Reorganized code for M17 transmission: removed M17Transmitter class, use M17FrameEncoder to assemble LSF and data frames, modified API of M17Modulator class.

meson.build

@@ -57,7 +57,6 @@ openrtx_src = ['openrtx/src/core/state.c',
                'openrtx/src/protocols/M17/M17Demodulator.cpp',
                'openrtx/src/protocols/M17/M17FrameEncoder.cpp',
                'openrtx/src/protocols/M17/M17FrameDecoder.cpp',
-               'openrtx/src/protocols/M17/M17Transmitter.cpp',
                'openrtx/src/protocols/M17/M17LinkSetupFrame.cpp']
 
 openrtx_inc = ['openrtx/include',

openrtx/include/protocols/M17/M17Modulator.hpp

@@ -62,31 +62,32 @@ public:
      */
     void terminate();
 
+    /**
+     * Start baseband transmission and send an 80ms preamble.
+     */
+    void start();
+
     /**
      * Generate and transmit the baseband signal obtained by 4FSK modulation of
-     * a given block of data. When called for the first time, this function
+     * a given block of data.
-     * starts baseband transmission.
      *
-     * @param sync: synchronisation word to be prepended to data block.
+     * @param frame: M17 frame to be sent.
-     * @param data: data block to be transmitted.
      * @param isLast: flag signalling that current block is the last one being
      * transmitted.
      */
-    void send(const std::array< uint8_t, 2 >& sync,
+    void send(const frame_t& frame, const bool isLast);
-              const std::array< uint8_t, 46 >& data,
-              const bool isLast = false);
 
 private:
 
     /**
      * Generate baseband stream from symbol stream.
      */
-    void generateBaseband();
+    void symbolsToBaseband();
 
     /**
      * Emit the baseband stream towards the output stage, platform dependent.
      */
-    void emitBaseband();
+    void sendBaseband();
 
     static constexpr size_t M17_TX_SAMPLE_RATE     = 48000;
     static constexpr size_t M17_SAMPLES_PER_SYMBOL = M17_TX_SAMPLE_RATE / M17_SYMBOL_RATE;
@@ -100,7 +101,7 @@ private:
     static constexpr float  M17_RRC_OFFSET        = 0.0f;
     #endif
 
-    std::array< int16_t, M17_FRAME_SYMBOLS > symbols;
+    std::array< int8_t, M17_FRAME_SYMBOLS > symbols;
     std::unique_ptr< int16_t[] > baseband_buffer;  ///< Buffer for baseband audio handling.
     stream_sample_t              *idleBuffer;      ///< Half baseband buffer, free for processing.
     streamId                     outStream;        ///< Baseband output stream ID.

openrtx/include/protocols/M17/M17Transmitter.hpp

@@ -1,95 +0,0 @@
-/***************************************************************************
- *   Copyright (C) 2021 - 2022 by Federico Amedeo Izzo IU2NUO,             *
- *                                Niccolò Izzo IU2KIN                      *
- *                                Frederik Saraci IU2NRO                   *
- *                                Silvano Seva IU2KWO                      *
- *                                                                         *
- *   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 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 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/>   *
- ***************************************************************************/
-
-#ifndef M17TRANSMITTER_H
-#define M17TRANSMITTER_H
-
-#ifndef __cplusplus
-#error This header is C++ only!
-#endif
-
-#include <string>
-#include <array>
-#include "M17ConvolutionalEncoder.hpp"
-#include "M17LinkSetupFrame.hpp"
-#include "M17StreamFrame.hpp"
-#include "M17Modulator.hpp"
-
-namespace M17
-{
-
-/**
- * M17 transmitter.
- */
-class M17Transmitter
-{
-public:
-
-    /**
-     * Constructor.
-     *
-     * @param modulator: reference to M17 4FSK modulator driver.
-     */
-    M17Transmitter(M17Modulator& modulator);
-
-    /**
-     * Destructor.
-     */
-    ~M17Transmitter();
-
-    /**
-     * Start a new data stream with broadcast destination callsign.
-     *
-     * @param src: source callsign.
-     */
-    void start(const std::string& src);
-
-    /**
-     * Start a new data stream with given destination callsign. If destination
-     * callsing is empty, the stream falls back to broadcast transmission.
-     *
-     * @param src: source callsign.
-     * @param dst: destination callsign.
-     */
-    void start(const std::string& src, const std::string& dst);
-
-    /**
-     * Send a block of data.
-     *
-     * @param payload: payload data.
-     * @param isLast: if true, current frame is marked as the last one to be
-     * transmitted.
-     */
-    void send(const payload_t& payload, const bool isLast = false);
-
-private:
-
-    M17ConvolutionalEncoder      encoder;    ///< Convolutional encoder.
-    M17LinkSetupFrame                lsf;    ///< Link Setup Frame handler.
-    M17StreamFrame             dataFrame;    ///< Data frame Handler.
-    M17Modulator&              modulator;    ///< 4FSK modulator.
-    std::array< lich_t, 6 > lichSegments;    ///< Encoded LSF chunks for LICH generation.
-    uint8_t                  currentLich;    ///< Index of current LSF chunk.
-    uint16_t                 frameNumber;    ///< Current frame number.
-};
-
-} /* M17 */
-
-#endif /* M17TRANSMITTER_H */

