mirror of
https://github.com/f4exb/sdrangel.git
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669 lines
22 KiB
C++
669 lines
22 KiB
C++
///////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2021-2022 Jon Beniston, M7RCE <jon@beniston.com> //
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// Copyright (C) 2021-2022 Edouard Griffiths, F4EXB <f4exb06@gmail.com> //
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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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#include <QDebug>
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#include <complex.h>
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#include "dsp/datafifo.h"
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#include "dsp/scopevis.h"
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#include "util/popcount.h"
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#include "maincore.h"
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#include "pagerdemod.h"
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#include "pagerdemodsink.h"
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PagerDemodSink::PagerDemodSink(PagerDemod *pagerDemod) :
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m_scopeSink(nullptr),
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m_pagerDemod(pagerDemod),
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m_channelSampleRate(PagerDemodSettings::m_channelSampleRate),
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m_channelFrequencyOffset(0),
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m_magsqSum(0.0f),
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m_magsqPeak(0.0f),
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m_magsqCount(0),
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m_messageQueueToChannel(nullptr),
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m_dcOffset(0.0f),
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m_dataPrev(0),
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m_inverted(false),
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m_bit(0),
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m_gotSOP(false),
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m_bits(0),
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m_bitCount(0),
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m_syncCount(75),
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m_batchNumber(0),
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m_wordCount(0),
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m_addressValid(0),
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m_sampleBufferIndex(0)
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{
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m_magsq = 0.0;
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m_demodBuffer.resize(1<<12);
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m_demodBufferFill = 0;
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applySettings(m_settings, true);
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applyChannelSettings(m_channelSampleRate, m_channelFrequencyOffset, true);
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m_sampleBuffer.resize(m_sampleBufferSize);
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}
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PagerDemodSink::~PagerDemodSink()
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{
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}
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void PagerDemodSink::sampleToScope(Complex sample)
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{
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if (m_scopeSink)
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{
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m_sampleBuffer[m_sampleBufferIndex++] = sample;
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if (m_sampleBufferIndex == m_sampleBufferSize)
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{
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std::vector<ComplexVector::const_iterator> vbegin;
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vbegin.push_back(m_sampleBuffer.begin());
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m_scopeSink->feed(vbegin, m_sampleBufferSize);
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m_sampleBufferIndex = 0;
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}
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}
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}
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void PagerDemodSink::feed(const SampleVector::const_iterator& begin, const SampleVector::const_iterator& end)
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{
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Complex ci;
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for (SampleVector::const_iterator it = begin; it != end; ++it)
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{
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Complex c(it->real(), it->imag());
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c *= m_nco.nextIQ();
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if (m_interpolatorDistance < 1.0f) // interpolate
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{
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while (!m_interpolator.interpolate(&m_interpolatorDistanceRemain, c, &ci))
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{
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processOneSample(ci);
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m_interpolatorDistanceRemain += m_interpolatorDistance;
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}
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}
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else // decimate
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{
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if (m_interpolator.decimate(&m_interpolatorDistanceRemain, c, &ci))
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{
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processOneSample(ci);
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m_interpolatorDistanceRemain += m_interpolatorDistance;
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}
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}
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}
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}
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// XOR bits together for parity check
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int PagerDemodSink::xorBits(quint32 word, int firstBit, int lastBit)
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{
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int x = 0;
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for (int i = firstBit; i <= lastBit; i++)
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{
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x ^= (word >> i) & 1;
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}
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return x;
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}
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// Check for even parity
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bool PagerDemodSink::evenParity(quint32 word, int firstBit, int lastBit, int parityBit)
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{
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return xorBits(word, firstBit, lastBit) == parityBit;
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}
