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m17-cxx-demod/include/m17cxx/M17Modulator.h

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22 KiB
C++
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#pragma once
#include "queue.h"
#include "FirFilter.h"
#include "LinkSetupFrame.h"
#include "CRC16.h"
#include "Convolution.h"
#include "PolynomialInterleaver.h"
#include "M17Randomizer.h"
#include "Util.h"
#include "Golay24.h"
#include "Trellis.h"
#include <codec2/codec2.h>
#include <array>
#include <atomic>
#include <chrono>
#include <cstdint>
#include <future>
#include <iostream>
#include <memory>
namespace mobilinkd
{
/**
* Asynchronous M17 modulator. This modulator is initialized with the source and
* destination callsigns. It is then run by attaching an input queue and an output
* queue. The modulator reads 16-bit, 8ksps, 1-channel audio samples from the input
* queue and an M17 bitstream (in 8-bit bytes, 4 symbols per byte) to the output queue.
*
* The call to run(), which is used to attach the queues, returns immediately, starting
* a new thread in a detached state. run() returns a future, which may contain error
* information if an exception is thrown.
*
* The modulator stops when the input queue is closed.
*
* The modulator starts in a paused state, discarding all input.
*
* The modulator is started by calling ptt_on(). This causes the preamble and link
* setup frame to be sent. The modulator then starts reading from the input queue
* and writing the data stream to the output queue.
*
* The modulator can be paused by calling ptt_off(). This will cause any audio
* samples remaining in the input queue to be discarded. The final frame will
* be sent with the EOS bit set. The output queue should always be completely
* drained and all symbols output should be transmitted to ensure proper EOS
* signalling.
*
* Output will be bursty -- their is no throttling of the symbol stream. As soon
* as enough input samples are received to fill the M17 payload field, the frame
* will be constructed and the symbol stream output on the queue.
*
* @invariant The state of the modulator is one of INACTIVE, IDLE, PREAMBLE,
* LINK_SETUP, ACTIVE, or END_OF_STREAM.
*
* The modulator transitions from INACTIVE to IDLE when run() is called.
*
* The modulator transitions from IDLE to PREAMBLE when ptt_on() is called.
*
* The modulator will transition from PREAMBLE to LINK_SETUP to ACTIVE automatically.
*
* The modulator transitions from ACTIVE to END_OF_STREAM when ptt_off() is called.
*
* The modulator transitions from END_OF_STREAM to IDLE after the last audio
* frame is emitted.
*
* The modulator will transition from IDLE to INACTIVE when the input or output
* queue is closed.
*
* The modulator will emit at least 3 frames when ptt_on() is called: the preamble,
* the link setup frame, and one audio frame with the EOS flag set.
*
* It is an error to close the input or output stream when the modulator is not IDLE.
*
* @section Thread Safety
*
* Internally, the modulator is thread-safe. It is running with a background thread
* reading from and writing to thread-safe queues. Externally, the modulator expects
* that all API calls made synchronously as if from a single thread of control.
*
* @section Convertion Functions
*
* There are two public static conversion functions provided to support conversion of
* the output bitstream into either a symbol stream or into a 48ksps baseband stream.
*/
struct M17Modulator
{
public:
using bitstream_queue_t = queue<uint8_t, 96>; // 1 frame's worth of data, 48 bytes, 192 symbols, 384 bits.
using audio_queue_t = queue<int16_t, 320>; // 1 frame's worth of data.
using symbols_t = std::array<int8_t, 192>; // One frame of symbols.
using baseband_t = std::array<int16_t, 1920>; // One frame of baseband data @ 48ksps
using bitstream_t = std::array<uint8_t, 48>; // M17 frame of bits (in bytes).
enum class State {INACTIVE, IDLE, PREAMBLE, LINK_SETUP, ACTIVE, END_OF_STREAM};
private:
using lsf_t = std::array<uint8_t, 30>; // Link setup frame bytes.
