Holger Hans Peter Freyther | ae73a05 | 2013-05-31 09:51:53 +0200 | [diff] [blame] | 1 | /* |
| 2 | * Author: Dieter Spaar |
| 3 | * October 2012 |
| 4 | * |
| 5 | * Modified by Holger Freyther |
| 6 | */ |
| 7 | |
| 8 | #include "framing.h" |
| 9 | |
| 10 | #include <stdio.h> |
| 11 | #include <string.h> |
| 12 | |
| 13 | |
| 14 | #define PACKET_START_STOP 0x7E |
| 15 | #define PACKET_ESCAPE 0x7D |
| 16 | |
| 17 | #define CRC_SEED 0xFFFF |
| 18 | |
| 19 | /* |
| 20 | * Comment is from: utils.c of libqcdm |
| 21 | * QCDM protocol frames are pseudo Async HDLC frames which end with a 3-byte |
| 22 | * trailer. This trailer consists of the 16-bit CRC of the frame plus an ending |
| 23 | * "async control character" whose value is 0x7E. The frame *and* the CRC are |
| 24 | * escaped before adding the trailing control character so that the control |
| 25 | * character (0x7E) and the escape marker (0x7D) are never seen in the frame. |
| 26 | */ |
| 27 | |
| 28 | |
| 29 | /* 16 bit CRC, generator polynomial 0x8408 */ |
| 30 | static const uint16_t crc_ccit16[256] = |
| 31 | { |
| 32 | 0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf, |
| 33 | 0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7, |
| 34 | 0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e, |
| 35 | 0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876, |
| 36 | 0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd, |
| 37 | 0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5, |
| 38 | 0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c, |
| 39 | 0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974, |
| 40 | 0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb, |
| 41 | 0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3, |
| 42 | 0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a, |
| 43 | 0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72, |
| 44 | 0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9, |
| 45 | 0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1, |
| 46 | 0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738, |
| 47 | 0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70, |
| 48 | 0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7, |
| 49 | 0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff, |
| 50 | 0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036, |
| 51 | 0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e, |
| 52 | 0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5, |
| 53 | 0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd, |
| 54 | 0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134, |
| 55 | 0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c, |
| 56 | 0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3, |
| 57 | 0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb, |
| 58 | 0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232, |
| 59 | 0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a, |
| 60 | 0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1, |
| 61 | 0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9, |
| 62 | 0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330, |
| 63 | 0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78 |
| 64 | }; |
| 65 | |
| 66 | static uint16_t crc16(const uint8_t *data, size_t len) |
| 67 | { |
| 68 | uint16_t crc = CRC_SEED; |
| 69 | |
| 70 | for(; len != 0; len--, data++) |
| 71 | crc = crc_ccit16[(crc ^ *data) & 0x00ff] ^ (crc >> 8); |
| 72 | |
| 73 | /* return the 1's complement */ |
| 74 | return ~crc; |
| 75 | } |
| 76 | |
| 77 | #define DO_ESCAPE(x, idx, out, out_len) \ |
