1 /* 2 * YAFFS: Yet another FFS. A NAND-flash specific file system. 3 * 4 * yaffs_ecc.c: ECC generation/correction algorithms. 5 * 6 * Copyright (C) 2002 Aleph One Ltd. 7 * 8 * Created by Charles Manning <charles (at) aleph1.co.uk> 9 * 10 * 11 * This program is free software; you can redistribute it and/or 12 * modify it under the terms of the GNU Lesser General Public License 13 * version 2.1 as published by the Free Software Foundation. 14 */ 15 16 /* 17 * This code implements the ECC algorithm used in SmartMedia. 18 * 19 * The ECC comprises 22 bits of parity information and is stuffed into 3 bytes. 20 * The two unused bit are set to 1. 21 * The ECC can correct single bit errors in a 256-byte page of data. Thus, two such ECC 22 * blocks are used on a 512-byte NAND page. 23 * 24 */ 25 26 /* Table generated by gen-ecc.c 27 * Using a table means we do not have to calculate p1..p4 and p1'..p4' 28 * for each byte of data. These are instead provided in a table in bits7..2. 29 * Bit 0 of each entry indicates whether the entry has an odd or even parity, and therefore 30 * this bytes influence on the line parity. 31 */ 32 33 const char *yaffs_ecc_c_version = 34 "$Id: yaffs_ecc.c,v 1.7 2006/09/14 22:02:46 charles Exp $"; 35 36 #include "yportenv.h" 37 38 #include "yaffs_ecc.h" 39 40 static const unsigned char column_parity_table[] = { 41 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69, 42 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00, 43 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc, 44 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95, 45 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0, 46 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99, 47 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65, 48 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c, 49 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc, 50 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5, 51 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59, 52 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30, 53 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55, 54 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c, 55 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0, 56 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9, 57 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0, 58 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9, 59 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55, 60 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c, 61 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59, 62 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30, 63 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc, 64 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5, 65 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65, 66 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c, 67 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0, 68 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99, 69 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc, 70 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95, 71 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69, 72 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00, 73 }; 74 75 /* Count the bits in an unsigned char or a U32 */ 76 77 static int yaffs_CountBits(unsigned char x) 78 { 79 int r = 0; 80 while (x) { 81 if (x & 1) 82 r++; 83 x >>= 1; 84 } 85 return r; 86 } 87 88 static int yaffs_CountBits32(unsigned x) 89 { 90 int r = 0; 91 while (x) { 92 if (x & 1) 93 r++; 94 x >>= 1; 95 } 96 return r; 97 } 98 99 /* Calculate the ECC for a 256-byte block of data */ 100 void yaffs_ECCCalculate(const unsigned char *data, unsigned char *ecc) 101 { 102 unsigned int i; 103 104 unsigned char col_parity = 0; 105 unsigned char line_parity = 0; 106 unsigned char line_parity_prime = 0; 107 unsigned char t; 108 unsigned char b; 109 110 for (i = 0; i < 256; i++) { 111 b = column_parity_table[*data++]; 112 col_parity ^= b; 113 114 if (b & 0x01) // odd number of bits in the byte 115 { 116 line_parity ^= i; 117 line_parity_prime ^= ~i; 118 } 119 120 } 121 122 ecc[2] = (~col_parity) | 0x03; 123 124 t = 0; 125 if (line_parity & 0x80) 126 t |= 0x80; 127 if (line_parity_prime & 0x80) 128 t |= 0x40; 129 if (line_parity & 0x40) 130 t |= 0x20; 131 if (line_parity_prime & 0x40) 132 t |= 0x10; 133 if (line_parity & 0x20) 134 t |= 0x08; 135 