mayhem-firmware/firmware/baseband/proc_pocsag.cpp

/*
 * Copyright (C) 1996 Thomas Sailer (sailer@ife.ee.ethz.ch, hb9jnx@hb9w.che.eu)
 * Copyright (C) 2012-2014 Elias Oenal (multimon-ng@eliasoenal.com)
 * Copyright (C) 2015 Jared Boone, ShareBrained Technology, Inc.
 * Copyright (C) 2016 Furrtek
 *
 * This file is part of PortaPack.
 *
 * 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, 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; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

#include "proc_pocsag.hpp"

#include "event_m4.hpp"

#include <cstdint>
#include <cstddef>
#include <algorithm>  // std::max
#include <cmath>

void POCSAGProcessor::execute(const buffer_c8_t& buffer) {
    // This is called at 1500Hz

    if (!configured) return;

    // Get 24kHz audio
    const auto decim_0_out = decim_0.execute(buffer, dst_buffer);
    const auto decim_1_out = decim_1.execute(decim_0_out, dst_buffer);
    const auto channel_out = channel_filter.execute(decim_1_out, dst_buffer);
    auto audio = demod.execute(channel_out, audio_buffer);
    smooth.Process(audio.p, audio.count);  // Smooth the data to  make decoding more accurate
    audio_output.write(audio);

    processDemodulatedSamples(audio.p, 16);
    extractFrames();
}

// ====================================================================
//
// ====================================================================
int POCSAGProcessor::OnDataWord(uint32_t word, int pos) {
    packet.set(pos, word);
    return 0;
}

// ====================================================================
//
// ====================================================================
int POCSAGProcessor::OnDataFrame(int len, int baud) {
    if (len > 0) {
        packet.set_bitrate(baud);
        packet.set_flag(pocsag::PacketFlag::NORMAL);
        packet.set_timestamp(Timestamp::now());
        const POCSAGPacketMessage message(packet);
        shared_memory.application_queue.push(message);
    }
    return 0;
}

void POCSAGProcessor::on_message(const Message* const message) {
    if (message->id == Message::ID::POCSAGConfigure)
        configure();
}

void POCSAGProcessor::configure() {
    constexpr size_t decim_0_input_fs = baseband_fs;
    constexpr size_t decim_0_output_fs = decim_0_input_fs / decim_0.decimation_factor;

    constexpr size_t decim_1_input_fs = decim_0_output_fs;
    constexpr size_t decim_1_output_fs = decim_1_input_fs / decim_1.decimation_factor;

    constexpr size_t channel_filter_input_fs = decim_1_output_fs;
    const size_t channel_filter_output_fs = channel_filter_input_fs / 2;

    const size_t demod_input_fs = channel_filter_output_fs;

    decim_0.configure(taps_11k0_decim_0.taps, 33554432);
    decim_1.configure(taps_11k0_decim_1.taps, 131072);
    channel_filter.configure(taps_11k0_channel.taps, 2);
    demod.configure(demod_input_fs, 4500);
    // Smoothing should be roughly sample rate over max baud
    // 24k / 3.2k is 7.5
    smooth.SetSize(8);
    audio_output.configure(false);

    // Set up the frame extraction, limits of baud
    setFrameExtractParams(demod_input_fs, 4000, 300, 32);

    // Mark the class as ready to accept data
    configured = true;
}

// -----------------------------
// Frame extractraction methods
// -----------------------------
#define BAUD_STABLE (104)
#define MAX_CONSEC_SAME (32)
#define MAX_WITHOUT_SINGLE (64)
#define MAX_BAD_TRANS (10)

#define M_SYNC (0x7cd215d8)
#define M_NOTSYNC (0x832dea27)

#define M_IDLE (0x7a89c197)

// ====================================================================
//
// ====================================================================
inline int bitsDiff(unsigned long left, unsigned long right) {
    unsigned long xord = left ^ right;
    int count = 0;
    for (int i = 0; i < 32; i++) {
        if ((xord & 0x01) != 0) ++count;
        xord = xord >> 1;
    }
    return (count);
}