openrtx/include/rtx/OpMode_M17.hpp

@@ -22,7 +22,7 @@
 #define OPMODE_M17_H
 
 #include <M17/M17FrameDecoder.hpp>
-#include <M17/M17Transmitter.hpp>
+#include <M17/M17FrameEncoder.hpp>
 #include <M17/M17Demodulator.hpp>
 #include <M17/M17Modulator.hpp>
 #include "OpMode.hpp"
@@ -126,8 +126,8 @@ private:
     bool locked;                       ///< Demodulator locked on data stream.
     M17::M17Modulator    modulator;    ///< M17 modulator.
     M17::M17Demodulator  demodulator;  ///< M17 demodulator.
-    M17::M17Transmitter  m17Tx;        ///< M17 transmission manager.
     M17::M17FrameDecoder decoder;      ///< M17 frame decoder
+    M17::M17FrameEncoder encoder;      ///< M17 frame encoder
 };
 
 #endif /* OPMODE_M17_H */

openrtx/src/protocols/M17/M17Modulator.cpp

@@ -47,8 +47,7 @@ void M17Modulator::init()
 {
     /*
      * Allocate a chunk of memory to contain two complete buffers for baseband
-     * audio. Split this chunk in two separate blocks for double buffering using
+     * audio.
-     * placement new.
      */
 
     baseband_buffer = std::make_unique< int16_t[] >(2 * M17_FRAME_SAMPLES);
@@ -72,30 +71,55 @@ void M17Modulator::terminate()
     baseband_buffer.reset();
 }
 
-void M17Modulator::send(const std::array< uint8_t, 2 >& sync,
+void M17::M17Modulator::start()
-                        const std::array< uint8_t, 46 >& data,
-                        const bool isLast)
 {
-    auto sync1 = byteToSymbols(sync[0]);
+    if(txRunning) return;
-    auto sync2 = byteToSymbols(sync[1]);
 
-    auto it = std::copy(sync1.begin(), sync1.end(), symbols.begin());
+    txRunning = true;
-         it = std::copy(sync2.begin(), sync2.end(), it);
+    stopTx    = false;
 
-    for(size_t i = 0; i < data.size(); i++)
+    // Fill symbol buffer with preamble, made of alternated +3 and -3 symbols
+    for(size_t i = 0; i < symbols.size(); i += 2)
     {
-        auto sym = byteToSymbols(data[i]);
+        symbols[i]     = +3;
+        symbols[i + 1] = -3;
+    }
+
+    // Generate baseband signal and then start transmission
+    symbolsToBaseband();
+    #ifndef PLATFORM_LINUX
+    outStream = outputStream_start(SINK_RTX, PRIO_TX, baseband_buffer.get(),
+                                   2*M17_FRAME_SAMPLES, BUF_CIRC_DOUBLE,
+                                   M17_TX_SAMPLE_RATE);
+    idleBuffer = outputStream_getIdleBuffer(outStream);
+    #else
+    sendBaseband();
+    #endif
+
+    // Repeat baseband generation and transmission, this makes the preamble to
+    // be long 80ms (two frames)
+    symbolsToBaseband();
+    sendBaseband();
+}
+
+
+void M17Modulator::send(const frame_t& frame, const bool isLast)
+{
+    auto it = symbols.begin();
+    for(size_t i = 0; i < frame.size(); i++)
+    {
+        auto sym = byteToSymbols(frame[i]);
         it       = std::copy(sym.begin(), sym.end(), it);
     }
 
