m17-cxx-demod/m17-mod.cpp

// Copyright 2020 Mobilinkd LLC.

#include "Util.h"
#include "queue.h"
#include "FirFilter.h"
#include "LinkSetupFrame.h"
#include "CRC16.h"
#include "Trellis.h"
#include "Convolution.h"
#include "PolynomialInterleaver.h"
#include "M17Randomizer.h"
#include "Util.h"
#include "Golay24.h"

#include <codec2/codec2.h>

#include <boost/program_options.hpp>
#include <boost/optional.hpp>

#include <thread>

#include <array>
#include <experimental/array>
#include <iostream>
#include <iomanip>
#include <atomic>
#include <optional>

#include <cstdlib>

#include <signal.h>

// Generated using scikit-commpy
const auto rrc_taps = std::experimental::make_array<double>(
    -0.009265784007800534, -0.006136551625729697, -0.001125978562075172, 0.004891777252042491,
    0.01071805138282269, 0.01505751553351295, 0.01679337935001369, 0.015256245142156299,
    0.01042830577908502, 0.003031522725559901,  -0.0055333532968188165, -0.013403099825723372,
    -0.018598682349642525, -0.01944761739590459, -0.015005271935951746, -0.0053887880354343935,
    0.008056525910253532, 0.022816244158307273, 0.035513467692208076, 0.04244131815783876,
    0.04025481153629372, 0.02671818654865632, 0.0013810216516704976, -0.03394615682795165,
    -0.07502635967975885, -0.11540977897637611, -0.14703962203941534, -0.16119995609538576,
    -0.14969512896336504, -0.10610329539459686, -0.026921412469634916, 0.08757875030779196,
    0.23293327870303457, 0.4006012210123992, 0.5786324696325503, 0.7528286479934068,
    0.908262741447522, 1.0309661131633199, 1.1095611856548013, 1.1366197723675815,
    1.1095611856548013, 1.0309661131633199, 0.908262741447522, 0.7528286479934068,
    0.5786324696325503,  0.4006012210123992, 0.23293327870303457, 0.08757875030779196,
    -0.026921412469634916, -0.10610329539459686, -0.14969512896336504, -0.16119995609538576,
    -0.14703962203941534, -0.11540977897637611, -0.07502635967975885, -0.03394615682795165,
    0.0013810216516704976, 0.02671818654865632, 0.04025481153629372,  0.04244131815783876,
    0.035513467692208076, 0.022816244158307273, 0.008056525910253532, -0.0053887880354343935,
    -0.015005271935951746, -0.01944761739590459, -0.018598682349642525, -0.013403099825723372,
    -0.0055333532968188165, 0.003031522725559901, 0.01042830577908502, 0.015256245142156299,
    0.01679337935001369, 0.01505751553351295, 0.01071805138282269, 0.004891777252042491,
    -0.001125978562075172, -0.006136551625729697, -0.009265784007800534
);

const auto evm_b = std::experimental::make_array<double>(0.02008337, 0.04016673, 0.02008337);
const auto evm_a = std::experimental::make_array<double>(1.0, -1.56101808, 0.64135154);

const char VERSION[] = "1.0";

struct Config
{
    std::string source_address;
    std::string destination_address;
    std::string audio_device;
    std::string event_device;
    uint16_t key;
    bool verbose = false;
    bool debug = false;
    bool quiet = false;
    bool bitstream = false; // default is baseband audio

    static std::optional<Config> parse(int argc, char* argv[])
    {
        namespace po = boost::program_options;

        Config result;