// ====================================================================
//
// ====================================================================
void POCSAGProcessor::initFrameExtraction() {
    m_averageSymbolLen_1024 = m_maxSymSamples_1024;
    m_lastStableSymbolLen_1024 = m_minSymSamples_1024;

    m_badTransitions = 0;
    m_bitsStart = 0;
    m_bitsEnd = 0;
    m_inverted = false;

    resetVals();
}

// ====================================================================
//
// ====================================================================
void POCSAGProcessor::resetVals() {
    // Reset the parameters
    // --------------------
    m_goodTransitions = 0;
    m_badTransitions = 0;
    m_averageSymbolLen_1024 = m_maxSymSamples_1024;
    m_shortestGoodTrans_1024 = m_maxSymSamples_1024;
    m_valMid = 0;

    // And reset the counts
    // --------------------
    m_lastTransPos_1024 = 0;
    m_lastBitPos_1024 = 0;
    m_lastSample = 0;
    m_sampleNo = 0;
    m_nextBitPos_1024 = m_maxSymSamples_1024;
    m_nextBitPosInt = (long)m_nextBitPos_1024;

    // Extraction
    m_fifo.numBits = 0;
    m_gotSync = false;
    m_numCode = 0;
}

// ====================================================================
//
// ====================================================================
void POCSAGProcessor::setFrameExtractParams(long a_samplesPerSec, long a_maxBaud, long a_minBaud, long maxRunOfSameValue) {
    m_samplesPerSec = a_samplesPerSec;
    m_minSymSamples_1024 = (uint32_t)(1024.0f * (float)a_samplesPerSec / (float)a_maxBaud);
    m_maxSymSamples_1024 = (uint32_t)(1024.0f * (float)a_samplesPerSec / (float)a_minBaud);
    m_maxRunOfSameValue = maxRunOfSameValue;

    m_shortestGoodTrans_1024 = m_maxSymSamples_1024;
    m_averageSymbolLen_1024 = m_maxSymSamples_1024;
    m_lastStableSymbolLen_1024 = m_minSymSamples_1024;

    m_nextBitPos_1024 = m_averageSymbolLen_1024 / 2;
    m_nextBitPosInt = m_nextBitPos_1024 >> 10;

    initFrameExtraction();
}

// ====================================================================
//
// ====================================================================
int POCSAGProcessor::processDemodulatedSamples(float* sampleBuff, int noOfSamples) {
    bool transition = false;
    uint32_t samplePos_1024 = 0;
    uint32_t len_1024 = 0;

    // Loop through the block of data
    // ------------------------------
    for (int pos = 0; pos < noOfSamples; ++pos) {
        m_sample = sampleBuff[pos];
        m_valMid += (m_sample - m_valMid) / 1024.0f;

        ++m_sampleNo;

        // Detect Transition
        // -----------------
        transition = !((m_lastSample < m_valMid) ^ (m_sample >= m_valMid));  // use XOR for speed

        // If this is a transition
        // -----------------------
        if (transition) {
            // Calculate samples since last trans
            // ----------------------------------
            int32_t fractional_1024 = (int32_t)(((m_sample - m_valMid) * 1024) / (m_sample - m_lastSample));
            if (fractional_1024 < 0) {
                fractional_1024 = -fractional_1024;
            }

            samplePos_1024 = (m_sampleNo << 10) - fractional_1024;
            len_1024 = samplePos_1024 - m_lastTransPos_1024;
            m_lastTransPos_1024 = samplePos_1024;

            // If symbol is large enough to be valid
            // -------------------------------------
            if (len_1024 > m_minSymSamples_1024) {
                // Check for shortest good transition
                // ----------------------------------
                if ((len_1024 < m_shortestGoodTrans_1024) &&
                    (m_goodTransitions < BAUD_STABLE))  // detect change of symbol size
                {
                    int32_t fractionOfShortest_1024 = (len_1024 << 10) / m_shortestGoodTrans_1024;

                    // If currently at half the baud rate
                    // ----------------------------------
                    if ((fractionOfShortest_1024 > 410) && (fractionOfShortest_1024 < 614))  // 0.4 and 0.6
                    {
                        m_averageSymbolLen_1024 /= 2;
                        m_shortestGoodTrans_1024 = len_1024;
                    }
                    // If currently at the wrong baud rate
                    // -----------------------------------
                    else if (fractionOfShortest_1024 < 768)  // 0.75
                    {
                        m_averageSymbolLen_1024 = len_1024;
                        m_shortestGoodTrans_1024 = len_1024;
                        m_goodTransitions = 0;
                        m_lastSingleBitPos_1024 = samplePos_1024 - len_1024;
                    }
                }