using lich_segment_t = std::array<uint8_t, 12>; // Golay-encoded LICH.
using lich_t = std::array<lich_segment_t, 6>; // All LICH segments.
using audio_frame_t = std::array<int16_t, 320>;
using codec_frame_t = std::array<uint8_t, 16>;
using payload_t = std::array<uint8_t, 34>; // Bytes in the payload of a data frame.
using frame_t = std::array<uint8_t, 46>; // M17 frame (without sync word).
static constexpr std::array<uint8_t, 2> SYNC_WORD = {0x32, 0x43};
static constexpr std::array<uint8_t, 2> LSF_SYNC_WORD = {0x55, 0xF7};
static constexpr std::array<uint8_t, 2> DATA_SYNC_WORD = {0xFF, 0x5D};
std::shared_ptr<audio_queue_t> audio_queue_; // Input queue.
std::shared_ptr<bitstream_queue_t> bitstream_queue_; // Output queue.
std::atomic<State> state_ = State::INACTIVE;
struct CODEC2* codec2_ = nullptr;
M17ByteRandomizer<46> randomizer_;
PolynomialInterleaver<45, 92, 368> interleaver_;
CRC16<0x5935, 0xFFFF> crc_;
LinkSetupFrame::encoded_call_t source_;
LinkSetupFrame::encoded_call_t dest_;
static LinkSetupFrame::encoded_call_t encode_callsign(std::string callsign)
{
LinkSetupFrame::encoded_call_t encoded_call = {0xff,0xff,0xff,0xff,0xff,0xff};
if (callsign.empty() || callsign.size() > 9) return encoded_call;
mobilinkd::LinkSetupFrame::call_t call;
call.fill(0);
std::copy(callsign.begin(), callsign.end(), call.begin());
encoded_call = LinkSetupFrame::encode_callsign(call);
return encoded_call;
}
static constexpr 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;
}
return 0;
}
template <typename T, size_t N>
static 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;
}
void output_frame(std::array<uint8_t, 2> sync_word, const frame_t& frame)
{
for (auto c : sync_word) bitstream_queue_->put(c);
for (auto c : frame) bitstream_queue_->put(c);
}
void send_preamble()
{
// Preamble is simple... bytes -> symbols.
std::array<uint8_t, 48> preamble_bytes;
preamble_bytes.fill(0x77);
for (auto c : preamble_bytes) bitstream_queue_->put(c);
}
template <typename T, size_t N>
static std::array<T, N * 2 + 1> conv_encode(std::array<T, N> data)
{
std::array<T, N * 2 + 1> result;
uint8_t bit_index = 0;
uint8_t byte_index = 0;
uint8_t tmp = 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 = update_memory<4>(memory, x);
tmp = (tmp << 1) | convolve_bit(031, memory);
tmp = (tmp << 1) | convolve_bit(027, memory);
bit_index += 2;
if (bit_index == 8)
{
bit_index = 0;
result[byte_index++] = tmp;
tmp = 0;
}
}
}
// Flush the encoder.
for (size_t i = 0; i != 4; ++i)
{
memory = update_memory<4>(memory, 0);
tmp = (tmp << 1) | convolve_bit(031, memory);
tmp = (tmp << 1) | convolve_bit(027, memory);
bit_index += 2;
if (bit_index == 8)
{
bit_index = 0;
result[byte_index++] = tmp;
tmp = 0;
}
}
// Frame may not end on a byte boundary.
if (bit_index != 0)
{
while (bit_index++ != 8) tmp <<= 1;
result[byte_index] = tmp;
}
return result;
}
/**
* 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)
{
assign_bit_index(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)
{
assign_bit_index(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)
{
assign_bit_index(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)
{
assign_bit_index(result, i, (encoded & (1 << 23)) != 0);
encoded <<= 1;
}
return result;
}
/**
* Construct the link setup frame and split into LICH segments. Output the
* link setup frame and return the LICH segments to the caller.