        // Declare the supported options.
        po::options_description desc(
            "Program options");
        desc.add_options()
            ("help,h", "Print this help message and exit.")
            ("version,V", "Print the application verion and exit.")
            ("src,S", po::value<std::string>(&result.source_address)->required(),
                "transmitter identifier (your callsign).")
            ("dest,D", po::value<std::string>(&result.destination_address),
                "destination (default is broadcast).")
            ("audio,a", po::value<std::string>(&result.audio_device),
                "audio device (default is STDIN).")
            ("event,e", po::value<std::string>(&result.event_device)->default_value("/dev/input/by-id/usb-C-Media_Electronics_Inc._USB_Audio_Device-event-if03"),
                "event device (default is C-Media Electronics Inc. USB Audio Device).")
            ("key,k", po::value<uint16_t>(&result.key)->default_value(385),
                "Linux event code for PTT (default is RADIO).")
            ("bitstream,b", po::bool_switch(&result.bitstream),
                "output bitstream (default is baseband).")
            ("verbose,v", po::bool_switch(&result.verbose), "verbose output")
            ("debug,d", po::bool_switch(&result.debug), "debug-level output")
            ("quiet,q", po::bool_switch(&result.quiet), "silence all output")
            ;

        po::variables_map vm;
        po::store(po::parse_command_line(argc, argv, desc), vm);

        if (vm.count("help"))
        {
            std::cout << "Read audio from STDIN and write baseband M17 to STDOUT\n"
                << desc << std::endl;

            return std::nullopt;
        }

        if (vm.count("version"))
        {
            std::cout << argv[0] << ": " << VERSION << std::endl;
            return std::nullopt;
        }

        try {
            po::notify(vm);
        } catch (std::exception& ex)
        {
            std::cerr << ex.what() << std::endl;
            std::cout << desc << std::endl;
            return std::nullopt;
        }

        if (result.debug + result.verbose + result.quiet > 1)
        {
            std::cerr << "Only one of quiet, verbos or debug may be chosen." << std::endl;
            return std::nullopt;
        }

        if (result.source_address.size() > 9)
        {
            std::cerr << "Source identifier too long." << std::endl;
            return std::nullopt;
        }

        if (result.destination_address.size() > 9)
        {
            std::cerr << "Destination identifier too long." << std::endl;
            return std::nullopt;
        }

        return result;
    }
};

using lsf_t = std::array<uint8_t, 30>;

std::atomic<bool> running{true};

bool bitstream = false;

void signal_handler(int)
{
    running = false;
    std::cerr << "quitting" << std::endl;
}


int8_t bits_to_symbol(uint8_t bits)
{
    switch (bits)
    {
    case 0: return 1;
    case 1: return 3;
    case 2: return -1;
    case 3: return -3;
    }
    abort();
}

template <typename T, size_t N>
std::array<int8_t, N / 2> bits_to_symbols(const std::array<T, N>& bits)
{
    std::array<int8_t, N / 2> result;
    size_t index = 0;
    for (size_t i = 0; i != N; i += 2)
    {
        result[index++] = bits_to_symbol((bits[i] << 1) | bits[i + 1]);
    }
    return result;
}

template <typename T, size_t N>
std::array<int8_t, N * 4> bytes_to_symbols(const std::array<T, N>& bytes)
{
    std::array<int8_t, N * 4> result;
    size_t index = 0;
    for (auto b : bytes)
    {
        for (size_t i = 0; i != 4; ++i)
        {
            result[index++] = bits_to_symbol(b >> 6);
            b <<= 2;
        }
    }
    return result;
}

std::array<int16_t, 1920> symbols_to_baseband(std::array<int8_t, 192> symbols)
{
    using namespace mobilinkd;

    static BaseFirFilter<double, std::tuple_size<decltype(rrc_taps)>::value> rrc = makeFirFilter(rrc_taps);

    std::array<int16_t, 1920> baseband;
    baseband.fill(0);
    for (size_t i = 0; i != symbols.size(); ++i)
    {
        baseband[i * 10] = symbols[i];
    }

    for (auto& b : baseband)
    {
        b = rrc(b) * 25.0;
    }
    return baseband;
}


using bitstream_t = std::array<int8_t, 368>;