if (line_parity_prime & 0x20) 136 t |= 0x04; 137 if (line_parity & 0x10) 138 t |= 0x02; 139 if (line_parity_prime & 0x10) 140 t |= 0x01; 141 ecc[1] = ~t; 142 143 t = 0; 144 if (line_parity & 0x08) 145 t |= 0x80; 146 if (line_parity_prime & 0x08) 147 t |= 0x40; 148 if (line_parity & 0x04) 149 t |= 0x20; 150 if (line_parity_prime & 0x04) 151 t |= 0x10; 152 if (line_parity & 0x02) 153 t |= 0x08; 154 if (line_parity_prime & 0x02) 155 t |= 0x04; 156 if (line_parity & 0x01) 157 t |= 0x02; 158 if (line_parity_prime & 0x01) 159 t |= 0x01; 160 ecc[0] = ~t; 161 162 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER 163 // Swap the bytes into the wrong order 164 t = ecc[0]; 165 ecc[0] = ecc[1]; 166 ecc[1] = t; 167 #endif 168 } 169 170 171 /* Correct the ECC on a 256 byte block of data */ 172 173 int yaffs_ECCCorrect(unsigned char *data, unsigned char *read_ecc, 174 const unsigned char *test_ecc) 175 { 176 unsigned char d0, d1, d2; /* deltas */ 177 178 d0 = read_ecc[0] ^ test_ecc[0]; 179 d1 = read_ecc[1] ^ test_ecc[1]; 180 d2 = read_ecc[2] ^ test_ecc[2]; 181 182 if ((d0 | d1 | d2) == 0) 183 return 0; /* no error */ 184 185 if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 && 186 ((d1 ^ (d1 >> 1)) & 0x55) == 0x55 && 187 ((d2 ^ (d2 >> 1)) & 0x54) == 0x54) { 188 /* Single bit (recoverable) error in data */ 189 190 unsigned byte; 191 unsigned bit; 192 193 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER 194 // swap the bytes to correct for the wrong order 195 unsigned char t; 196 197 t = d0; 198 d0 = d1; 199 d1 = t; 200 #endif 201 202 bit = byte = 0; 203 204 if (d1 & 0x80) 205 byte |= 0x80; 206 if (d1 & 0x20) 207 byte |= 0x40; 208 if (d1 & 0x08) 209 byte |= 0x20; 210 if (d1 & 0x02) 211 byte |= 0x10; 212 if (d0 & 0x80) 213 byte |= 0x08; 214 if (d0 & 0x20) 215 byte |= 0x04; 216 if (d0 & 0x08) 217 byte |= 0x02; 218 if (d0 & 0x02) 219 byte |= 0x01; 220 221 if (d2 & 0x80) 222 bit |= 0x04; 223 if (d2 & 0x20) 224 bit |= 0x02; 225 if (d2 & 0x08) 226 bit |= 0x01; 227 228 data[byte] ^= (1 << bit); 229 230 return 1; /* Corrected the error */ 231 } 232 233 if ((yaffs_CountBits(d0) + 234 yaffs_CountBits(d1) + 235 yaffs_CountBits(d2)) == 1) { 236 /* Reccoverable error in ecc */ 237 238 read_ecc[0] = test_ecc[0]; 239 read_ecc[1] = test_ecc[1]; 240 read_ecc[2] = test_ecc[2]; 241 242 return 1; /* Corrected the error */ 243 } 244 245 /* Unrecoverable error */ 246 247 return -1; 248 249 } 250 251 252 /* 253 * ECCxxxOther does ECC calcs on arbitrary n bytes of data 254 */ 255 void yaffs_ECCCalculateOther(const unsigned char *data, unsigned nBytes, 256 yaffs_ECCOther * eccOther) 257 { 258 unsigned int i; 259 260 unsigned char col_parity = 0; 261 unsigned line_parity = 0; 262 unsigned line_parity_prime = 0; 263 unsigned char b; 264 265 for (i = 0; i < nBytes; i++) { 266 b = column_parity_table[*data++]; 267 col_parity ^= b; 268 269 if (b & 0x01) { 270 /* odd number of bits in the byte */ 271 line_parity ^= i; 272 line_parity_prime ^= ~i; 273 } 274 275 } 276 277 eccOther->colParity = (col_parity >> 2) & 0x3f; 278 eccOther->lineParity = line_parity; 279 eccOther->lineParityPrime = line_parity_prime; 280 } 281 282 int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes, 283 yaffs_ECCOther * read_ecc, 284 const yaffs_ECCOther * test_ecc) 285 { 286 unsigned char cDelta; /* column parity delta */ 287 unsigned lDelta; /* line parity delta */ 288 unsigned lDeltaPrime; /* line parity delta */ 289 unsigned bit; 290 291 cDelta = read_ecc->colParity ^ test_ecc->colParity; 292 lDelta = read_ecc->lineParity ^ test_ecc->lineParity; 293 lDeltaPrime = read_ecc->lineParityPrime ^ test_ecc->lineParityPrime; 294 295 if ((cDelta | lDelta | lDeltaPrime) == 0) 296 return 0; /* no error */ 297 298 if (lDelta == ~lDeltaPrime && 299 (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15)) 300 { 301 /* Single bit (recoverable) error in data */ 302 303 bit = 0; 304 305 if (cDelta & 0x20) 306 bit |= 0x04; 307 if (cDelta & 0x08) 308 bit |= 0x02; 309 if (cDelta & 0x02) 310 bit |= 0x01; 311 312 if(lDelta >= nBytes) 313 return -1; 314 315 data[lDelta] ^= (1 << bit); 316 317 return 1; /* corrected */ 318 } 319 320 if ((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) + 321 yaffs_CountBits(cDelta)) == 1) { 322 /* Reccoverable error in ecc */ 323 324 *read_ecc = *test_ecc; 325 return 1; /* corrected */ 326 } 327 328 /* Unrecoverable error */ 329 330 return -1; 331 332 } 333 334