     // If last frame, signal stop of transmission
     if(isLast) stopTx = true;
 
-    generateBaseband();
+    symbolsToBaseband();
-    emitBaseband();
+    sendBaseband();
 }
 
-void M17Modulator::generateBaseband()
+void M17Modulator::symbolsToBaseband()
 {
     memset(idleBuffer, 0x00, M17_FRAME_SAMPLES * sizeof(stream_sample_t));
 
@@ -110,33 +134,20 @@ void M17Modulator::generateBaseband()
         elem          = M17::rrc_48k(elem * M17_RRC_GAIN) - M17_RRC_OFFSET;
         idleBuffer[i] = static_cast< int16_t >(elem);
     }
-}
 
-#ifndef PLATFORM_LINUX
-void M17Modulator::emitBaseband()
-{
     #if defined(PLATFORM_MD3x0) || defined(PLATFORM_MDUV3x0)
     dsp_pwmCompensate(&pwmFilterState, idleBuffer, M17_FRAME_SAMPLES);
     dsp_invertPhase(idleBuffer, M17_FRAME_SAMPLES);
     #endif
+}
 
-    if(txRunning == false)
+#ifndef PLATFORM_LINUX
-    {
+void M17Modulator::sendBaseband()
-        // First run, start transmission
+{
-        outStream = outputStream_start(SINK_RTX,
+    if(txRunning == false) return;
-                                       PRIO_TX,
+
-                                       baseband_buffer.get(),
+    // Transmission is ongoing, syncronise with stream end before proceeding
-                                       2*M17_FRAME_SAMPLES,
+    outputStream_sync(outStream, true);
-                                       BUF_CIRC_DOUBLE,
-                                       M17_TX_SAMPLE_RATE);
-        txRunning = true;
-        stopTx    = false;
-    }
-    else
-    {
-        // Transmission is ongoing, syncronise with stream end before proceeding
-        outputStream_sync(outStream, true);
-    }
 
     // Check if transmission stop is requested, if so stop the output stream
     // and wait until its effective termination.
@@ -157,7 +168,7 @@ void M17Modulator::emitBaseband()
     }
 }
 #else
-void M17Modulator::emitBaseband()
+void M17Modulator::sendBaseband()
 {
     FILE *outfile = fopen("/tmp/m17_output.raw", "ab");
 

