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M17 4FSK modulator class

This commit is contained in:
Silvano Seva 2021-08-23 19:00:57 +02:00
parent f7bec2358b
commit 39e41ee470
2 changed files with 289 additions and 0 deletions
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115
openrtx/include/protocols/M17/M17Modulator.h Normal file
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/***************************************************************************
* 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/> *
***************************************************************************/
#ifndef M17_MODULATOR_H
#define M17_MODULATOR_H
#ifndef __cplusplus
#error This header is C++ only!
#endif
#include <cstdint>
#include <array>
/**
* Modulator device for M17 protocol.
*/
class M17Modulator
{
public:
/**
* Constructor.
*/
M17Modulator();
/**
* Destructor.
*/
~M17Modulator();
/**
* Allocate buffers for baseband audio generation and initialise modulator.
*/
void init();
/**
* Shutdown modulator and deallocate data buffers.
*/
void terminate();
/**
* Generate and transmit the baseband signal obtained by 4FSK modulation of
* a given block of data.
*
* @param sync: synchronisation word to be prepended to data block.
* @param data: data block to be transmitted.
*/
void send(const std::array< uint8_t, 2 >& sync,
const std::array< uint8_t, 46 >& data);
private:
/**
* Generate baseband stream from symbol stream.
*/
void generateBaseband();
/**
* Emit the baseband stream towards the output stage, platform dependent.
*/
void emitBaseband();
/**
* Utility function to encode a given byte of data into 4FSK symbols. Each
* byte is encoded in four symbols.
*
* @param value: value to be encoded in 4FSK symbols.
* @return std::array containing the four symbols obtained by 4FSK encoding.
*/
inline std::array< int8_t, 4 > byteToSymbols(uint8_t value)
{
static constexpr int8_t LUT[] = { +1, +3, -1, -3};
std::array< int8_t, 4 > symbols;
symbols[3] = LUT[value & 0x03];
value >>= 2;
symbols[2] = LUT[value & 0x03];
value >>= 2;
symbols[1] = LUT[value & 0x03];
value >>= 2;
symbols[0] = LUT[value & 0x03];
return symbols;
}
static constexpr size_t M17_RTX_SAMPLE_RATE = 48000;
static constexpr size_t M17_FRAME_SAMPLES = 1920;
static constexpr size_t M17_FRAME_SYMBOLS = 192;
using dataBuffer_t = std::array< int16_t, M17_FRAME_SAMPLES >;
std::array< int16_t, M17_FRAME_SYMBOLS > symbols;
int16_t *baseband_buffer; ///< Buffer for baseband audio handling.
dataBuffer_t *activeBuffer; ///< Half baseband buffer, in transmission.
dataBuffer_t *idleBuffer; ///< Half baseband buffer, free for processing.
};
#endif /* M17_MODULATOR_H */

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openrtx/src/protocols/M17/M17Modulator.cpp Normal file
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/***************************************************************************
* 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 <new>
#include <dsp.h>
#include <cstddef>
#include <experimental/array>
#include <M17/M17Modulator.h>
#if defined(PLATFORM_MD3x0) || defined(PLATFORM_MDUV3x0)
#include <toneGenerator_MDx.h>
#elif defined(PLATFORM_LINUX)
#include <stdio.h>
#endif
/*
* Coefficients for M17 RRC filter
*/
const auto rrc_taps = std::experimental::make_array<float>
(
-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
);
/*
* FIR implementation of the RRC filter for baseband audio generation.
*/
static Fir< std::tuple_size< decltype(rrc_taps) >::value > rrc(rrc_taps);
M17Modulator::M17Modulator()
{
}
M17Modulator::~M17Modulator()
{
terminate();
}
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
* placement new.
*/
baseband_buffer = new int16_t[2 * M17_FRAME_SAMPLES];
activeBuffer = new (baseband_buffer) dataBuffer_t;
int16_t *ptr = baseband_buffer + activeBuffer->size();
idleBuffer = new (ptr) dataBuffer_t;
}
void M17Modulator::terminate()
{
// Delete the buffers and deallocate memory.
activeBuffer->~dataBuffer_t();
idleBuffer->~dataBuffer_t();
delete[] baseband_buffer;
}
void M17Modulator::send(const std::array< uint8_t, 2 >& sync,
const std::array< uint8_t, 46 >& data)
{
auto sync1 = byteToSymbols(sync[0]);
auto sync2 = byteToSymbols(sync[1]);
auto it = std::copy(sync1.begin(), sync1.end(), symbols.begin());
it = std::copy(sync2.begin(), sync2.end(), it);
for(size_t i = 0; i < data.size(); i++)
{
auto sym = byteToSymbols(data[i]);
it = std::copy(sym.begin(), sym.end(), it);
}
generateBaseband();
emitBaseband();
}
void M17Modulator::generateBaseband()
{
idleBuffer->fill(0);
for(size_t i = 0; i < symbols.size(); i++)
{
idleBuffer->at(i * 10) = symbols[i];
}
for(size_t i = 0; i < idleBuffer->size(); i++)
{
float elem = static_cast< float >(idleBuffer->at(i));
idleBuffer->at(i) = static_cast< int16_t >(rrc(elem) * 7168.0);
}
}
#if defined(PLATFORM_MD3x0) || defined(PLATFORM_MDUV3x0)
void M17Modulator::emitBaseband()
{
dsp_pwmCompensate(idleBuffer->data(), idleBuffer->size());
dsp_invertPhase(idleBuffer->data(), idleBuffer->size());
for(size_t i = 0; i < M17_FRAME_SAMPLES; i++)
{
int32_t pos_sample = idleBuffer->at(i) + 32768;
uint16_t shifted_sample = pos_sample >> 8;
idleBuffer->at(i) = shifted_sample;
}
toneGen_waitForStreamEnd();
std::swap(idleBuffer, activeBuffer);
toneGen_playAudioStream(reinterpret_cast< uint16_t *>(activeBuffer->data()),
activeBuffer->size(), M17_RTX_SAMPLE_RATE);
}
#elif defined(PLATFORM_LINUX)
void M17Modulator::emitBaseband()
{
std::swap(idleBuffer, activeBuffer);
FILE *outfile = fopen("/tmp/m17_output.raw", "ab");
for(auto s : *activeBuffer)
{
fwrite(&s, sizeof(s), 1, outfile);
}
fclose(outfile);
}
#else
void M17Modulator::emitBaseband() { }
#endif