                // Calc the number of bits since events
                // ------------------------------------
                int32_t halfSymbol_1024 = m_averageSymbolLen_1024 / 2;
                int bitsSinceLastTrans = max((uint32_t)1, (len_1024 + halfSymbol_1024) / m_averageSymbolLen_1024);
                int bitsSinceLastSingle = (((m_sampleNo << 10) - m_lastSingleBitPos_1024) + halfSymbol_1024) / m_averageSymbolLen_1024;

                // Check for single bit
                // --------------------
                if (bitsSinceLastTrans == 1) {
                    m_lastSingleBitPos_1024 = samplePos_1024;
                }

                // If too long since last transition
                // ---------------------------------
                if (bitsSinceLastTrans > MAX_CONSEC_SAME) {
                    resetVals();
                }
                // If too long sice last single bit
                // --------------------------------
                else if (bitsSinceLastSingle > MAX_WITHOUT_SINGLE) {
                    resetVals();
                } else {
                    // If this is a good transition
                    // ----------------------------
                    int32_t offsetFromExtectedTransition_1024 = len_1024 - (bitsSinceLastTrans * m_averageSymbolLen_1024);
                    if (offsetFromExtectedTransition_1024 < 0) {
                        offsetFromExtectedTransition_1024 = -offsetFromExtectedTransition_1024;
                    }
                    if (offsetFromExtectedTransition_1024 < ((int32_t)m_averageSymbolLen_1024 / 4))  // Has to be within 1/4 of symbol to be good
                    {
                        ++m_goodTransitions;
                        uint32_t bitsCount = min((uint32_t)BAUD_STABLE, m_goodTransitions);

                        uint32_t propFromPrevious = m_averageSymbolLen_1024 * bitsCount;
                        uint32_t propFromCurrent = (len_1024 / bitsSinceLastTrans);
                        m_averageSymbolLen_1024 = (propFromPrevious + propFromCurrent) / (bitsCount + 1);
                        m_badTransitions = 0;
                        // if ( len < m_shortestGoodTrans ){m_shortestGoodTrans = len;}
                        //  Store the old symbol size
                        if (m_goodTransitions >= BAUD_STABLE) {
                            m_lastStableSymbolLen_1024 = m_averageSymbolLen_1024;
                        }
                    }
                }

                // Set the point of the last bit if not yet stable
                // -----------------------------------------------
                if ((m_goodTransitions < BAUD_STABLE) || (m_badTransitions > 0)) {
                    m_lastBitPos_1024 = samplePos_1024 - (m_averageSymbolLen_1024 / 2);
                }

                // Calculate the exact positiom of the next bit
                // --------------------------------------------
                int32_t thisPlusHalfsymbol_1024 = samplePos_1024 + (m_averageSymbolLen_1024 / 2);
                int32_t lastPlusSymbol = m_lastBitPos_1024 + m_averageSymbolLen_1024;
                m_nextBitPos_1024 = lastPlusSymbol + ((thisPlusHalfsymbol_1024 - lastPlusSymbol) / 16);

                // Check for bad pos error
                // -----------------------
                if (m_nextBitPos_1024 < samplePos_1024) m_nextBitPos_1024 += m_averageSymbolLen_1024;

                // Calculate integer sample after next bit
                // ---------------------------------------
                m_nextBitPosInt = (m_nextBitPos_1024 >> 10) + 1;

            }  // symbol is large enough to be valid
            else {
                // Bad transition, so reset the counts
                // -----------------------------------
                ++m_badTransitions;
                if (m_badTransitions > MAX_BAD_TRANS) {
                    resetVals();
                }
            }
        }  // end of if transition

        // Reached the point of the next bit
        // ---------------------------------
        if (m_sampleNo >= m_nextBitPosInt) {
            // Everything is good so extract a bit
            // -----------------------------------
            if (m_goodTransitions > 20) {
                // Store value at the center of bit
                // --------------------------------
                storeBit();
            }
            // Check for long 1 or zero
            // ------------------------
            uint32_t bitsSinceLastTrans = ((m_sampleNo << 10) - m_lastTransPos_1024) / m_averageSymbolLen_1024;
            if (bitsSinceLastTrans > m_maxRunOfSameValue) {
                resetVals();
            }

