1 /* 2 * YAFFS: Yet Another Flash File System. A NAND-flash specific file system. 3 * 4 * Copyright (C) 2002-2007 Aleph One Ltd. 5 * for Toby Churchill Ltd and Brightstar Engineering 6 * 7 * Created by Charles Manning <charles@aleph1.co.uk> 8 * 9 * This program is free software; you can redistribute it and/or modify 10 * it under the terms of the GNU General Public License version 2 as 11 * published by the Free Software Foundation. 12 */ 13 14 /* 15 * This code implements the ECC algorithm used in SmartMedia. 16 * 17 * The ECC comprises 22 bits of parity information and is stuffed into 3 bytes. 18 * The two unused bit are set to 1. 19 * The ECC can correct single bit errors in a 256-byte page of data. Thus, two such ECC 20 * blocks are used on a 512-byte NAND page. 21 * 22 */ 23 24 /* Table generated by gen-ecc.c 25 * Using a table means we do not have to calculate p1..p4 and p1'..p4' 26 * for each byte of data. These are instead provided in a table in bits7..2. 27 * Bit 0 of each entry indicates whether the entry has an odd or even parity, and therefore 28 * this bytes influence on the line parity. 29 */ 30 31 const char *yaffs_ecc_c_version = 32 "$Id: yaffs_ecc.c,v 1.9 2007/02/14 01:09:06 wookey Exp $"; 33 34 #include "yportenv.h" 35 36 #include "yaffs_ecc.h" 37 38 static const unsigned char column_parity_table[] = { 39 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69, 40 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00, 41 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc, 42 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95, 43 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0, 44 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99, 45 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65, 46 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c, 47 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc, 48 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5, 49 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59, 50 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30, 51 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55, 52 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c, 53 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0, 54 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9, 55 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0, 56 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9, 57 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55, 58 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c, 59 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59, 60 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30, 61 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc, 62 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5, 63 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65, 64 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c, 65 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0, 66 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99, 67 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc, 68 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95, 69 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69, 70 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00, 71 }; 72 73 /* Count the bits in an unsigned char or a U32 */ 74 75 static int yaffs_CountBits(unsigned char x) 76 { 77 int r = 0; 78 while (x) { 79 if (x & 1) 80 r++; 81 x >>= 1; 82 } 83 return r; 84 } 85 86 static int yaffs_CountBits32(unsigned x) 87 { 88 int r = 0; 89 while (x) { 90 if (x & 1) 91 r++; 92 x >>= 1; 93 } 94 return r; 95 } 96 97 /* Calculate the ECC for a 256-byte block of data */ 98 void yaffs_ECCCalculate(const unsigned char *data, unsigned char *ecc) 99 { 100 unsigned int i; 101 102 unsigned char col_parity = 0; 103 unsigned char line_parity = 0; 104 unsigned char line_parity_prime = 0; 105 unsigned char t; 106 unsigned char b; 107 108 for (i = 0; i < 256; i++) { 109 b = column_parity_table[*data++]; 110 col_parity ^= b; 111 112 if (b & 0x01) // odd number of bits in the byte 113 { 114 line_parity ^= i; 115 line_parity_prime ^= ~i; 116 } 117 118 } 119 120 ecc[2] = (~col_parity) | 0x03; 121 122 t = 0; 123 if (line_parity & 0x80) 124 t |= 0x80; 125 if (line_parity_prime & 0x80) 126 t |= 0x40; 127 if (line_parity & 0x40) 128 t |= 0x20; 129 if (line_parity_prime & 0x40) 130 t |= 0x10; 131 if (line_parity & 0x20) 132 t |= 0x08; 133 if (line_parity_prime & 0x20) 134 t |= 0x04; 135 if (line_parity & 0x10) 136 t |= 0x02; 137 if (line_parity_prime & 0x10) 138 t |= 0x01; 139 ecc[1] = ~t; 140 141 t = 0; 142 if (line_parity & 0x08) 143 t |= 0x80; 144 if (line_parity_prime & 0x08) 145 t |= 0x40; 146 if (line_parity & 0x04) 147 t |= 0x20; 148 if (line_parity_prime & 0x04) 149 t |= 0x10; 150 if (line_parity & 0x02) 151 t |= 0x08; 152 if (line_parity_prime & 0x02) 153 t |= 0x04; 154 if (line_parity & 0x01) 155 t |= 0x02; 156 if (line_parity_prime & 0x01) 157 t |= 0x01; 158 ecc[0] = ~t; 159 160 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER 161 // Swap the bytes into the wrong order 162 t = ecc[0]; 163 ecc[0] = ecc[1]; 164 ecc[1] = t; 165 #endif 166 } 167 168 169 /* Correct the ECC on a 256 byte block of data */ 170 171 int yaffs_ECCCorrect(unsigned char *data, unsigned char *read_ecc, 172 const unsigned char *test_ecc) 173 { 174 unsigned char d0, d1, d2; /* deltas */ 175 176 d0 = read_ecc[0] ^ test_ecc[0]; 177 d1 = read_ecc[1] ^ test_ecc[1]; 178 d2 = read_ecc[2] ^ test_ecc[2]; 179 180 if ((d0 | d1 | d2) == 0) 181 return 0; /* no error */ 182 183 if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 && 184 ((d1 ^ (d1 >> 1)) & 0x55) == 0x55 && 185 ((d2 ^ (d2 >> 1)) & 0x54) == 0x54) { 186 /* Single bit (recoverable) error in data */ 187 188 unsigned byte; 189 unsigned bit; 190 191 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER 192 // swap the bytes to correct for the wrong order 193 unsigned char t; 194 195 t = d0; 196 d0 = d1; 197 d1 = t; 198 #endif 199 200 bit = byte = 0; 201 202 if (d1 & 0x80) 203 byte |= 0x80; 204 if (d1 & 0x20) 205 byte |= 0x40; 206 if (d1 & 0x08) 207 byte |= 0x20; 208 if (d1 & 0x02) 209 byte |= 0x10; 210 if (d0 & 0x80) 211 byte |= 0x08; 212 if (d0 & 0x20) 213 byte |= 0x04; 214 if (d0 & 0x08) 215 byte |= 0x02; 216 if (d0 & 0x02) 217 byte |= 0x01; 218 219 if (d2 & 0x80) 220 bit |= 0x04; 221 if (d2 & 0x20) 222 bit |= 0x02; 223 if (d2 & 0x08) 224 bit |= 0x01; 225 226 data[byte] ^= (1 << bit); 227 228 return 1; /* Corrected the error */ 229 } 230 231 if ((yaffs_CountBits(d0) + 232 yaffs_CountBits(d1) + 233 yaffs_CountBits(d2)) == 1) { 234 /* Reccoverable error in ecc */ 235 236 read_ecc[0] = test_ecc[0]; 237 read_ecc[1] = test_ecc[1]; 238 read_ecc[2] = test_ecc[2]; 239 240 return 1; /* Corrected the error */ 241 } 242 243 /* Unrecoverable error */ 244 245 return -1; 246 247 } 248 249 250 /* 251 * ECCxxxOther does ECC calcs on arbitrary n bytes of data 252 */ 253 void yaffs_ECCCalculateOther(const unsigned char *data, unsigned nBytes, 254 yaffs_ECCOther * eccOther) 255 { 256 unsigned int i; 257 258 unsigned char col_parity = 0; 259 unsigned line_parity = 0; 260 unsigned line_parity_prime = 0; 261 unsigned char b; 262 263 for (i = 0; i < nBytes; i++) { 264 b = column_parity_table[*data++]; 265 col_parity ^= b; 266 267 if (b & 0x01) { 268 /* odd number of bits in the byte */ 269 line_parity ^= i; 270 line_parity_prime ^= ~i; 271 } 272 273 } 274 275 eccOther->colParity = (col_parity >> 2) & 0x3f; 276 eccOther->lineParity = line_parity; 277 eccOther->lineParityPrime = line_parity_prime; 278 } 279 280 int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes, 281 yaffs_ECCOther * read_ecc, 282 const yaffs_ECCOther * test_ecc) 283 { 284 unsigned char cDelta; /* column parity delta */ 285 unsigned lDelta; /* line parity delta */ 286 unsigned lDeltaPrime; /* line parity delta */ 287 unsigned bit; 288 289 cDelta = read_ecc->colParity ^ test_ecc->colParity; 290 lDelta = read_ecc->lineParity ^ test_ecc->lineParity; 291 lDeltaPrime = read_ecc->lineParityPrime ^ test_ecc->lineParityPrime; 292 293 if ((cDelta | lDelta | lDeltaPrime) == 0) 294 return 0; /* no error */ 295 296 if (lDelta == ~lDeltaPrime && 297 (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15)) 298 { 299 /* Single bit (recoverable) error in data */ 300 301 bit = 0; 302 303 if (cDelta & 0x20) 304 bit |= 0x04; 305 if (cDelta & 0x08) 306 bit |= 0x02; 307 if (cDelta & 0x02) 308 bit |= 0x01; 309 310 if(lDelta >= nBytes) 311 return -1; 312 313 data[lDelta] ^= (1 << bit); 314 315 return 1; /* corrected */ 316 } 317 318 if ((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) + 319 yaffs_CountBits(cDelta)) == 1) { 320 /* Reccoverable error in ecc */ 321 322 *read_ecc = *test_ecc; 323 return 1; /* corrected */ 324 } 325 326 /* Unrecoverable error */ 327 328 return -1; 329 330 } 331 332