AX25Frame.cpp

/*
 *   Copyright (C) 2020 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 "Config.h"

#if defined(MODE_AX25)

#include "Globals.h"
#include "AX25Frame.h"

const uint16_t CCITT_TABLE[] = {
	0x0000,0x1189,0x2312,0x329b,0x4624,0x57ad,0x6536,0x74bf,
	0x8c48,0x9dc1,0xaf5a,0xbed3,0xca6c,0xdbe5,0xe97e,0xf8f7,
	0x1081,0x0108,0x3393,0x221a,0x56a5,0x472c,0x75b7,0x643e,
	0x9cc9,0x8d40,0xbfdb,0xae52,0xdaed,0xcb64,0xf9ff,0xe876,
	0x2102,0x308b,0x0210,0x1399,0x6726,0x76af,0x4434,0x55bd,
	0xad4a,0xbcc3,0x8e58,0x9fd1,0xeb6e,0xfae7,0xc87c,0xd9f5,
	0x3183,0x200a,0x1291,0x0318,0x77a7,0x662e,0x54b5,0x453c,
	0xbdcb,0xac42,0x9ed9,0x8f50,0xfbef,0xea66,0xd8fd,0xc974,
	0x4204,0x538d,0x6116,0x709f,0x0420,0x15a9,0x2732,0x36bb,
	0xce4c,0xdfc5,0xed5e,0xfcd7,0x8868,0x99e1,0xab7a,0xbaf3,
	0x5285,0x430c,0x7197,0x601e,0x14a1,0x0528,0x37b3,0x263a,
	0xdecd,0xcf44,0xfddf,0xec56,0x98e9,0x8960,0xbbfb,0xaa72,
	0x6306,0x728f,0x4014,0x519d,0x2522,0x34ab,0x0630,0x17b9,
	0xef4e,0xfec7,0xcc5c,0xddd5,0xa96a,0xb8e3,0x8a78,0x9bf1,
	0x7387,0x620e,0x5095,0x411c,0x35a3,0x242a,0x16b1,0x0738,
	0xffcf,0xee46,0xdcdd,0xcd54,0xb9eb,0xa862,0x9af9,0x8b70,
	0x8408,0x9581,0xa71a,0xb693,0xc22c,0xd3a5,0xe13e,0xf0b7,
	0x0840,0x19c9,0x2b52,0x3adb,0x4e64,0x5fed,0x6d76,0x7cff,
	0x9489,0x8500,0xb79b,0xa612,0xd2ad,0xc324,0xf1bf,0xe036,
	0x18c1,0x0948,0x3bd3,0x2a5a,0x5ee5,0x4f6c,0x7df7,0x6c7e,
	0xa50a,0xb483,0x8618,0x9791,0xe32e,0xf2a7,0xc03c,0xd1b5,
	0x2942,0x38cb,0x0a50,0x1bd9,0x6f66,0x7eef,0x4c74,0x5dfd,
	0xb58b,0xa402,0x9699,0x8710,0xf3af,0xe226,0xd0bd,0xc134,
	0x39c3,0x284a,0x1ad1,0x0b58,0x7fe7,0x6e6e,0x5cf5,0x4d7c,
	0xc60c,0xd785,0xe51e,0xf497,0x8028,0x91a1,0xa33a,0xb2b3,
	0x4a44,0x5bcd,0x6956,0x78df,0x0c60,0x1de9,0x2f72,0x3efb,
	0xd68d,0xc704,0xf59f,0xe416,0x90a9,0x8120,0xb3bb,0xa232,
	0x5ac5,0x4b4c,0x79d7,0x685e,0x1ce1,0x0d68,0x3ff3,0x2e7a,
	0xe70e,0xf687,0xc41c,0xd595,0xa12a,0xb0a3,0x8238,0x93b1,
	0x6b46,0x7acf,0x4854,0x59dd,0x2d62,0x3ceb,0x0e70,0x1ff9,
	0xf78f,0xe606,0xd49d,0xc514,0xb1ab,0xa022,0x92b9,0x8330,
	0x7bc7,0x6a4e,0x58d5,0x495c,0x3de3,0x2c6a,0x1ef1,0x0f78 };

CAX25Frame::CAX25Frame(const uint8_t* data, uint16_t length) :
m_data(),
m_length(0U),
m_fcs(0U)
{
  for (uint16_t i = 0U; i < length && i < (AX25_MAX_PACKET_LEN - 2U); i++)
    m_data[m_length++] = data[i];
}

CAX25Frame::CAX25Frame() :
m_data(),
m_length(0U),
m_fcs(0U)
{
}

bool CAX25Frame::append(uint16_t c)
{
  if (m_length == AX25_MAX_PACKET_LEN)
    return false;

  m_data[m_length++] = uint8_t(c);

  return true;
}

bool CAX25Frame::checkCRC()
{
  union {
    uint16_t crc16;
    uint8_t  crc8[2U];
  };

  crc16 = 0xFFFFU;
  for (uint16_t i = 0U; i < (m_length - 2U); i++)
    crc16 = uint16_t(crc8[1U]) ^ CCITT_TABLE[crc8[0U] ^ m_data[i]];

  crc16 = ~crc16;

  if (crc8[0U] == m_data[m_length - 2U] && crc8[1U] == m_data[m_length - 1U]) {
    m_fcs = crc16;
    return true;
  } else {
    return false;
  }
}

void CAX25Frame::addCRC()
{
  union {
    uint16_t crc16;
    uint8_t  crc8[2U];
  };

  crc16 = 0xFFFFU;
  for (uint16_t i = 0U; i < m_length; i++)
    crc16 = uint16_t(crc8[1U]) ^ CCITT_TABLE[crc8[0U] ^ m_data[i]];

  crc16 = ~crc16;

  m_fcs = crc16;

  m_data[m_length++] = crc8[0U];
  m_data[m_length++] = crc8[1U];
}

#endif