| 78 | if(x == PACKET_START_STOP || x == PACKET_ESCAPE) \ |
| 79 | { \ |
| 80 | if(idx + 2 > out_len) \ |
| 81 | { \ |
| 82 | printf("output buffer too small need %d have %d\n", idx + 2, out_len); \ |
| 83 | return -1; \ |
| 84 | } \ |
| 85 | out[idx++] = PACKET_ESCAPE; \ |
| 86 | out[idx++] = (x ^ 0x20); \ |
| 87 | } \ |
| 88 | else \ |
| 89 | { \ |
| 90 | if(idx + 1 > out_len) \ |
| 91 | { \ |
| 92 | printf("output buffer too small need %d have %d\n", idx + 2, out_len); \ |
| 93 | return -1; \ |
| 94 | } \ |
| 95 | out[idx++] = x; \ |
| 96 | } \ |
| 97 | |
| 98 | int frame_pack(const uint8_t *in, const size_t in_len, uint8_t *out, const size_t out_len) |
| 99 | { |
| 100 | uint8_t c; |
| 101 | size_t i, idx = 0; |
| 102 | |
| 103 | /* packet data */ |
| 104 | for (i = 0; i < in_len; i++) { |
| 105 | c = in[i]; |
| 106 | DO_ESCAPE(c, idx, out, out_len); |
| 107 | } |
| 108 | |
| 109 | /* two bytes CRC */ |
| 110 | uint16_t crc = crc16(in, in_len); |
| 111 | |
| 112 | c = (uint8_t) (crc & 0xFF); |
| 113 | DO_ESCAPE(c, idx, out, out_len); |
| 114 | |
| 115 | c = (uint8_t) (crc >> 8); |
| 116 | DO_ESCAPE(c, idx, out, out_len); |
| 117 | |
| 118 | /* end of packet */ |
| 119 | out[idx++] = PACKET_START_STOP; |
| 120 | return idx; |
| 121 | } |
| 122 | |
| 123 | #undef DO_ESCAPE |
| 124 | |
| 125 | /* returns number of bytes in pPacket if a packet is complete */ |
| 126 | int frame_unpack(uint8_t *pDataIn, int nDataIn, uint8_t *pPacket) |
| 127 | { |
| 128 | static uint8_t ubBuf[MAX_PACKET * 2]; |
| 129 | static int nDataBuf = 0; |
| 130 | int i; |
| 131 | |
| 132 | if(nDataIn > sizeof(ubBuf)) { |
| 133 | printf("Too many data\n"); |
| 134 | return -1; |
| 135 | } |
| 136 | |
| 137 | /* is there enough free space in the buffer ? */ |
| 138 | |
| 139 | if(nDataIn + nDataBuf >= sizeof(ubBuf)) { |
| 140 | /* no, empty buffer */ |
| 141 | nDataBuf = 0; |
| 142 | } |
| 143 | |
| 144 | /* append data to buffer */ |
| 145 | memcpy(ubBuf + nDataBuf, pDataIn, nDataIn); |
| 146 | nDataBuf += nDataIn; |
| 147 | |
| 148 | /* search for packet end */ |
| 149 | int idxStop = -1; |
| 150 | for (i = 0; i < nDataBuf; i++) { |
| 151 | if (ubBuf[i] == PACKET_START_STOP) { |
| 152 | idxStop = i; |
| 153 | break; |
| 154 | } |
| 155 | } |
| 156 | |
| 157 | if (idxStop < 0) |
| 158 | return 0; |
| 159 | |
| 160 | /* get packet */ |
| 161 | |
| 162 | int nDataPacket = 0; |
| 163 | int bEscape = 0; |
| 164 | for (i = 0; i < idxStop; i++) |
| 165 | { |
| 166 | if (ubBuf[i] == PACKET_ESCAPE) { |
| 167 | bEscape = 1; |
| 168 | } else { |
| 169 | if (bEscape) |
| 170 | pPacket[nDataPacket++] = (ubBuf[i] ^ 0x20); |
| 171 | else |
| 172 | pPacket[nDataPacket++] = ubBuf[i]; |
| 173 | bEscape = 0; |
| 174 | } |
| 175 | if (nDataPacket >= MAX_PACKET) { |
| 176 | printf("Too many packet data\n"); |
| 177 | return -1; |
| 178 | } |
| 179 | } |
| 180 | |
| 181 | /* remove packet from buffer */ |
| 182 | memmove(ubBuf, ubBuf + idxStop + 1, nDataBuf - (idxStop + 1)); |
| 183 | nDataBuf -= (idxStop + 1); |
| 184 | |
| 185 | /* check CRC */ |
| 186 | |
| 187 | if (nDataPacket <= 2) { |
| 188 | printf("Not enough packet data\n"); |
| 189 | return -1; |
| 190 | } |
| 191 | |
| 192 | uint16_t crc = crc16(pPacket, nDataPacket - 2); |
| 193 | if((crc & 0xFF) != pPacket[nDataPacket - 2] || |
| 194 | (crc >> 8) != pPacket[nDataPacket - 1]) { |
| 195 | printf("Invalid CRC (0x%04X != 0x%02X%02X)\n", |
| 196 | crc, pPacket[nDataPacket - 1], pPacket[nDataPacket - 2]); |
| 197 | return -1; |
| 198 | } |
| 199 | |
| 200 | return nDataPacket - 2; |
| 201 | } |