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// Reverse order of bits
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quint32 PagerDemodSink::reverse(quint32 x)
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{
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x = (((x & 0xaaaaaaaa) >> 1) | ((x & 0x55555555) << 1));
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x = (((x & 0xcccccccc) >> 2) | ((x & 0x33333333) << 2));
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x = (((x & 0xf0f0f0f0) >> 4) | ((x & 0x0f0f0f0f) << 4));
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x = (((x & 0xff00ff00) >> 8) | ((x & 0x00ff00ff) << 8));
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return((x >> 16) | (x << 16));
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}
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// Calculate BCH parity and even parity bits
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quint32 PagerDemodSink::bchEncode(const quint32 cw)
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{
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quint32 bit = 0;
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quint32 localCW = cw & 0xFFFFF800; // Mask off BCH parity and even parity bits
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quint32 cwE = localCW;
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// Calculate BCH bits
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for (bit = 1; bit <= 21; bit++)
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{
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if (cwE & 0x80000000) {
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cwE ^= 0xED200000;
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}
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cwE <<= 1;
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}
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localCW |= (cwE >> 21);
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return localCW;
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}
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// Use BCH decoding to try to fix any bit errors
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// Returns true if able to be decode/repair successfull
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// See: https://www.eevblog.com/forum/microcontrollers/practical-guides-to-bch-fec/
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bool PagerDemodSink::bchDecode(const quint32 cw, quint32& correctedCW)
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{
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// Calculate syndrome
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// We do this by recalculating the BCH parity bits and XORing them against the received ones
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quint32 syndrome = ((bchEncode(cw) ^ cw) >> 1) & 0x3FF;
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if (syndrome == 0)
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{
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// Syndrome of zero indicates no repair required
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correctedCW = cw;
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return true;
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}
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// Meggitt decoder
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quint32 result = 0;
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quint32 damagedCW = cw;
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// Calculate BCH bits
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for (quint32 xbit = 0; xbit < 31; xbit++)
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{
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// Produce the next corrected bit in the high bit of the result
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result <<= 1;
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if ((syndrome == 0x3B4) || // 0x3B4: Syndrome when a single error is detected in the MSB
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(syndrome == 0x26E) || // 0x26E: Two adjacent errors
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(syndrome == 0x359) || // 0x359: Two errors, one OK bit between
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(syndrome == 0x076) || // 0x076: Two errors, two OK bits between
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(syndrome == 0x255) || // 0x255: Two errors, three OK bits between
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(syndrome == 0x0F0) || // 0x0F0: Two errors, four OK bits between
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(syndrome == 0x216) ||
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(syndrome == 0x365) ||
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(syndrome == 0x068) ||
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(syndrome == 0x25A) ||
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(syndrome == 0x343) ||
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(syndrome == 0x07B) ||
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(syndrome == 0x1E7) ||
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(syndrome == 0x129) ||
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(syndrome == 0x14E) ||
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(syndrome == 0x2C9) ||
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(syndrome == 0x0BE) ||
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(syndrome == 0x231) ||
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(syndrome == 0x0C2) ||
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(syndrome == 0x20F) ||
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(syndrome == 0x0DD) ||
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(syndrome == 0x1B4) ||
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(syndrome == 0x2B4) ||
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(syndrome == 0x334) ||
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(syndrome == 0x3F4) ||
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(syndrome == 0x394) ||
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(syndrome == 0x3A4) ||
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(syndrome == 0x3BC) ||
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(syndrome == 0x3B0) ||
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(syndrome == 0x3B6) ||
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(syndrome == 0x3B5)
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)
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{
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// Syndrome matches an error in the MSB
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// Correct that error and adjust the syndrome to account for it
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syndrome ^= 0x3B4;
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result |= (~damagedCW & 0x80000000) >> 30;
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}
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else
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{
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// No error
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result |= (damagedCW & 0x80000000) >> 30;
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}
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damagedCW <<= 1;
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// Handle syndrome shift register feedback
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if (syndrome & 0x200)
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{
