; // trim invalid values
// Parity bits calculation:
unsigned int p[11];
p[0] = std::bitset<32>(dcsCode & 0b10011111).count() % 2; // P0 = C0 + C1 + C2 + C3 + C4 + C7 (modulo two addition)
p[1] = (std::bitset<32>(dcsCode & 0b100111110).count()+1) % 2; // P1 = NOT ( C1 + C2 + C3 + C4 + C5 + C8 )
p[2] = std::bitset<32>(dcsCode & 0b11100011).count() % 2; // P2 = C0 + C1 + C5 + C6 + C7
p[3] = (std::bitset<32>(dcsCode & 0b111000110).count()+1) % 2; // P3 = NOT ( C1 + C2 + C6 + C7 + C8 )
p[4] = (std::bitset<32>(dcsCode & 0b100010011).count()+1) % 2; // P4 = NOT ( C0 + C1 + C4 + C8 )
p[5] = (std::bitset<32>(dcsCode & 0b10111001).count()+1) % 2; // P5 = NOT ( C0 + C3 + C4 + C5 + C7 )
p[6] = std::bitset<32>(dcsCode & 0b111101101).count() % 2; // P6 = C0 + C2 + C3 + C5 + C6 + C7 + C8
p[7] = std::bitset<32>(dcsCode & 0b111011010).count() % 2; // P7 = C1 + C3 + C4 + C6 + C7 + C8
p[8] = std::bitset<32>(dcsCode & 0b110110100).count() % 2; // P8 = C2 + C4 + C5 + C7 + C8
p[9] = (std::bitset<32>(dcsCode & 0b101101000).count()+1) % 2; // P9 = NOT ( C3 + C5 + C6 + C8 )
p[10] = (std::bitset<32>(dcsCode & 0b1001111).count()+1) % 2; // P10 = NOT ( C0 + C1 + C2 + C3 + C6 )
int dcsIndex = 0;
// code:
for (int i = 0; i < 9; i++, dcsIndex++) {
m_dcsWord[dcsIndex] = (dcsCode >> i) & 1;
}
// filler (0x04)
m_dcsWord[dcsIndex++] = 0;
m_dcsWord[dcsIndex++] = 0;
m_dcsWord[dcsIndex++] = 1;
// parity
for (int i = 0; i < 11; i++, dcsIndex++) {
m_dcsWord[dcsIndex] = p[i];
}
m_step = 0;
}
void NFMModDCS::setPositive(bool positive)
{
m_positive = positive;
m_step = 0;
}
void NFMModDCS::setSampleRate(int sampleRate)
{
m_bitPerStep = m_codeRate / sampleRate;
m_step = 0;
}
int NFMModDCS::next()
{
int dcsIndex = (int) m_step;
int carrier = (m_dcsWord[dcsIndex] == 1) ? (m_positive ? 1 : -1) : (m_positive ? -1 : 1);
if (m_step + m_bitPerStep < 23) {
m_step += m_bitPerStep;
} else {
m_step = m_step + m_bitPerStep - 23;
}
return carrier;
}