mayhem-firmware/firmware/application/protocols/ax25.cpp

/*
 * Copyright (C) 2014 Jared Boone, ShareBrained Technology, Inc.
 * Copyright (C) 2017 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 "ax25.hpp"

#include "portapack_shared_memory.hpp"

namespace ax25 {

void AX25Frame::make_extended_field(char* const data, size_t length, bool is_last) {
    size_t i = 0;

    for (i = 0; i < length - 1; i++)
        add_data(data[i] << 1);

    if (is_last)
        add_data((data[i] << 1) | 1);
    else
        add_data((data[i] << 1));
}

void AX25Frame::NRZI_add_bit(const uint32_t bit) {
    if (!bit)
        current_bit ^= 1;  // Zero: flip

    current_byte <<= 1;
    current_byte |= current_bit;

    bit_counter++;

    if (bit_counter == 8) {
        bit_counter = 0;
        *bb_data_ptr = current_byte;
        bb_data_ptr++;
    }
}

void AX25Frame::add_byte(uint8_t byte, bool is_flag, bool is_data) {
    bool bit;

    if (is_data)
        crc_ccitt.process_byte(byte);

    for (uint32_t i = 0; i < 8; i++) {
        bit = (byte >> i) & 1;

        NRZI_add_bit(bit);

        if (bit) {
            ones_counter++;
            if ((ones_counter == 5) && (!is_flag)) {
                NRZI_add_bit(0);
                ones_counter = 0;
            }
        } else
            ones_counter = 0;
    }
}

void AX25Frame::flush() {
    if (bit_counter)
        *bb_data_ptr = current_byte << (8 - bit_counter);  // euquiq: This was 7 but there are 8 bits
};

void AX25Frame::add_flag() {
    add_byte(AX25_FLAG, true, false);
};

void AX25Frame::add_data(uint8_t byte) {
    add_byte(byte, false, true);
};

void AX25Frame::add_checksum() {
    auto checksum = crc_ccitt.checksum();
    add_byte(checksum, false, false);
    add_byte(checksum >> 8, false, false);
}

void AX25Frame::make_ui_frame(char* const address, const uint8_t control, const uint8_t protocol, const std::string& info, const std::string& path) {
    size_t i;

    bb_data_ptr = (uint16_t*)shared_memory.bb_data.data;
    memset(bb_data_ptr, 0, sizeof(shared_memory.bb_data.data));
    bit_counter = 0;
    current_bit = 0;
    current_byte = 0;
    ones_counter = 0;
    crc_ccitt.reset();

    add_flag();  // 0x73
    add_flag();  // 0x73
    add_flag();  // 0x73
    add_flag();  // 0x73

    // path must not contain the - character! just the callsign and SSID next to each other
    bool has_path = (path.size() > 0 && path.size() <= 63 && path.size() % 7 == 0);
    make_extended_field(address, 14, !has_path);
    if (has_path) {
        make_extended_field(const_cast<char*>(path.data()), path.size(), true);
    }
    add_data(control);   // 0x03
    add_data(protocol);  // 0xf0

    for (i = 0; i < info.size(); i++)
        add_data(info[i]);

    add_checksum();  // fcs

    add_flag();  // 0x73
    add_flag();  // 0x73

    flush();
}

// __attribute__((used)) prevents dead-stripping; called only from KISS TNC external app.
__attribute__((used)) void AX25Frame::make_frame_from_raw(const uint8_t* data, size_t len) {
    bb_data_ptr = (uint16_t*)shared_memory.bb_data.data;
    memset(bb_data_ptr, 0, sizeof(shared_memory.bb_data.data));
    bit_counter = 0;
    current_bit = 0;
    current_byte = 0;
    ones_counter = 0;
    crc_ccitt.reset();

    add_flag();
    add_flag();
    add_flag();
    add_flag();

    for (size_t i = 0; i < len; i++)
        add_data(data[i]);

    add_checksum();

    add_flag();
    add_flag();

    flush();
}

} /* namespace ax25 */