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syndrome <<= 1;
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syndrome ^= 0x769; // 0x769 = POCSAG generator polynomial -- x^10 + x^9 + x^8 + x^6 + x^5 + x^3 + 1
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}
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else
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{
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syndrome <<= 1;
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}
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// Mask off bits which fall off the end of the syndrome shift register
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syndrome &= 0x3FF;
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}
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// Check if error correction was successful
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if (syndrome != 0)
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{
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// Syndrome nonzero at end indicates uncorrectable errors
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correctedCW = cw;
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return false;
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}
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correctedCW = result;
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return true;
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}
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// Decode a batch of codewords to addresses and messages
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// Messages may be spreadout over multiple batches
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// https://www.itu.int/dms_pubrec/itu-r/rec/m/R-REC-M.584-1-198607-S!!PDF-E.pdf
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// https://www.itu.int/dms_pubrec/itu-r/rec/m/R-REC-M.584-2-199711-I!!PDF-E.pdf
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void PagerDemodSink::decodeBatch()
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{
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int i = 1;
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for (int frame = 0; frame < PAGERDEMOD_FRAMES_PER_BATCH; frame++)
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{
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for (int word = 0; word < PAGERDEMOD_CODEWORDS_PER_FRAME; word++)
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{
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bool addressCodeWord = ((m_codeWords[i] >> 31) & 1) == 0;
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// Stop decoding current message if we receive a new address
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if (addressCodeWord && m_addressValid)
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{
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m_numericMessage = m_numericMessage.trimmed(); // Remove trailing spaces
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if (getMessageQueueToChannel())
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{
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// Convert from 7-bit to UTF-8 using user specified encoding
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for (int i = 0; i < m_alphaMessage.size(); i++)
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{
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QChar c = m_alphaMessage[i];
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int idx = m_settings.m_sevenbit.indexOf(c.toLatin1());
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if (idx >= 0) {
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c = QChar(m_settings.m_unicode[idx]);
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}
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m_alphaMessage[i] = c;
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}
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// Reverse reading order, if required
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if (m_settings.m_reverse) {
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std::reverse(m_alphaMessage.begin(), m_alphaMessage.end());
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}
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// Send to channel and GUI
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PagerDemod::MsgPagerMessage *msg = PagerDemod::MsgPagerMessage::create(m_address, m_functionBits, m_alphaMessage, m_numericMessage, m_parityErrors, m_bchErrors);
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getMessageQueueToChannel()->push(msg);
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}
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m_addressValid = false;
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}
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// Check parity bit
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bool parityError = !evenParity(m_codeWords[i], 1, 31, m_codeWords[i] & 0x1);
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if (m_codeWords[i] == PAGERDEMOD_POCSAG_IDLECODE)
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{
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// Idle
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}
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else if (addressCodeWord)
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{
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// Address
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m_functionBits = (m_codeWords[i] >> 11) & 0x3;
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int addressBits = (m_codeWords[i] >> 13) & 0x3ffff;
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m_address = (addressBits << 3) | frame;
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m_numericMessage = "";
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m_alphaMessage = "";
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m_alphaBitBufferBits = 0;
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m_alphaBitBuffer = 0;
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m_parityErrors = parityError ? 1 : 0;
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m_bchErrors = m_codeWordsBCHError[i] ? 1 : 0;
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m_addressValid = true;
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}
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else
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{
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// Message - decode as both numeric and ASCII - not all operators use functionBits to indidcate encoding
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int messageBits = (m_codeWords[i] >> 11) & 0xfffff;
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if (parityError) {
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m_parityErrors++;
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}
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if (m_codeWordsBCHError[i]) {
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m_bchErrors++;
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}
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// Numeric format
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for (int j = 16; j >= 0; j -= 4)
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{
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quint32 numericBits = (messageBits >> j) & 0xf;
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numericBits = reverse(numericBits) >> (32-4);
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// Spec has 0xa as 'spare', but other decoders treat is as .
