FMControl.cpp

/*
 *   Copyright (C) 2020,2021 by Jonathan Naylor G4KLX
 *
 *   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 2 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, write to the Free Software
 *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include "FMControl.h"

#include <string>

#if defined(DUMP_RF_AUDIO)
#include <cstdio>
#endif

#define SWAP_BYTES_16(a) (((a >> 8) & 0x00FFU) | ((a << 8) & 0xFF00U))

const float        DEEMPHASIS_GAIN_DB  = 8.0F;  // Audio gain  adjustment
const float        PREEMPHASIS_GAIN_DB = 0.0F;  // Audio gain  adjustment
const float        FILTER_GAIN_DB      = 2.0F;  // Audio gain  adjustment
const unsigned int FM_MASK             = 0x00000FFFU;

CFMControl::CFMControl(CFMNetwork* network, float txAudioGain, float rxAudioGain, bool preEmphasisOn, bool deEmphasisOn) :
m_network(network),
m_txAudioGain(txAudioGain),
m_rxAudioGain(rxAudioGain),
m_preEmphasisOn(preEmphasisOn),
m_deEmphasisOn(deEmphasisOn),
m_enabled(false),
m_incomingRFAudio(1600U, "Incoming RF FM Audio"),
m_preEmphasis(NULL),
m_deEmphasis(NULL),
m_filterStage1(NULL),
m_filterStage2(NULL),
m_filterStage3(NULL)
{
    assert(txAudioGain > 0.0F);
    assert(rxAudioGain > 0.0F);

    m_preEmphasis  = new CIIRDirectForm1Filter(8.315375384336983F, -7.03334621603483F,0.0F,1.0F, 0.282029168302153F,0.0F, PREEMPHASIS_GAIN_DB);
    m_deEmphasis   = new CIIRDirectForm1Filter(0.07708787090460224F, 0.07708787090460224F,0.0F, 1.0F, -0.8458242581907955F,0.0F, DEEMPHASIS_GAIN_DB);

    // Chebyshev type 1 0.2dB cheby type 1 3rd order 300-2700Hz fs=8000
    m_filterStage1 = new CIIRDirectForm1Filter(0.29495028f, 0.0f, -0.29495028f, 1.0f, -0.61384624f, -0.057158668f, FILTER_GAIN_DB);
    m_filterStage2 = new CIIRDirectForm1Filter(1.0f, 2.0f, 1.0f, 1.0f, 0.9946123f, 0.6050482f, FILTER_GAIN_DB);
    m_filterStage3 = new CIIRDirectForm1Filter(1.0f, -2.0f, 1.0f, 1.0f, -1.8414584f, 0.8804949f, FILTER_GAIN_DB);
}

CFMControl::~CFMControl()
{
    delete m_preEmphasis;
    delete m_deEmphasis;

    delete m_filterStage1;
    delete m_filterStage2;
    delete m_filterStage3;
}

bool CFMControl::writeModem(const unsigned char* data, unsigned int length)
{
    assert(data != NULL);
    assert(length > 0U);

    if (m_network == NULL)
        return true;

    if (data[0U] == TAG_HEADER)
        return true;

    if (data[0U] == TAG_EOT)
        return m_network->writeEnd();

    if (data[0U] != TAG_DATA)
        return false;

    m_incomingRFAudio.addData(data + 1U, length - 1U);
    unsigned int bufferLength = m_incomingRFAudio.dataSize();
    if (bufferLength > 240U)    // 160 samples 12-bit
        bufferLength = 240U;    // 160 samples 12-bit

    if (bufferLength >= 3U) {
        bufferLength = bufferLength - bufferLength % 3U;    // Round down to nearest multiple of 3
        unsigned char bufferData[240U];                     // 160 samples 12-bit       
        m_incomingRFAudio.getData(bufferData, bufferLength);

        unsigned int pack = 0U;
        unsigned char* packPointer = (unsigned char*)&pack;
        float out[160U];                                    // 160 samples 12-bit
        unsigned int nOut = 0U;
        short unpackedSamples[2U];

        for (unsigned int i = 0U; i < bufferLength; i += 3U) {
            // Extract unsigned 12 bit unsigned sample pairs packed into 3 bytes to 16 bit signed
            packPointer[0U] = bufferData[i + 0U];
            packPointer[1U] = bufferData[i + 1U];
            packPointer[2U] = bufferData[i + 2U];

            unpackedSamples[1U] = short(int(pack & FM_MASK) - 2048);
            unpackedSamples[0U] = short(int(pack >> 12 & FM_MASK) - 2048); // 

            // Process unpacked sample pair
            for (unsigned char j = 0U; j < 2U; j++) {
                // Convert to float (-1.0 to +1.0)
                float sampleFloat = (float(unpackedSamples[j]) * m_rxAudioGain) / 2048.0F;

                // De-emphasise and remove CTCSS
                if (m_deEmphasisOn)
                    sampleFloat = m_deEmphasis->filter(sampleFloat);

                out[nOut++] = m_filterStage3->filter(m_filterStage2->filter(m_filterStage1->filter(sampleFloat)));
            }
        }

#if defined(DUMP_RF_AUDIO)
        FILE * audiofile = fopen("./audiodump.bin", "ab");
        if (audiofile != NULL) {
            fwrite(out, sizeof(float), nOut, audiofile);
            fclose(audiofile);
        }
#endif
        return m_network->writeData(out, nOut);
    }

    return true;
}

unsigned int CFMControl::readModem(unsigned char* data, unsigned int space)
{
    assert(data != NULL);
    assert(space > 0U);

    if (m_network == NULL)
        return 0U;

    if (space > 240U)           // 160 samples 12-bit
        space = 240U;           // 160 samples 12-bit

    float netData[160U]; // Modem can handle up to 160 samples at a time
    unsigned int length = m_network->readData(netData, 160U);  // 160 samples 12-bit
    if (length == 0U)
        return 0U;

    unsigned int pack = 0U;
    unsigned char* packPointer = (unsigned char*)&pack;
    unsigned int nData = 0U;

    for (unsigned int i = 0; i < length; i++) {
        float sampleFloat = netData[i] * m_txAudioGain;

        // Pre-emphasis
        if (m_preEmphasisOn)
            sampleFloat = m_preEmphasis->filter(sampleFloat);

        // Convert float to 12-bit samples (0 to 4095)
        unsigned int sample12bit = (unsigned int)((sampleFloat + 1.0F) * 2048.0F + 0.5F);

        // Pack 2 samples into 3 bytes
        if ((i & 1U) == 0) {
            pack = 0U;
            pack = sample12bit << 12;
        } else {
            pack |= sample12bit;

            data[nData++] = packPointer[0U];
            data[nData++] = packPointer[1U];
            data[nData++] = packPointer[2U];
        }
    }

    return nData;
}

void CFMControl::clock(unsigned int ms)
{
    // May not be needed
}

void CFMControl::enable(bool enabled)
{
    // May not be needed
}