/* * * AT chat library with GLib integration * * Copyright (C) 2010 Intel Corporation. All rights reserved. * Copyright (C) 2009 Trolltech ASA. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 as * published by the Free Software Foundation. * * 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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA * */ #ifdef HAVE_CONFIG_H #include #endif #include #include #include "gsm0710.h" static const unsigned char crc_table[256] = { 0x00, 0x91, 0xE3, 0x72, 0x07, 0x96, 0xE4, 0x75, 0x0E, 0x9F, 0xED, 0x7C, 0x09, 0x98, 0xEA, 0x7B, 0x1C, 0x8D, 0xFF, 0x6E, 0x1B, 0x8A, 0xF8, 0x69, 0x12, 0x83, 0xF1, 0x60, 0x15, 0x84, 0xF6, 0x67, 0x38, 0xA9, 0xDB, 0x4A, 0x3F, 0xAE, 0xDC, 0x4D, 0x36, 0xA7, 0xD5, 0x44, 0x31, 0xA0, 0xD2, 0x43, 0x24, 0xB5, 0xC7, 0x56, 0x23, 0xB2, 0xC0, 0x51, 0x2A, 0xBB, 0xC9, 0x58, 0x2D, 0xBC, 0xCE, 0x5F, 0x70, 0xE1, 0x93, 0x02, 0x77, 0xE6, 0x94, 0x05, 0x7E, 0xEF, 0x9D, 0x0C, 0x79, 0xE8, 0x9A, 0x0B, 0x6C, 0xFD, 0x8F, 0x1E, 0x6B, 0xFA, 0x88, 0x19, 0x62, 0xF3, 0x81, 0x10, 0x65, 0xF4, 0x86, 0x17, 0x48, 0xD9, 0xAB, 0x3A, 0x4F, 0xDE, 0xAC, 0x3D, 0x46, 0xD7, 0xA5, 0x34, 0x41, 0xD0, 0xA2, 0x33, 0x54, 0xC5, 0xB7, 0x26, 0x53, 0xC2, 0xB0, 0x21, 0x5A, 0xCB, 0xB9, 0x28, 0x5D, 0xCC, 0xBE, 0x2F, 0xE0, 0x71, 0x03, 0x92, 0xE7, 0x76, 0x04, 0x95, 0xEE, 0x7F, 0x0D, 0x9C, 0xE9, 0x78, 0x0A, 0x9B, 0xFC, 0x6D, 0x1F, 0x8E, 0xFB, 0x6A, 0x18, 0x89, 0xF2, 0x63, 0x11, 0x80, 0xF5, 0x64, 0x16, 0x87, 0xD8, 0x49, 0x3B, 0xAA, 0xDF, 0x4E, 0x3C, 0xAD, 0xD6, 0x47, 0x35, 0xA4, 0xD1, 0x40, 0x32, 0xA3, 0xC4, 0x55, 0x27, 0xB6, 0xC3, 0x52, 0x20, 0xB1, 0xCA, 0x5B, 0x29, 0xB8, 0xCD, 0x5C, 0x2E, 0xBF, 0x90, 0x01, 0x73, 0xE2, 0x97, 0x06, 0x74, 0xE5, 0x9E, 0x0F, 0x7D, 0xEC, 0x99, 0x08, 0x7A, 0xEB, 0x8C, 0x1D, 0x6F, 0xFE, 0x8B, 0x1A, 0x68, 0xF9, 0x82, 0x13, 0x61, 0xF0, 0x85, 0x14, 0x66, 0xF7, 0xA8, 0x39, 0x4B, 0xDA, 0xAF, 0x3E, 0x4C, 0xDD, 0xA6, 0x37, 0x45, 0xD4, 0xA1, 0x30, 0x42, 0xD3, 0xB4, 0x25, 0x57, 0xC6, 0xB3, 0x22, 0x50, 0xC1, 0xBA, 0x2B, 0x59, 0xC8, 0xBD, 0x2C, 0x5E, 0xCF }; static inline guint8 gsm0710_crc(const guint8 *data, int len) { guint8 crc = 0xFF; int i; for (i = 0; i < len; i++) crc = crc_table[crc ^ data[i]]; return crc; } static inline guint8 gsm0710_fcs(const guint8 *data, int len) { return 0xff - gsm0710_crc(data, len); } static inline gboolean gsm0710_check_fcs(const guint8 *data, int len, guint8 cfcs) { guint8 fcs = gsm0710_crc(data, len); fcs = crc_table[fcs ^ cfcs]; if (fcs == 0xcf) return TRUE; return FALSE; } int gsm0710_advanced_extract_frame(guint8 *buf, int len, guint8 *out_dlc, guint8 *out_control, guint8 **out_frame, int *out_len) { int posn = 0; int posn2; int framelen; guint8 dlc; guint8 control; while (posn < len) { if (buf[posn] != 0x7E) { posn += 1; continue; } /* Skip additional 0x7E bytes between frames */ while ((posn + 1) < len && buf[posn + 1] == 0x7E) posn += 1; /* Search for the end of the packet (the next 0x7E byte) */ framelen = posn + 1; while (framelen < len && buf[framelen] != 0x7E) framelen += 1; if (framelen >= len) break; if (framelen < 4) { posn = framelen; continue; } /* Undo control byte quoting in the packet */ posn2 = 0; ++posn; while (posn < framelen) { if (buf[posn] == 0x7D) { ++posn; if (posn >= framelen) break; buf[posn2++] = buf[posn++] ^ 0x20; } else { buf[posn2++] = buf[posn++]; } } /* Validate the checksum on the packet header */ if (!gsm0710_check_fcs(buf, 2, buf[posn2 - 1])) continue; /* Decode and dispatch the packet */ dlc = (buf[0] >> 2) & 0x3F; control = buf[1] & 0xEF; /* Strip "PF" bit */ if (out_frame) *out_frame = buf + 2; if (out_len) *out_len = posn2 - 3; if (out_dlc) *out_dlc = dlc; if (out_control) *out_control = control; break; } return posn; } int gsm0710_advanced_fill_frame(guint8 *frame, guint8 dlc, guint8 type, const guint8 *data, int len) { int temp, crc; int size; frame[0] = 0x7E; frame[1] = ((dlc << 2) | 0x03); frame[2] = type; crc = gsm0710_fcs(frame + 1, 2); /* The Address field might need to be escaped if this is a response * frame */ /* Need to quote the type field now that crc has been computed */ if (type == 0x7E || type == 0x7D) { frame[2] = 0x7D; frame[3] = (type ^ 0x20); size = 4; } else { size = 3; } while (len > 0) { temp = *data++ & 0xFF; --len; if (temp != 0x7E && temp != 0x7D) { frame[size++] = temp; } else { frame[size++] = 0x7D; frame[size++] = (temp ^ 0x20); } } if (crc != 0x7E && crc != 0x7D) { frame[size++] = crc; } else { frame[size++] = 0x7D; frame[size++] = (crc ^ 0x20); } frame[size++] = 0x7E; return size; } int gsm0710_basic_extract_frame(guint8 *buf, int len, guint8 *out_dlc, guint8 *out_control, guint8 **out_frame, int *out_len) { int posn = 0; int framelen; int header_size; guint8 fcs; guint8 dlc; guint8 type; while (posn < len) { if (buf[posn] != 0xF9) { posn += 1; continue; } /* Skip additional 0xF9 bytes between frames */ while ((posn + 1) < len && buf[posn + 1] == 0xF9) posn += 1; /* We need at least 4 bytes for the flag + header */ if ((posn + 4) > len) break; /* The low bit of the second byte should be 1, which indicates a short channel number. According to 27.010 Section 5.2.3, if this is not true, then the frame is invalid and should be discarded */ if ((buf[posn + 1] & 0x01) == 0) { ++posn; continue; } /* Get the packet length and validate it */ framelen = buf[posn + 3] >> 1; if ((buf[posn + 3] & 0x01) != 0) { /* Single-byte length indication */ header_size = 3; } else { /* Double-byte length indication */ if ((posn + 5) > len) break; framelen |= buf[posn + 4] << 7; header_size = 4; } /* Total size of the packet is the flag + 3 or 4 byte header * Address Control Length followed by Information and FCS. * However, we must check the presence of the end flag * according to 27.010 Section 5.2.3 */ if ((posn + header_size + 3 + framelen) > len) break; fcs = buf[posn + 1 + header_size + framelen]; /* * The end flag is not guaranteed to be only ours * according to 27.010 Section 5.2.6.1: * "The closing flag may also be the opening flag of the * following frame", thus we do not consume it in the following * stages */ /* * If FCS is invalid, discard the packet in accordance to * Section 5.2.3 of 27.010 */ if (!gsm0710_check_fcs(buf + posn + 1, header_size, fcs)) { posn += header_size + framelen + 2; continue; } if (buf[posn + header_size + framelen + 2] != 0xF9) { posn += header_size + framelen + 2; continue; } /* Get the channel number and packet type from the header */ dlc = buf[posn + 1] >> 2; type = buf[posn + 2] & 0xEF; /* Strip "PF" bit */ if (out_frame) *out_frame = buf + posn + 1 + header_size; if (out_len) *out_len = framelen; if (out_dlc) *out_dlc = dlc; if (out_control) *out_control = type; posn += header_size + framelen + 2; break; } return posn; } int gsm0710_basic_fill_frame(guint8 *frame, guint8 dlc, guint8 type, const guint8 *data, int len) { int size; int header_size; frame[0] = 0xF9; frame[1] = ((dlc << 2) | 0x03); frame[2] = type; if (len <= 127) { frame[3] = ((len << 1) | 0x01); header_size = 4; } else { frame[3] = (len << 1); frame[4] = (len >> 7); header_size = 5; } size = header_size; if (len > 0) { memcpy(frame + header_size, data, len); size += len; } /* Note: GSM 07.10 says that the CRC is only computed over the header */ frame[size++] = gsm0710_fcs(frame + 1, header_size - 1); frame[size++] = 0xF9; return size; }