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const char numericChars[] = {
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'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '.', 'U', ' ', '-', ')', '('
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};
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char numericChar = numericChars[numericBits];
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m_numericMessage.append(numericChar);
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}
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// 7-bit ASCII alpnanumeric format
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m_alphaBitBuffer = (m_alphaBitBuffer << 20) | messageBits;
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m_alphaBitBufferBits += 20;
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while (m_alphaBitBufferBits >= 7)
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{
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// Extract next 7-bit character from bit buffer
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char c = (m_alphaBitBuffer >> (m_alphaBitBufferBits-7)) & 0x7f;
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// Reverse bit ordering
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c = reverse(c) >> (32-7);
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// Add to received message string (excluding, null, end of text, end ot transmission)
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if (c != 0 && c != 0x3 && c != 0x4) {
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m_alphaMessage.append(c);
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}
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// Remove from bit buffer
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m_alphaBitBufferBits -= 7;
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if (m_alphaBitBufferBits == 0) {
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m_alphaBitBuffer = 0;
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} else {
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m_alphaBitBuffer &= (1 << m_alphaBitBufferBits) - 1;
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}
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}
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}
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// Move to next codeword
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i++;
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}
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}
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}
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void PagerDemodSink::processOneSample(Complex &ci)
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{
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// FM demodulation
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double magsqRaw;
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Real deviation;
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Real fmDemod = m_phaseDiscri.phaseDiscriminatorDelta(ci, magsqRaw, deviation);
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// Calculate average and peak levels for level meter
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Real magsq = magsqRaw / (SDR_RX_SCALED*SDR_RX_SCALED);
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m_movingAverage(magsq);
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m_magsq = m_movingAverage.asDouble();
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m_magsqSum += magsq;
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if (magsq > m_magsqPeak) {
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m_magsqPeak = magsq;
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}
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m_magsqCount++;
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// Low pass filter
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Real filt = m_lowpassBaud.filter(fmDemod);
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// An input frequency offset corresponds to a DC offset after FM demodulation
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// To calculate what it is, we average part of the preamble, which should be zero
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if (!m_gotSOP)
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{
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m_preambleMovingAverage(filt);
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m_dcOffset = m_preambleMovingAverage.asDouble();
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}
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bool sample = false;
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// Slice data
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int data = (filt - m_dcOffset) >= 0.0;
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// Look for edge - A PLL here would be less susceptible to noise
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if (data != m_dataPrev)
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{
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// Center in middle of bit
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m_syncCount = m_samplesPerSymbol/2;