void output_bitstream(std::array<uint8_t, 2> sync_word, const bitstream_t& frame)
{
    for (auto c : sync_word) std::cout << c;
    for (size_t i = 0; i != frame.size(); i += 8)
    {
        uint8_t c = 0;
        for (size_t j = 0; j != 8; ++j)
        {
            c <<= 1;
            c |= frame[i + j];
        }
        std::cout << c;
    }
}

void output_baseband(std::array<uint8_t, 2> sync_word, const bitstream_t& frame)
{
    auto symbols = bits_to_symbols(frame);
    auto sw = bytes_to_symbols(sync_word);

    std::array<int8_t, 192> temp;
    auto fit = std::copy(sw.begin(), sw.end(), temp.begin());
    std::copy(symbols.begin(), symbols.end(), fit);
    auto baseband = symbols_to_baseband(temp);
    for (auto b : baseband) std::cout << uint8_t((b & 0xFF00) >> 8) << uint8_t(b & 0xFF);
}


void output_frame(std::array<uint8_t, 2> sync_word, const bitstream_t& frame)
{
    if (bitstream) output_bitstream(sync_word, frame);
    else output_baseband(sync_word, frame);
}

void send_preamble()
{
    // Preamble is simple... bytes -> symbols -> baseband.
    std::cerr << "Sending preamble." << std::endl;
    std::array<uint8_t, 48> preamble_bytes;
    preamble_bytes.fill(0x77);
    if (bitstream)
    {
        for (auto c : preamble_bytes) std::cout << c;
    }
    else // baseband
    {
        auto preamble_symbols = bytes_to_symbols(preamble_bytes);
        auto preamble_baseband = symbols_to_baseband(preamble_symbols);
        for (auto b : preamble_baseband) std::cout << uint8_t(b >> 8) << uint8_t(b & 0xFF);
    }
}

constexpr std::array<uint8_t, 2> SYNC_WORD = {0x32, 0x43};

lsf_t send_lsf(const std::string& src, const std::string& dest)
{
    using namespace mobilinkd;

    lsf_t result;
    result.fill(0);
    
    M17Randomizer<368> randomizer;
    PolynomialInterleaver<45, 92, 368> interleaver;
    CRC16<0x5935, 0xFFFF> crc;

    std::cerr << "Sending link setup." << std::endl;

    mobilinkd::LinkSetupFrame::call_t callsign;
    callsign.fill(0);
    std::copy(src.begin(), src.end(), callsign.begin());
    auto encoded_src = mobilinkd::LinkSetupFrame::encode_callsign(callsign);

     mobilinkd::LinkSetupFrame::encoded_call_t encoded_dest = {0xff,0xff,0xff,0xff,0xff,0xff};
     if (!dest.empty())
     {
        callsign.fill(0);
        std::copy(dest.begin(), dest.end(), callsign.begin());
        encoded_dest = mobilinkd::LinkSetupFrame::encode_callsign(callsign);
     }

    auto rit = std::copy(encoded_src.begin(), encoded_src.end(), result.begin());
    std::copy(encoded_dest.begin(), encoded_dest.end(), rit);
    result[12] = 0;
    result[13] = 5;

    crc.reset();
    for (size_t i = 0; i != 28; ++i)
    {
        crc(result[i]);
    }
    auto checksum = crc.get_bytes();
    result[28] = checksum[0];
    result[29] = checksum[1];

    std::array<uint8_t, 488> encoded;
    size_t index = 0;
    uint32_t memory = 0;
    for (auto b : result)
    {
        for (size_t i = 0; i != 8; ++i)
        {
            uint32_t x = (b & 0x80) >> 7;
            b <<= 1;
            memory = mobilinkd::update_memory<4>(memory, x);
            encoded[index++] = mobilinkd::convolve_bit(031, memory);
            encoded[index++] = mobilinkd::convolve_bit(027, memory);
        }
    }
    // Flush the encoder.
    for (size_t i = 0; i != 4; ++i)
    {
        memory = mobilinkd::update_memory<4>(memory, 0);
        encoded[index++] = mobilinkd::convolve_bit(031, memory);
        encoded[index++] = mobilinkd::convolve_bit(027, memory);
    }