*/
void send_link_setup(lich_t& lich)
{
using namespace mobilinkd;
lsf_t lsf;
lsf.fill(0);
auto rit = std::copy(source_.begin(), source_.end(), lsf.begin());
std::copy(dest_.begin(), dest_.end(), rit);
lsf[12] = 0;
lsf[13] = 5;
crc_.reset();
for (size_t i = 0; i != 28; ++i)
{
crc_(lsf[i]);
}
auto checksum = crc_.get_bytes();
lsf[28] = checksum[0];
lsf[29] = checksum[1];
// Build LICH segments
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());
}
auto encoded = conv_encode(lsf);
std::array<uint8_t, 46> punctured;
auto size = puncture_bytes(encoded, punctured, P1);
assert(size == 368);
interleaver_.interleave(punctured);
randomizer_(punctured);
output_frame(LSF_SYNC_WORD, punctured);
}
/**
* Append the LICH and Convolutionally encoded payload, interleave and randomize
* the frame bits, and output the frame.
*/
void send_audio_frame(const lich_segment_t& lich, const payload_t& data)
{
using namespace mobilinkd;
std::array<uint8_t, 46> temp;
auto it = std::copy(lich.begin(), lich.end(), temp.begin());
std::copy(data.begin(), data.end(), it);
interleaver_.interleave(temp);
randomizer_(temp);
output_frame(DATA_SYNC_WORD, temp);
}
/**
* Assemble the audio frame payload by appending the frame number, encoded audio,
* and CRC, then convolutionally coding and puncturing the data.
*/
payload_t make_payload(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);
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];
auto encoded = conv_encode(data);
payload_t punctured;
auto size = puncture_bytes(encoded, punctured, mobilinkd::P2);
assert(size == 272);
return punctured;
}
/**
* 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_audio(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;
}
/**
* Send the audio frame. Encodes the audio, assembles the audio frame, and
* outputs the frame on the queue.
*/
void send_audio(const lich_segment_t& lich, uint16_t frame_number, const audio_frame_t& audio)
{
auto encoded_audio = encode_audio(audio);
auto payload = make_payload(frame_number, encoded_audio);
send_audio_frame(lich, payload);
}
/**
* Modulator state machine. Controls state transitions, ensuring that the
* M17 stream is sent and terminated appropriately.
*/
void modulate()
{
using namespace std::chrono_literals;
using clock = std::chrono::steady_clock;
state_ = State::IDLE;
codec2_ = ::codec2_create(CODEC2_MODE_3200);
lich_t lich;
size_t index = 0;
uint16_t frame_number = 0;
uint8_t lich_segment = 0;
audio_frame_t audio;
auto current = clock::now();
audio.fill(0);
while (audio_queue_->is_open() && bitstream_queue_->is_open())
{
int16_t sample;
if (!(audio_queue_->get(sample, 5s))) sample = 0; // May be closed.
if (!(audio_queue_->is_open()))
{
std::clog << "audio output queue closed" << std::endl;
break;
}
switch (state_)
{
case State::IDLE:
break;
case State::PREAMBLE:
send_preamble();
state_ = State::LINK_SETUP;
break;
case State::LINK_SETUP:
send_link_setup(lich);
index = 0;
frame_number = 0;
lich_segment = 0;
state_ = State::ACTIVE;
current = clock::now();
break;
case State::ACTIVE:
audio[index++] = sample;
if (index == audio.size())
{
auto now = clock::now();
if (now - current > 40ms)
{
std::clog << "WARNING: packet time exceeded" << std::endl;
}
current = now;
index = 0;
send_audio(lich[lich_segment++], frame_number++, audio);
if (frame_number == 0x8000) frame_number = 0;
if (lich_segment == lich.size()) lich_segment = 0;
audio.fill(0);
}
break;
case State::END_OF_STREAM:
audio[index++] = sample;
send_audio(lich[lich_segment++], frame_number++, audio);
audio.fill(0);
state_ = State::IDLE;
break;
default:
assert(false && "Invalid state");
}
}
::codec2_destroy(codec2_);
codec2_ = nullptr;
if (state_ != State::IDLE) throw std::logic_error("queue closed when not IDLE");
state_ = State::INACTIVE;
}
public:
M17Modulator(const std::string& source, const std::string& dest = "")
: source_(encode_callsign(source))
, dest_(encode_callsign(dest))
{}
/**
* Set the source identifier (callsign) for the transmitter.
