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Moved code of compensating filter for MDx PWM-based DAC to a dedicated class.

This commit is contained in:
Silvano Seva 2022-08-13 09:38:36 +02:00
parent d11bb903b1
commit b5fc9b252d
5 changed files with 107 additions and 57 deletions
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11
openrtx/include/core/dsp.h
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@ -55,17 +55,6 @@ filter_state_t;
*/
void dsp_resetFilterState(filter_state_t *state);
/**
* Compensate for the filtering applied by the PWM output over the modulated
* signal. The buffer is be processed in place to save memory.
*
* @param state: pointer to the data structure containing the filter state.
* @param buffer: the buffer to be used as both source and destination.
* @param length: the length of the input buffer.
*/
void dsp_pwmCompensate(filter_state_t *state, audio_sample_t *buffer,
size_t length);
/**
* Remove the DC offset from a collection of audio samples, processing data
* in-place.

4
openrtx/include/protocols/M17/M17Modulator.hpp
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@ -27,10 +27,10 @@
#include <interfaces/audio_stream.h>
#include <M17/M17Constants.hpp>
#include <M17/PwmCompensator.hpp>
#include <cstdint>
#include <memory>
#include <array>
#include <dsp.h>
namespace M17
{
@ -115,7 +115,7 @@ private:
bool txRunning; ///< Transmission running.
#if defined(PLATFORM_MD3x0) || defined(PLATFORM_MDUV3x0)
filter_state_t pwmFilterState;
PwmCompensator pwmComp;
#endif
};

99
openrtx/include/protocols/M17/PwmCompensator.hpp Normal file
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@ -0,0 +1,99 @@
/***************************************************************************
* Copyright (C) 2022 by Federico Amedeo Izzo IU2NUO, *
* Niccolò Izzo IU2KIN, *
* Silvano Seva IU2KWO, *
* Frederik Saraci IU2NRO *
* *
* 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 PWMCOMPENSATOR_H
#define PWMCOMPENSATOR_H
#ifndef __cplusplus
#error This header is C++ only!
#endif
#include <array>
#include <cstddef>
#include <cstdint>
/**
* Compensation filter for MDx PWM-based baseband output.
*/
class PwmCompensator
{
public:
/**
* Constructor.
*/
PwmCompensator()
{
reset();
}
/**
* Destructor.
*/
~PwmCompensator() { }
/**
* Perform one step of the filter, computing a new output value given
* the input value and the history of previous input values.
*
* @param input: input value for the current time step.
* @return output as a function of the current and past input values.
*/
float operator()(const float& input)
{
u[0] = input;
y[0] = (a/d)*(u[0])
+ (b/d)*(u[1])
+ (c/d)*(u[2])
- (e/d)*(y[1])
- (f/d)*(y[2]);
for(size_t i = 2; i > 0; i--)
{
u[i] = u[i - 1];
y[i] = y[i - 1];
}
return y[0] * 0.5f;
}
/**
* Reset history, clearing the memory of past values.
*/
void reset()
{
u.fill(0.0f);
y.fill(0.0f);
}
private:
static constexpr float a = 4982680082321166792352.0f;
static constexpr float b = -6330013275146484168000.0f;
static constexpr float c = 1871109008789062500000.0f;
static constexpr float d = 548027992248535162477.0f;
static constexpr float e = -24496793746948241250.0f;
static constexpr float f = 244617462158203125.0f;
std::array< float, 3 > u; ///< History of past inputs.
std::array< float, 3 > y; ///< History of past outputs.
};
#endif /* PWMCOMPENSATOR_H */

37
openrtx/src/core/dsp.cpp
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@ -33,43 +33,6 @@ void dsp_resetFilterState(filter_state_t *state)
state->initialised = false;
}
void dsp_pwmCompensate(filter_state_t *state, audio_sample_t *buffer,
size_t length)
{
static constexpr float a = 4982680082321166792352.0f;
static constexpr float b = -6330013275146484168000.0f;
static constexpr float c = 1871109008789062500000.0f;
static constexpr float d = 548027992248535162477.0f;
static constexpr float e = -24496793746948241250.0f;
static constexpr float f = 244617462158203125.0f;
// Initialise filter with first two values, for smooth transient.
if(length <= 2) return;
if(state->initialised == false)
{
state->u[2] = static_cast< float >(buffer[0]);
state->u[1] = static_cast< float >(buffer[1]);
state->initialised = true;
}
for(size_t i = 2; i < length; i++)
{
state->u[0] = static_cast< float >(buffer[i]);
state->y[0] = (a/d)*(state->u[0])
+ (b/d)*(state->u[1])
+ (c/d)*(state->u[2])
- (e/d)*(state->y[1])
- (f/d)*(state->y[2]);
state->u[2] = state->u[1];
state->u[1] = state->u[0];
state->y[2] = state->y[1];
state->y[1] = state->y[0];
buffer[i] = static_cast< audio_sample_t >((state->y[0] * 0.5f) + 0.5f);
}
}
void dsp_dcRemoval(filter_state_t *state, audio_sample_t *buffer, size_t length)
{
/*

13
openrtx/src/protocols/M17/M17Modulator.cpp
View File

@ -54,7 +54,7 @@ void M17Modulator::init()
idleBuffer = baseband_buffer.get();
txRunning = false;
#if defined(PLATFORM_MD3x0) || defined(PLATFORM_MDUV3x0)
dsp_resetFilterState(&pwmFilterState);
pwmComp.reset();
#endif
}
@ -147,7 +147,7 @@ void M17Modulator::stop()
idleBuffer = baseband_buffer.get();
#if defined(PLATFORM_MD3x0) || defined(PLATFORM_MDUV3x0)
dsp_resetFilterState(&pwmFilterState);
pwmComp.reset();
#endif
}
@ -164,13 +164,12 @@ void M17Modulator::symbolsToBaseband()
{
float elem = static_cast< float >(idleBuffer[i]);
elem = M17::rrc_48k(elem * M17_RRC_GAIN) - M17_RRC_OFFSET;
#if defined(PLATFORM_MD3x0) || defined(PLATFORM_MDUV3x0)
elem = pwmComp(elem);
elem *= -1.0f; // Invert signal phase
#endif
idleBuffer[i] = static_cast< int16_t >(elem);
}
#if defined(PLATFORM_MD3x0) || defined(PLATFORM_MDUV3x0)
dsp_pwmCompensate(&pwmFilterState, idleBuffer, M17_FRAME_SAMPLES);
dsp_invertPhase(idleBuffer, M17_FRAME_SAMPLES);
#endif
}
#ifndef PLATFORM_LINUX