mayhem-firmware/firmware/baseband/proc_aprsrx.cpp

/*
 * Copyright (C) 2015 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_aprsrx.hpp"
#include "portapack_shared_memory.hpp"

#include "event_m4.hpp"

#include "stdio.h"

void APRSRxProcessor::execute(const buffer_c8_t& buffer) {
    // This is called at 3072000 / 2048 = 1500Hz

    if (!configured) return;

    // FM demodulation
    const auto decim_0_out = decim_0.execute(buffer, dst_buffer);              // 2048 / 8 = 256 (512 I/Q samples)
    const auto decim_1_out = decim_1.execute(decim_0_out, dst_buffer);         // 256 / 8 = 32 (64 I/Q samples)
    const auto channel_out = channel_filter.execute(decim_1_out, dst_buffer);  // 32 / 2 = 16 (32 I/Q samples)

    feed_channel_stats(channel_out);

    auto audio = demod.execute(channel_out, audio_buffer);

    audio_output.write(audio);

    // Audio signal processing
    for (size_t c = 0; c < audio.count; c++) {
        const int32_t sample_int = audio.p[c] * 32768.0f;
        int32_t current_sample = __SSAT(sample_int, 16);

        current_sample /= 128;

        // Delay line put
        delay_line[delay_line_index & 0x3F] = current_sample;

        // Delay line get, and LPF
        sample_mixed = (delay_line[(delay_line_index - (samples_per_bit / 2)) & 0x3F] * current_sample) / 4;
        sample_filtered = prev_mixed + sample_mixed + (prev_filtered / 2);

        delay_line_index++;

        prev_filtered = sample_filtered;
        prev_mixed = sample_mixed;

        // Slice
        sample_bits <<= 1;

        uint8_t bit = (sample_filtered < -20) ? 1 : 0;
        sample_bits |= bit;

        /*
                int16_t scaled = bit == 1 ? 32767 : -32767;

                if( stream ) {
                        const size_t bytes_to_write = sizeof(scaled) * 1;
                        const auto result = stream->write(&scaled, bytes_to_write);
                }
*/

        // Check for "clean" transition: either 0011 or 1100
        if ((((sample_bits >> 2) ^ sample_bits) & 3) == 3) {
            // Adjust phase
            if (phase < 0x8000)
                phase += 0x800;  // Is this a proper value ?
            else
                phase -= 0x800;
        }

        phase += phase_inc;

        if (phase >= 0x10000) {
            phase &= 0xFFFF;

            if (true) {
                uint8_t bit;
                if (__builtin_popcount(sample_bits & 0xFF) >= 0x05) {
                    bit = 0x1;
                } else {
                    bit = 0x0;
                }

                if (parse_bit(bit)) {
                    parse_packet();
                }
            }
        }
    }
}

void APRSRxProcessor::parse_packet() {
    // validate crc
    if (packet_buffer_size >= aprs::APRS_MIN_LENGTH) {
        uint16_t crc = 0xFFFF;

        for (size_t i = 0; i < packet_buffer_size; i++) {
            uint8_t byte = packet_buffer[i];
            crc = ((crc >> 8) ^ crc_ccitt_tab[(crc ^ byte) & 0xFF]) & 0xFFFF;
        }

        if (crc == 0xF0B8) {
            parse_ax25();
        }
    }
}

void APRSRxProcessor::parse_ax25() {
    aprs_packet.clear();
    aprs_packet.set_valid_checksum(true);

    for (size_t i = 0; i < packet_buffer_size; i++) {
        aprs_packet.set(i, packet_buffer[i]);
    }

    APRSPacketMessage packet_message{aprs_packet};
    shared_memory.application_queue.push(packet_message);
}

bool APRSRxProcessor::parse_bit(const uint8_t current_bit) {
    uint8_t decoded_bit = ~(current_bit ^ last_bit) & 0x1;
    last_bit = current_bit;

    // int16_t log = decoded_bit == 0 ? -32768 : 32767;
    // if(stream){
    //     const size_t bytes_to_write = sizeof(log) * 1;
    //     const auto result = stream->write(&log, bytes_to_write);
    // }

    if (decoded_bit & 0x1) {
        if (ones_count < 8) {
            ones_count++;
        }
    } else {
        if (ones_count > 6) {  // not valid
            state = WAIT_FLAG;
            current_byte = 0;
            ones_count = 0;
            byte_index = 0;
            packet_buffer_size = 0;
            return false;
        } else if (ones_count == 6) {  // flag
            bool done = false;
            if (state == IN_FRAME) {
                done = true;
            } else {
                packet_buffer_size = 0;
            }
            state = WAIT_FRAME;
            current_byte = 0;
            ones_count = 0;
            byte_index = 0;

            return done;
        } else if (ones_count == 5) {  // bit stuff
            ones_count = 0;
            return false;
        } else {
            ones_count = 0;
        }
    }

    // store
    current_byte = current_byte >> 1;
    current_byte |= (decoded_bit == 0x1 ? 0x80 : 0x0);
    byte_index++;

    if (byte_index >= 8) {
        byte_index = 0;
        if (state == WAIT_FRAME) {
            state = IN_FRAME;
        }

        if (state == IN_FRAME) {
            if (packet_buffer_size + 1 >= 256) {
                state = WAIT_FLAG;
                current_byte = 0;
                ones_count = 0;
                byte_index = 0;
                packet_buffer_size = 0;
                return false;
            }
            packet_buffer[packet_buffer_size++] = current_byte;
        }
    }

    return false;
}

void APRSRxProcessor::on_message(const Message* const message) {
    if (message->id == Message::ID::APRSRxConfigure)
        configure(*reinterpret_cast<const APRSRxConfigureMessage*>(message));
    if (message->id == Message::ID::CaptureConfig)
        capture_config(*reinterpret_cast<const CaptureConfigMessage*>(message));
}

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

void APRSRxProcessor::configure(const APRSRxConfigureMessage& message) {
    decim_0.configure(taps_11k0_decim_0.taps);
    decim_1.configure(taps_11k0_decim_1.taps);
    channel_filter.configure(taps_11k0_channel.taps, 2);
    demod.configure(audio_fs, 5000);

    audio_output.configure(audio_24k_hpf_300hz_config, audio_24k_deemph_300_6_config, 0);

    samples_per_bit = audio_fs / message.baudrate;

    phase_inc = (0x10000 * message.baudrate) / audio_fs;
    phase = 0;

    // Delay line
    delay_line_index = 0;

    state = WAIT_FLAG;

    configured = true;
}

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