*/
void source(const std::string& callsign)
{
source_ = encode_callsign(callsign);
}
/**
* Set the destination identifier for the transmitter. A blank value is
* interpreted as the broadcast address. This is the default.
*/
void dest(const std::string& callsign)
{
dest_ = encode_callsign(callsign);
}
/**
* Start the modulator. This starts a background thread and returns once the thread
* has started and changed the state to IDLE.
*
* @pre state is INACTIVE.
*
* @param input is a shared pointer to the audio input queue.
* @param output is a shared pointer to the symbol output queue.
* @return a future which is used to return error information to the caller.
*/
std::future<void> run(const std::shared_ptr<audio_queue_t>& input, const std::shared_ptr<bitstream_queue_t>& output)
{
using namespace std::chrono_literals;
assert(state_ == State::INACTIVE);
audio_queue_ = input;
bitstream_queue_ = output;
auto result = std::async(std::launch::async, [this](){
this->modulate();
});
// Wait until thread is active.
while (state_ != State::IDLE) std::this_thread::yield();
return result;
}
/**
* Activate the modulator. This causes the modulator to transition from IDLE to
* ACTIVE. If the modulator is already ACTIVE, no action is taken. If the modulator
* is not IDLE, return is delayed until the modulator becomes IDLE (which may take
* up to 120ms), at which time the modulator is returned to the ACTIVE state.
* Otherwise the modulator immediately transistions from IDLE to ACTIVE. This will
* cause the preamble and link setup frames to be emitted.
*
* @pre run must have been called.
* @pre the input queue must be open.
* @pre the output queue must be open.
*/
void ptt_on()
{
using namespace std::chrono_literals;
assert(state_ != State::INACTIVE);
assert(audio_queue_ && audio_queue_->is_open());
assert(bitstream_queue_ && bitstream_queue_->is_open());
if (state_ == State::ACTIVE) return;
while (state_ != State::IDLE && state_ != State::INACTIVE) std::this_thread::sleep_for(1ms);
assert(state_ == State::IDLE); // Precondition violated -- one of the queues was closed.
state_ = State::PREAMBLE;
}
/**
* Stop the modulator.
*
* @pre ptt_on() was called and the modulator is in PREAMBLE, LINK_SETUP, or ACTIVE state.
*/
void ptt_off()
{
using namespace std::chrono_literals;
assert(state_ == State::PREAMBLE | state_ == State::LINK_SETUP | state_ == State::ACTIVE);
// State must become active before we release PTT to ensure preamble and LSF are sent.
while (state_ != State::ACTIVE && state_ != State::INACTIVE) std::this_thread::sleep_for(1ms);
assert(state_ == State::ACTIVE); // Precondition violated -- one of the queues was closed.
state_ = State::END_OF_STREAM;
}
void wait_until_idle()
{
using namespace std::chrono_literals;
while (state_ != State::IDLE && state_ != State::INACTIVE) std::this_thread::sleep_for(1ms);
}
void wait_until_inactive()
{
using namespace std::chrono_literals;
while (state_ != State::INACTIVE) std::this_thread::sleep_for(1ms);
}
State state() const { return state_; }
template <typename T, size_t N>
static 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;
}
static baseband_t symbols_to_baseband(const symbols_t& symbols)
{
// Generated using scikit-commpy
static const auto rrc_taps = std::array<double, 79>{
-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
};
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;
}
return baseband;
}
};
} // mobilinkd
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