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}
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else
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{
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// Wait until centre of bit to sample it
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m_syncCount--;
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if (m_syncCount <= 0)
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{
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// According to a variety of places on the web, high frequency is a 0, low is 1.
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// While this seems to be correct in the UK, some IQ files I've obtained seem
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// to be reversed, so we support both.
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if (m_inverted) {
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m_bit = data;
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} else {
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m_bit = !data;
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}
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sample = true;
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// Store in shift reg. MSB transmitted first
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m_bits = (m_bits << 1) | m_bit;
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m_bitCount++;
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if (m_bitCount > 32) {
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m_bitCount = 32;
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}
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if ((m_bitCount == 32) && !m_gotSOP)
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{
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// Look for synccode that starts a batch - allow three errors that can be corrected
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if (m_bits == PAGERDEMOD_POCSAG_SYNCCODE)
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{
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m_gotSOP = true;
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m_inverted = false;
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}
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else if (m_bits == PAGERDEMOD_POCSAG_SYNCCODE_INV)
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{
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m_gotSOP = true;
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m_inverted = true;
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}
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else if (popcount(m_bits ^ PAGERDEMOD_POCSAG_SYNCCODE) >= 29)
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{
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quint32 correctedCW;
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if (bchDecode(m_bits, correctedCW) && (correctedCW == PAGERDEMOD_POCSAG_SYNCCODE))
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{
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m_gotSOP = true;
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m_inverted = false;
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}
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}
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else if (popcount(m_bits ^ PAGERDEMOD_POCSAG_SYNCCODE_INV) >= 29)
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{
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quint32 correctedCW;
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if (bchDecode(~m_bits, correctedCW) && (correctedCW == PAGERDEMOD_POCSAG_SYNCCODE))
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{
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m_gotSOP = true;
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m_inverted = true;
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}
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}
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if (m_gotSOP)
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{
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// Reset demod state
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m_bits = 0;
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m_bitCount = 0;
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m_codeWords[0] = PAGERDEMOD_POCSAG_SYNCCODE;
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m_wordCount = 1;
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m_addressValid = false;
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}
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}
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else if ((m_bitCount == 32) && m_gotSOP)
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{
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// Got a complete codeword - use BCH decoding to fix any bit errors
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quint32 correctedCW;
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m_codeWordsBCHError[m_wordCount] = !bchDecode(m_bits, correctedCW);
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m_codeWords[m_wordCount] = correctedCW;
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m_wordCount++;
