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sdrangel/plugins/channelrx/demodpager/pagerdemodsink.cpp
DreamNik d2e89b7337 Fix PR comments
2024-09-09 19:17:30 +03:00

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