portapack-mayhem/firmware/baseband/proc_wfm_audio.cpp

/*
 * Copyright (C) 2014 Jared Boone, ShareBrained Technology, Inc.
 * Copyright (C) 2016 Furrtek
 *
 * This file is part of PortaPack.
 *
 * 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, 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; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

#include "proc_wfm_audio.hpp"

#include "portapack_shared_memory.hpp"
#include "audio_output.hpp"
#include "dsp_fft.hpp"
#include "event_m4.hpp"

#include <cstdint>

void WidebandFMAudio::execute(const buffer_c8_t& buffer) {
    if (!configured) {
        return;
    }

    const auto decim_0_out = decim_0.execute(buffer, dst_buffer);
    const auto channel = decim_1.execute(decim_0_out, dst_buffer);

    // TODO: Feed channel_stats post-decimation data?
    feed_channel_stats(channel);

    spectrum_samples += channel.count;
    if (spectrum_samples >= spectrum_interval_samples) {
        spectrum_samples -= spectrum_interval_samples;
        channel_spectrum.feed(channel, channel_filter_low_f, channel_filter_high_f, channel_filter_transition);
    }

    /* 384kHz complex<int16_t>[256]
     * -> FM demodulation
     * -> 384kHz int16_t[256] */
    /* TODO: To improve adjacent channel rejection, implement complex channel filter:
     *		pass < +/- 100kHz, stop > +/- 200kHz
     */

    auto audio_oversampled = demod.execute(channel, work_audio_buffer);

    /* 384kHz int16_t[256]
     * -> 4th order CIC decimation by 2, gain of 1
     * -> 192kHz int16_t[128] */
    auto audio_4fs = audio_dec_1.execute(audio_oversampled, work_audio_buffer);

    /* 192kHz int16_t[128]
     * -> 4th order CIC decimation by 2, gain of 1
     * -> 96kHz int16_t[64] */
    auto audio_2fs = audio_dec_2.execute(audio_4fs, work_audio_buffer);

    // Input: 96kHz int16_t[64]
    // audio_spectrum_decimator piles up 256 samples before doing FFT computation
    // This sends an AudioSpectrum every: sample rate/buffer size/refresh period = 3072000/2048/50 = 30 Hz
    // When audio_spectrum_timer expires, the audio spectrum computation is triggered

    // 0~3: feed continuous audio
    // 4~31: ignore, wrap at 31

    audio_spectrum_timer++;
    if (audio_spectrum_timer == 50) {
        audio_spectrum_timer = 0;
        audio_spectrum_state = FEED;
    }

    switch (audio_spectrum_state) {
        case FEED:
            // Convert audio to "complex" just so the FFT can be done :/
            for (size_t i = 0; i < 64; i++) {
                complex_audio[i] = {(int16_t)(work_audio_buffer.p[i] / 32), (int16_t)0};
            }
            audio_spectrum_decimator.feed(
                complex_audio_buffer,
                [this](const buffer_c16_t& data) {
                    this->post_message(data);
                });
            break;
        case FFT:
            // Spread the FFT workload in time to avoid making the audio skip
            // "8" comes from the log2() of the size of audio_spectrum: log2(256) = 8
            if (fft_step < 8) {
                fft_c_preswapped(audio_spectrum, fft_step, fft_step + 1);
                fft_step++;
            } else {
                const size_t spectrum_end = spectrum.db.size();
                for (size_t i = 0; i < spectrum_end; i++) {
                    // const auto corrected_sample = spectrum_window_hamming_3(audio_spectrum, i);
                    const auto corrected_sample = audio_spectrum[i];
                    const auto mag2 = magnitude_squared(corrected_sample * (1.0f / 32768.0f));
                    const float db = mag2_to_dbv_norm(mag2);
                    constexpr float mag_scale = 5.0f;
                    const unsigned int v = (db * mag_scale) + 255.0f;
                    spectrum.db[i] = std::max(0U, std::min(255U, v));
                }
                AudioSpectrumMessage message{&spectrum};
                shared_memory.application_queue.push(message);
                audio_spectrum_state = IDLE;
            }
            break;
        default:
            break;
    }

    /* 96kHz int16_t[64]
     * -> FIR filter, <15kHz (0.156fs) pass, >19kHz (0.198fs) stop, gain of 1
     * -> 48kHz int16_t[32] */
    auto audio = audio_filter.execute(audio_2fs, work_audio_buffer);

    /* -> 48kHz int16_t[32] */
    audio_output.write(audio);
}

void WidebandFMAudio::post_message(const buffer_c16_t& data) {
    // This is called when audio_spectrum_decimator is filled up to 256 samples
    fft_swap(data, audio_spectrum);
    audio_spectrum_state = FFT;
    fft_step = 0;
}

void WidebandFMAudio::on_message(const Message* const message) {
    switch (message->id) {
        case Message::ID::UpdateSpectrum:
        case Message::ID::SpectrumStreamingConfig:
            channel_spectrum.on_message(message);
            break;

        case Message::ID::WFMConfigure:
            configure(*reinterpret_cast<const WFMConfigureMessage*>(message));
            break;

        case Message::ID::CaptureConfig:
            capture_config(*reinterpret_cast<const CaptureConfigMessage*>(message));
            break;

        default:
            break;
    }
}

void WidebandFMAudio::configure(const WFMConfigureMessage& message) {
    constexpr size_t decim_0_input_fs = baseband_fs;
    constexpr size_t decim_0_output_fs = decim_0_input_fs / decim_0.decimation_factor;

    constexpr size_t decim_1_input_fs = decim_0_output_fs;
    constexpr size_t decim_1_output_fs = decim_1_input_fs / decim_1.decimation_factor;

    constexpr size_t demod_input_fs = decim_1_output_fs;

    spectrum_interval_samples = decim_1_output_fs / spectrum_rate_hz;
    spectrum_samples = 0;

    decim_0.configure(message.decim_0_filter.taps);
    decim_1.configure(message.decim_1_filter.taps);
    channel_filter_low_f = message.decim_1_filter.low_frequency_normalized * decim_1_input_fs;
    channel_filter_high_f = message.decim_1_filter.high_frequency_normalized * decim_1_input_fs;
    channel_filter_transition = message.decim_1_filter.transition_normalized * decim_1_input_fs;
    demod.configure(demod_input_fs, message.deviation);
    audio_filter.configure(message.audio_filter.taps);
    audio_output.configure(message.audio_hpf_config, message.audio_deemph_config);

    channel_spectrum.set_decimation_factor(1);

    configured = true;
}

void WidebandFMAudio::capture_config(const CaptureConfigMessage& message) {
    if (message.config) {
        audio_output.set_stream(std::make_unique<StreamInput>(message.config));
    } else {
        audio_output.set_stream(nullptr);
    }
}

int main() {
    EventDispatcher event_dispatcher{std::make_unique<WidebandFMAudio>()};
    event_dispatcher.run();
    return 0;
}