portapack-mayhem/firmware/application/protocols/ax25.cpp
2017-05-25 21:08:33 +01:00

121 lines
2.6 KiB
C++

/*
* 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) {
size_t i = 0;
for (i = 0; i < length - 1; i++)
add_data(data[i] << 1);
add_data((data[i] << 1) | 1);
}
void AX25Frame::add_byte(uint8_t byte, bool is_flag, bool is_data) {
size_t i;
for (i = 0; i < 8; ) {
if (!(byte & 1)) {
current_bit ^= 1; // Zero: flip
ones_counter = 0;
byte >>= 1;
i++;
} else {
ones_counter++;
if ((ones_counter == 5) && (!is_flag)) {
current_bit ^= 1; // Stuff zero: flip
ones_counter = 0;
} else {
byte >>= 1;
i++;
}
}
if (is_data)
crc_ccitt.process_bit(current_bit);
current_byte <<= 1;
current_byte |= current_bit;
if (bit_counter == 7) {
bit_counter = 0;
*bb_data_ptr = current_byte;
bb_data_ptr++;
} else {
bit_counter++;
}
}
}
void AX25Frame::flush() {
if (bit_counter)
*bb_data_ptr = current_byte << (7 - bit_counter);
};
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 >> 8, false, false);
add_byte(checksum, false, false);
}
void AX25Frame::make_ui_frame(char * const address, const uint8_t control,
const uint8_t protocol, uint8_t * const info, size_t length) {
size_t i;
bb_data_ptr = shared_memory.bb_data.data;
bit_counter = 0;
current_bit = 0;
current_byte = 0;
ones_counter = 0;
crc_ccitt.reset();
add_flag();
make_extended_field(address, 14);
add_data(control);
add_data(protocol);
for (i = 0; i < length; i++)
add_data(info[i]);
add_checksum();
add_flag();
flush();
}
} /* namespace ax25 */