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// Check for sync code at start of batch
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if ((m_wordCount == 1) && (correctedCW != PAGERDEMOD_POCSAG_SYNCCODE))
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{
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m_gotSOP = false;
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//m_thresholdMet = false;
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m_addressValid = false;
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|
m_inverted = false;
|
|
}
|
|
|
|
// Have we received a complete batch
|
|
if (m_wordCount == PAGERDEMOD_BATCH_WORDS)
|
|
{
|
|
// Decode it to addresses and messages
|
|
decodeBatch();
|
|
|
|
// Start a new batch
|
|
m_batchNumber++;
|
|
m_wordCount = 0;
|
|
}
|
|
|
|
m_bits = 0;
|
|
m_bitCount = 0;
|
|
}
|
|
|
|
m_syncCount = m_samplesPerSymbol;
|
|
}
|
|
}
|
|
|
|
// Save data for edge detection
|
|
m_dataPrev = data;
|
|
// Select signals to feed to scope
|
|
Complex scopeSample;
|
|
|
|
switch (m_settings.m_scopeCh1)
|
|
{
|
|
case 0:
|
|
scopeSample.real(ci.real() / SDR_RX_SCALEF);
|
|
break;
|
|
case 1:
|
|
scopeSample.real(ci.imag() / SDR_RX_SCALEF);
|
|
break;
|
|
case 2:
|
|
scopeSample.real(magsq);
|
|
break;
|
|
case 3:
|
|
scopeSample.real(fmDemod);
|
|
break;
|
|
case 4:
|
|
scopeSample.real(filt);
|
|
break;
|
|
case 5:
|
|
scopeSample.real(m_dcOffset);
|
|
break;
|
|
case 6:
|
|
scopeSample.real(data);
|
|
break;
|
|
case 7:
|
|
scopeSample.real(sample);
|
|
break;
|
|
case 8:
|
|
scopeSample.real(m_bit);
|
|
break;
|
|
case 9:
|
|
scopeSample.real(m_gotSOP);
|
|
break;
|
|
}
|
|
|
|
switch (m_settings.m_scopeCh2)
|
|
{
|
|
case 0:
|
|
scopeSample.imag(ci.real() / SDR_RX_SCALEF);
|
|
break;
|
|
case 1:
|
|
scopeSample.imag(ci.imag() / SDR_RX_SCALEF);
|
|
break;
|
|
case 2:
|
|
scopeSample.imag(magsq);
|
|
break;
|
|
case 3:
|
|
scopeSample.imag(fmDemod);
|
|
break;
|
|
case 4:
|
|
scopeSample.imag(filt);
|
|
break;
|
|
case 5:
|
|
scopeSample.imag(m_dcOffset);
|
|
break;
|
|
case 6:
|
|
scopeSample.imag(data);
|
|
break;
|
|
case 7:
|
|
scopeSample.imag(sample);
|
|
break;
|
|
case 8:
|
|
scopeSample.imag(m_bit);
|
|
break;
|
|
case 9:
|
|
scopeSample.imag(m_gotSOP);
|
|
break;
|
|
}
|
|
|
|
sampleToScope(scopeSample);
|
|
|
|
// Send demod signal to Demod Analzyer feature
|
|
m_demodBuffer[m_demodBufferFill++] = fmDemod * std::numeric_limits<int16_t>::max();
|
|
|
|
if (m_demodBufferFill >= m_demodBuffer.size())
|
|
{
|
|
QList<ObjectPipe*> dataPipes;
|
|
MainCore::instance()->getDataPipes().getDataPipes(m_channel, "demod", dataPipes);
|
|
|
|
if (dataPipes.size() > 0)
|
|
{
|
|
QList<ObjectPipe*>::iterator it = dataPipes.begin();
|
|
|
|
for (; it != dataPipes.end(); ++it)
|
|
{
|
|
DataFifo *fifo = qobject_cast<DataFifo*>((*it)->m_element);
|
|
|
|
if (fifo) {
|
|
fifo->write((quint8*) &m_demodBuffer[0], m_demodBuffer.size() * sizeof(qint16), DataFifo::DataTypeI16);
|
|
}
|
|
}
|
|
}
|
|
|
|
m_demodBufferFill = 0;
|
|
}
|
|
}
|
|
|
|
void PagerDemodSink::applyChannelSettings(int channelSampleRate, int channelFrequencyOffset, bool force)
|
|
{
|
|
qDebug() << "PagerDemodSink::applyChannelSettings:"
|
|
<< " channelSampleRate: " << channelSampleRate
|
|
<< " channelFrequencyOffset: " << channelFrequencyOffset;
|
|
|
|
if ((m_channelFrequencyOffset != channelFrequencyOffset) ||
|
|
(m_channelSampleRate != channelSampleRate) || force)
|
|
{
|
|
m_nco.setFreq(-channelFrequencyOffset, channelSampleRate);
|
|
}
|
|
|
|
if ((m_channelSampleRate != channelSampleRate) || force)
|
|
{
|
|
m_interpolator.create(16, channelSampleRate, m_settings.m_rfBandwidth / 2.2);
|
|
m_interpolatorDistance = (Real) channelSampleRate / (Real) PagerDemodSettings::m_channelSampleRate;
|
|
m_interpolatorDistanceRemain = m_interpolatorDistance;
|
|
}
|
|
|
|
m_channelSampleRate = channelSampleRate;
|
|
m_channelFrequencyOffset = channelFrequencyOffset;
|
|
}
|
|
|
|
void PagerDemodSink::applySettings(const PagerDemodSettings& settings, bool force)
|
|
{
|
|
qDebug() << "PagerDemodSink::applySettings:"
|
|
<< " rfBandwidth: " << settings.m_rfBandwidth
|
|
<< " fmDeviation: " << settings.m_fmDeviation
|
|
<< " baud: " << settings.m_baud
|
|
<< " force: " << force;
|
|
|
|
if ((settings.m_rfBandwidth != m_settings.m_rfBandwidth) || force)
|
|
{
|
|
m_interpolator.create(16, m_channelSampleRate, settings.m_rfBandwidth / 2.2);
|
|
m_interpolatorDistance = (Real) m_channelSampleRate / (Real) PagerDemodSettings::m_channelSampleRate;
|
|
m_interpolatorDistanceRemain = m_interpolatorDistance;
|
|
m_lowpass.create(301, PagerDemodSettings::m_channelSampleRate, settings.m_rfBandwidth / 2.0f);
|
|
}
|
|
|
|
if ((settings.m_fmDeviation != m_settings.m_fmDeviation) || force)
|
|
{
|
|
m_phaseDiscri.setFMScaling(PagerDemodSettings::m_channelSampleRate / (2.0f * settings.m_fmDeviation));
|
|
}
|
|
|
|
if ((settings.m_baud != m_settings.m_baud) || force)
|
|
{
|
|
m_samplesPerSymbol = PagerDemodSettings::m_channelSampleRate / settings.m_baud;
|
|
qDebug() << "PagerDemodSink::applySettings: m_samplesPerSymbol: " << m_samplesPerSymbol;
|
|
|
|
// Signal is a square wave - so include several harmonics
|
|
m_lowpassBaud.create(301, PagerDemodSettings::m_channelSampleRate, settings.m_baud * 5.0f);
|
|
}
|
|
|
|
m_settings = settings;
|
|
}
|