openrtx/src/protocols/M17/M17Transmitter.cpp

@@ -1,124 +0,0 @@
-/***************************************************************************
- *   Copyright (C) 2021 by Federico Amedeo Izzo IU2NUO,                    *
- *                         Niccolò Izzo IU2KIN                             *
- *                         Frederik Saraci IU2NRO                          *
- *                         Silvano Seva IU2KWO                             *
- *                                                                         *
- *   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 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 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 <M17/M17CodePuncturing.hpp>
-#include <M17/M17Decorrelator.hpp>
-#include <M17/M17Interleaver.hpp>
-#include <M17/M17Transmitter.hpp>
-
-using namespace M17;
-
-M17Transmitter::M17Transmitter(M17Modulator& modulator) : modulator(modulator),
-                                                currentLich(0), frameNumber(0)
-{
-
-}
-
-M17Transmitter::~M17Transmitter()
-{
-
-}
-
-void M17Transmitter::start(const std::string& src)
-{
-    // Just call start() with an empty string for destination callsign.
-    std::string empty;
-    start(src, empty);
-}
-
-void M17Transmitter::start(const std::string& src, const std::string& dst)
-{
-    // Reset LICH and frame counters
-    currentLich = 0;
-    frameNumber = 0;
-
-    // Fill the Link Setup Frame
-    lsf.clear();
-    lsf.setSource(src);
-    if(!dst.empty()) lsf.setDestination(dst);
-
-    streamType_t type;
-    type.fields.stream   = 1;    // Stream
-    type.fields.dataType = 2;    // Voice data
-    type.fields.CAN      = 0;  // Channel access number
-
-    lsf.setType(type);
-    lsf.updateCrc();
-
-    // Generate the Golay(24,12) LICH segments
-    for(size_t i = 0; i < lichSegments.size(); i++)
-    {
-        lichSegments[i] = lsf.generateLichSegment(i);
-    }
-
-    // Encode the LSF, then puncture and decorrelate its data
-    std::array<uint8_t, 61> encoded;
-    encoder.reset();
-    encoder.encode(lsf.getData(), encoded.data(), sizeof(M17LinkSetupFrame));
-    encoded[60] = encoder.flush();
-
-    std::array<uint8_t, 46> punctured;
-    puncture(encoded, punctured, LSF_PUNCTURE);
-    interleave(punctured);
-    decorrelate(punctured);
-
-    // Send preamble
-    std::array<uint8_t, 2>  preamble_sync;
-    std::array<uint8_t, 46> preamble_bytes;
-    preamble_sync.fill(0x77);
-    preamble_bytes.fill(0x77);
-    modulator.send(preamble_sync, preamble_bytes);
-
-    // Send LSF
-    modulator.send(LSF_SYNC_WORD, punctured);
-}
-
-void M17Transmitter::send(const payload_t& payload, const bool isLast)
-{
-    dataFrame.clear();
-    dataFrame.setFrameNumber(frameNumber);
-    frameNumber = (frameNumber + 1) & 0x07FF;
-    if(isLast) dataFrame.lastFrame();
-    std::copy(payload.begin(), payload.end(), dataFrame.payload().begin());
-
-    // Encode frame
-    std::array<uint8_t, 37> encoded;
-    encoder.reset();
-    encoder.encode(dataFrame.getData(), encoded.data(), sizeof(M17StreamFrame));
-    encoded[36] = encoder.flush();
-
-    std::array<uint8_t, 34> punctured;
-    puncture(encoded, punctured, DATA_PUNCTURE);
-
-    // Add LICH segment to coded data and send
-    std::array<uint8_t, 46> frame;
-    auto it = std::copy(lichSegments[currentLich].begin(),
-                        lichSegments[currentLich].end(),
-                        frame.begin());
-    std::copy(punctured.begin(), punctured.end(), it);
-
-    // Increment LICH counter after copy
-    currentLich = (currentLich + 1) % lichSegments.size();
-
-    interleave(frame);
-    decorrelate(frame);
-
-    modulator.send(STREAM_SYNC_WORD, frame, isLast);
-}

openrtx/src/rtx/OpMode_M17.cpp

@@ -29,8 +29,7 @@
 using namespace std;
 using namespace M17;
 
-OpMode_M17::OpMode_M17() : startRx(false), startTx(false), locked(false),
+OpMode_M17::OpMode_M17() : startRx(false), startTx(false), locked(false)
-                           m17Tx(modulator)
 {
 
 }
@@ -190,18 +189,37 @@ void OpMode_M17::rxState(rtxStatus_t *const status)
 
 void OpMode_M17::txState(rtxStatus_t *const status)
 {
+    frame_t m17Frame;
+
     if(startTx)
     {
+        startTx = false;
+
+        std::string src(status->source_address);
+        std::string dst(status->destination_address);
+        M17LinkSetupFrame lsf;
+
+        lsf.clear();
+        lsf.setSource(src);
+        if(!dst.empty()) lsf.setDestination(dst);
+
+        streamType_t type;
+        type.fields.stream   = 1;   // Stream
+        type.fields.dataType = 2;   // Voice data
+        type.fields.CAN      = 0;   // Channel access number
+
+        lsf.setType(type);
+        lsf.updateCrc();
+
+        encoder.reset();
+        encoder.encodeLsf(lsf, m17Frame);
+
         audio_enableMic();
         codec_startEncode(SOURCE_MIC);
-
         radio_enableTx();
 
-        std::string source_address(status->source_address);
+        modulator.start();
-        std::string destination_address(status->destination_address);
+        modulator.send(m17Frame, false);
-        m17Tx.start(source_address, destination_address);
-
-        startTx = false;
     }
 
     payload_t dataFrame;
@@ -218,5 +236,6 @@ void OpMode_M17::txState(rtxStatus_t *const status)
         status->opStatus = OFF;
     }
 
-    m17Tx.send(dataFrame, lastFrame);
+    encoder.encodeStreamFrame(dataFrame, m17Frame, lastFrame);
+    modulator.send(m17Frame, lastFrame);
 }