    std::array<int8_t, 368> punctured;
    auto size = puncture(encoded, punctured, P1);
    assert(size == 368);

    interleaver.interleave(punctured);
    randomizer.randomize(punctured);
    output_frame(SYNC_WORD, punctured);

    return result;
}

using lich_segment_t = std::array<uint8_t, 96>;
using lich_t = std::array<lich_segment_t, 6>;
using queue_t = mobilinkd::queue<int16_t, 320>;
using audio_frame_t = std::array<int16_t, 320>;
using codec_frame_t = std::array<uint8_t, 16>;
using data_frame_t = std::array<int8_t, 272>;

/**
 * Encode 2 frames of data.  Caller must ensure that the audio is
 * padded with 0s if the incoming data is incomplete.
 */
codec_frame_t encode(struct CODEC2* codec2, const audio_frame_t& audio)
{
    codec_frame_t result;
    codec2_encode(codec2, &result[0], const_cast<int16_t*>(&audio[0]));
    codec2_encode(codec2, &result[8], const_cast<int16_t*>(&audio[160]));
    return result;
}

data_frame_t make_data_frame(uint16_t frame_number, const codec_frame_t& payload)
{
    std::array<uint8_t, 20> data;   // FN, Audio, CRC = 2 + 16 + 2;
    data[0] = uint8_t((frame_number >> 8) & 0xFF);
    data[1] = uint8_t(frame_number & 0xFF);
    std::copy(payload.begin(), payload.end(), data.begin() + 2);

    mobilinkd::CRC16<0x5935, 0xFFFF> crc;
    crc.reset();
    for (size_t i = 0; i != 18; ++i) crc(data[i]);
    auto checksum = crc.get_bytes();
    data[18] = checksum[0];
    data[19] = checksum[1];

    std::array<uint8_t, 328> encoded;
    size_t index = 0;
    uint32_t memory = 0;
    for (auto b : data)
    {
        for (size_t i = 0; i != 8; ++i)
        {
            uint32_t x = (b & 0x80) >> 7;
            b <<= 1;
            memory = mobilinkd::update_memory<4>(memory, x);
            encoded[index++] = mobilinkd::convolve_bit(031, memory);
            encoded[index++] = mobilinkd::convolve_bit(027, memory);
        }
    }
    // Flush the encoder.
    for (size_t i = 0; i != 4; ++i)
    {
        memory = mobilinkd::update_memory<4>(memory, 0);
        encoded[index++] = mobilinkd::convolve_bit(031, memory);
        encoded[index++] = mobilinkd::convolve_bit(027, memory);
    }

    data_frame_t punctured;
    auto size = mobilinkd::puncture(encoded, punctured, mobilinkd::P2);
    assert(size == 272);
    return punctured;
}

/**
 * Encode each LSF segment into a Golay-encoded LICH segment bitstream.
 */
lich_segment_t make_lich_segment(std::array<uint8_t, 5> segment, uint8_t segment_number)
{
    lich_segment_t result;
    uint16_t tmp;
    uint32_t encoded;

    tmp = segment[0] << 4 | ((segment[1] >> 4) & 0x0F);
    encoded = mobilinkd::Golay24::encode24(tmp);
    for (size_t i = 0; i != 24; ++i)
    {
        result[i] = (encoded & (1 << 23)) != 0;
        encoded <<= 1;
    }

    tmp = ((segment[1] & 0x0F) << 8) | segment[2];
    encoded = mobilinkd::Golay24::encode24(tmp);
    for (size_t i = 24; i != 48; ++i)
    {
        result[i] = (encoded & (1 << 23)) != 0;
        encoded <<= 1;
    }