            // Store the point of the last bit
            // -------------------------------
            m_lastBitPos_1024 = m_nextBitPos_1024;

            // Calculate the exact point of the next bit
            // -----------------------------------------
            m_nextBitPos_1024 += m_averageSymbolLen_1024;

            // Look for the bit after the next bit pos
            // ---------------------------------------
            m_nextBitPosInt = (m_nextBitPos_1024 >> 10) + 1;

        }  // Reached the point of the next bit

        m_lastSample = m_sample;

    }  // Loop through the block of data

    return getNoOfBits();
}

// ====================================================================
//
// ====================================================================
void POCSAGProcessor::storeBit() {
    if (++m_bitsStart >= BIT_BUF_SIZE) {
        m_bitsStart = 0;
    }

    // Calculate the bit value
    float sample = (m_sample + m_lastSample) / 2;
    // int32_t sample_1024 = m_sample_1024;
    bool bit = sample > m_valMid;

    // If buffer not full
    if (m_bitsStart != m_bitsEnd) {
        // Decide on output val
        if (bit) {
            m_bits[m_bitsStart] = 0;
        } else {
            m_bits[m_bitsStart] = 1;
        }
    }
    // Throw away bits if the buffer is full
    else {
        if (--m_bitsStart <= -1) {
            m_bitsStart = BIT_BUF_SIZE - 1;
        }
    }
}

// ====================================================================
//
// ====================================================================
int POCSAGProcessor::extractFrames() {
    int msgCnt = 0;
    // While there is unread data in the bits buffer
    //----------------------------------------------
    while (getNoOfBits() > 0) {
        m_fifo.codeword = (m_fifo.codeword << 1) + getBit();
        m_fifo.numBits++;

        // If number of bits in fifo equals 32
        //------------------------------------
        if (m_fifo.numBits >= 32) {
            // Not got sync
            // ------------
            if (!m_gotSync) {
                if (bitsDiff(m_fifo.codeword, M_SYNC) <= 2) {
                    m_inverted = false;
                    m_gotSync = true;
                    m_numCode = -1;
                    m_fifo.numBits = 0;
                } else if (bitsDiff(m_fifo.codeword, M_NOTSYNC) <= 2) {
                    m_inverted = true;
                    m_gotSync = true;
                    m_numCode = -1;
                    m_fifo.numBits = 0;
                } else {
                    // Cause it to load one more bit
                    m_fifo.numBits = 31;
                }
            }  // Not got sync
            else {
                // Increment the word count
                // ------------------------
                ++m_numCode;  // It got set to -1 when a sync was found, now count the 16 words
                uint32_t val = m_inverted ? ~m_fifo.codeword : m_fifo.codeword;
                OnDataWord(val, m_numCode);

                // If at the end of a 16 word block
                // --------------------------------
                if (m_numCode >= 15) {
                    msgCnt += OnDataFrame(m_numCode + 1, (m_samplesPerSec << 10) / m_lastStableSymbolLen_1024);
                    m_gotSync = false;
                    m_numCode = -1;
                }
                m_fifo.numBits = 0;
            }
        }  // If number of bits in fifo equals 32
    }      // While there is unread data in the bits buffer
    return msgCnt;
}  // extractFrames

// ====================================================================
//
// ====================================================================
short POCSAGProcessor::getBit() {
    if (m_bitsEnd != m_bitsStart) {
        if (++m_bitsEnd >= BIT_BUF_SIZE) {
            m_bitsEnd = 0;
        }
        return m_bits[m_bitsEnd];
    } else {
        return -1;
    }
}

// ====================================================================
//
// ====================================================================
int POCSAGProcessor::getNoOfBits() {
    int bits = m_bitsEnd - m_bitsStart;
    if (bits < 0) {
        bits += BIT_BUF_SIZE;
    }
    return bits;
}

// ====================================================================
//
// ====================================================================
uint32_t POCSAGProcessor::getRate() {
    return ((m_samplesPerSec << 10) + 512) / m_lastStableSymbolLen_1024;
}

// ====================================================================
//
// ====================================================================
int main() {
    EventDispatcher event_dispatcher{std::make_unique<POCSAGProcessor>()};
    event_dispatcher.run();
    return 0;
}