    tmp = segment[3] << 4 | ((segment[4] >> 4) & 0x0F);
    encoded = mobilinkd::Golay24::encode24(tmp);
    for (size_t i = 48; i != 72; ++i)
    {
        result[i] = (encoded & (1 << 23)) != 0;
        encoded <<= 1;
    }

    tmp = ((segment[4] & 0x0F) << 8) | (segment_number << 5);
    encoded = mobilinkd::Golay24::encode24(tmp);
    for (size_t i = 72; i != 96; ++i)
    {
        result[i] = (encoded & (1 << 23)) != 0;
        encoded <<= 1;
    }

    return result;
}

void send_audio_frame(const lich_segment_t& lich, const data_frame_t& data)
{
    using namespace mobilinkd;

    std::array<int8_t, 368> temp;
    auto it = std::copy(lich.begin(), lich.end(), temp.begin());
    std::copy(data.begin(), data.end(), it);

    M17Randomizer<368> randomizer;
    PolynomialInterleaver<45, 92, 368> interleaver;

    interleaver.interleave(temp);
    randomizer.randomize(temp);
    output_frame(SYNC_WORD, temp);
}

void transmit(queue_t& queue, const lsf_t& lsf)
{
    using namespace mobilinkd;

    lich_t lich;
    for (size_t i = 0; i != lich.size(); ++i)
    {
        std::array<uint8_t, 5> segment;
        std::copy(lsf.begin() + i * 5, lsf.begin() + (i + 1) * 5, segment.begin());
        auto lich_segment = make_lich_segment(segment, i);
        std::copy(lich_segment.begin(), lich_segment.end(), lich[i].begin());
    }
    
    struct CODEC2* codec2 = ::codec2_create(CODEC2_MODE_3200);

    M17Randomizer<368> randomizer;
    PolynomialInterleaver<45, 92, 368> interleaver;
    CRC16<0x5935, 0xFFFF> crc;

    audio_frame_t audio;
    size_t index = 0;
    uint16_t frame_number = 0;
    uint8_t lich_segment = 0;
    while (queue.is_open())
    {
        int16_t sample;
        if (!queue.get(sample, std::chrono::milliseconds(40))) break;
        audio[index++] = sample;
        if (index == audio.size())
        {
            index = 0;
            auto data = make_data_frame(frame_number++, encode(codec2, audio));
            if (frame_number == 0x8000) frame_number = 0;
            send_audio_frame(lich[lich_segment++], data);
            if (lich_segment == lich.size()) lich_segment = 0;
            audio.fill(0);
        } 
    }

    if (index > 0)
    {
        // send parial frame;
        auto data = make_data_frame(frame_number++, encode(codec2, audio));
        if (frame_number == 0x8000) frame_number = 0;
        send_audio_frame(lich[lich_segment++], data);
        if (lich_segment == lich.size()) lich_segment = 0;
    }

    // Last frame
    audio.fill(0);
    auto data = make_data_frame(frame_number | 0x8000, encode(codec2, audio));
    send_audio_frame(lich[lich_segment], data);
}

int main(int argc, char* argv[])
{
    using namespace mobilinkd;

    auto config = Config::parse(argc, argv);
    if (!config) return 0;

    bitstream = config->bitstream;

    signal(SIGINT, &signal_handler);

    send_preamble();
    auto lsf = send_lsf(config->source_address, config->destination_address);

    queue_t queue;
    std::thread thd([&queue, &lsf](){transmit(queue, lsf);});

    std::cerr << "m17-mod running. ctrl-D to break." << std::endl;

    // Input must be 8000 SPS, 16-bit LE, 1 channel raw audio.
    while (running)
    {
        int16_t sample;
        if (!std::cin.read(reinterpret_cast<char*>(&sample), 2)) break;
        if (!queue.put(sample, std::chrono::seconds(1))) break;
    }

    running = false;

    queue.close();
    thd.join();

    return EXIT_SUCCESS;
}