1/* 2 * YAFFS: Yet Another Flash File System. A NAND-flash specific file system. 3 * 4 * Copyright (C) 2002-2010 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#include "yportenv.h" 32 33#include "yaffs_ecc.h" 34 35static const unsigned char column_parity_table[] = { 36 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69, 37 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00, 38 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc, 39 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95, 40 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0, 41 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99, 42 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65, 43 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c, 44 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc, 45 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5, 46 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59, 47 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30, 48 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55, 49 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c, 50 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0, 51 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9, 52 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0, 53 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9, 54 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55, 55 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c, 56 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59, 57 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30, 58 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc, 59 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5, 60 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65, 61 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c, 62 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0, 63 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99, 64 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc, 65 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95, 66 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69, 67 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00, 68}; 69 70/* Count the bits in an unsigned char or a U32 */ 71 72static int yaffs_count_bits(unsigned char x) 73{ 74 int r = 0; 75 while (x) { 76 if (x & 1) 77 r++; 78 x >>= 1; 79 } 80 return r; 81} 82 83static int yaffs_count_bits32(unsigned x) 84{ 85 int r = 0; 86 while (x) { 87 if (x & 1) 88 r++; 89 x >>= 1; 90 } 91 return r; 92} 93 94/* Calculate the ECC for a 256-byte block of data */ 95void yaffs_ecc_cacl(const unsigned char *data, unsigned char *ecc) 96{ 97 unsigned int i; 98 99 unsigned char col_parity = 0; 100 unsigned char line_parity = 0; 101 unsigned char line_parity_prime = 0; 102 unsigned char t; 103 unsigned char b; 104 105 for (i = 0; i < 256; i++) { 106 b = column_parity_table[*data++]; 107 col_parity ^= b; 108 109 if (b & 0x01) { /* odd number of bits in the byte */ 110 line_parity ^= i; 111 line_parity_prime ^= ~i; 112 } 113 } 114 115 ecc[2] = (~col_parity) | 0x03; 116 117 t = 0; 118 if (line_parity & 0x80) 119 t |= 0x80; 120 if (line_parity_prime & 0x80) 121 t |= 0x40; 122 if (line_parity & 0x40) 123 t |= 0x20; 124 if (line_parity_prime & 0x40) 125 t |= 0x10; 126 if (line_parity & 0x20) 127 t |= 0x08; 128 if (line_parity_prime & 0x20) 129 t |= 0x04; 130 if (line_parity & 0x10) 131 t |= 0x02; 132 if (line_parity_prime & 0x10) 133 t |= 0x01; 134 ecc[1] = ~t; 135 136 t = 0; 137 if (line_parity & 0x08) 138 t |= 0x80; 139 if (line_parity_prime & 0x08) 140 t |= 0x40; 141 if (line_parity & 0x04) 142 t |= 0x20; 143 if (line_parity_prime & 0x04) 144 t |= 0x10; 145 if (line_parity & 0x02) 146 t |= 0x08; 147 if (line_parity_prime & 0x02) 148 t |= 0x04; 149 if (line_parity & 0x01) 150 t |= 0x02; 151 if (line_parity_prime & 0x01) 152 t |= 0x01; 153 ecc[0] = ~t; 154 155#ifdef CONFIG_YAFFS_ECC_WRONG_ORDER 156 /* Swap the bytes into the wrong order */ 157 t = ecc[0]; 158 ecc[0] = ecc[1]; 159 ecc[1] = t; 160#endif 161} 162 163 164/* Correct the ECC on a 256 byte block of data */ 165 166int yaffs_ecc_correct(unsigned char *data, unsigned char *read_ecc, 167 const unsigned char *test_ecc) 168{ 169 unsigned char d0, d1, d2; /* deltas */ 170 171 d0 = read_ecc[0] ^ test_ecc[0]; 172 d1 = read_ecc[1] ^ test_ecc[1]; 173 d2 = read_ecc[2] ^ test_ecc[2]; 174 175 if ((d0 | d1 | d2) == 0) 176 return 0; /* no error */ 177 178 if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 && 179 ((d1 ^ (d1 >> 1)) & 0x55) == 0x55 && 180 ((d2 ^ (d2 >> 1)) & 0x54) == 0x54) { 181 /* Single bit (recoverable) error in data */ 182 183 unsigned byte; 184 unsigned bit; 185 186#ifdef CONFIG_YAFFS_ECC_WRONG_ORDER 187 /* swap the bytes to correct for the wrong order */ 188 unsigned char t; 189 190 t = d0; 191 d0 = d1; 192 d1 = t; 193#endif 194 195 bit = byte = 0; 196 197 if (d1 & 0x80) 198 byte |= 0x80; 199 if (d1 & 0x20) 200 byte |= 0x40; 201 if (d1 & 0x08) 202 byte |= 0x20; 203 if (d1 & 0x02) 204 byte |= 0x10; 205 if (d0 & 0x80) 206 byte |= 0x08; 207 if (d0 & 0x20) 208 byte |= 0x04; 209 if (d0 & 0x08) 210 byte |= 0x02; 211 if (d0 & 0x02) 212 byte |= 0x01; 213 214 if (d2 & 0x80) 215 bit |= 0x04; 216 if (d2 & 0x20) 217 bit |= 0x02; 218 if (d2 & 0x08) 219 bit |= 0x01; 220 221 data[byte] ^= (1 << bit); 222 223 return 1; /* Corrected the error */ 224 } 225 226 if ((yaffs_count_bits(d0) + 227 yaffs_count_bits(d1) + 228 yaffs_count_bits(d2)) == 1) { 229 /* Reccoverable error in ecc */ 230 231 read_ecc[0] = test_ecc[0]; 232 read_ecc[1] = test_ecc[1]; 233 read_ecc[2] = test_ecc[2]; 234 235 return 1; /* Corrected the error */ 236 } 237 238 /* Unrecoverable error */ 239 240 return -1; 241 242} 243 244 245/* 246 * ECCxxxOther does ECC calcs on arbitrary n bytes of data 247 */ 248void yaffs_ecc_calc_other(const unsigned char *data, unsigned n_bytes, 249 yaffs_ECCOther *eccOther) 250{ 251 unsigned int i; 252 253 unsigned char col_parity = 0; 254 unsigned line_parity = 0; 255 unsigned line_parity_prime = 0; 256 unsigned char b; 257 258 for (i = 0; i < n_bytes; i++) { 259 b = column_parity_table[*data++]; 260 col_parity ^= b; 261 262 if (b & 0x01) { 263 /* odd number of bits in the byte */ 264 line_parity ^= i; 265 line_parity_prime ^= ~i; 266 } 267 268 } 269 270 eccOther->colParity = (col_parity >> 2) & 0x3f; 271 eccOther->lineParity = line_parity; 272 eccOther->lineParityPrime = line_parity_prime; 273} 274 275int yaffs_ecc_correct_other(unsigned char *data, unsigned n_bytes, 276 yaffs_ECCOther *read_ecc, 277 const yaffs_ECCOther *test_ecc) 278{ 279 unsigned char cDelta; /* column parity delta */ 280 unsigned lDelta; /* line parity delta */ 281 unsigned lDeltaPrime; /* line parity delta */ 282 unsigned bit; 283 284 cDelta = read_ecc->colParity ^ test_ecc->colParity; 285 lDelta = read_ecc->lineParity ^ test_ecc->lineParity; 286 lDeltaPrime = read_ecc->lineParityPrime ^ test_ecc->lineParityPrime; 287 288 if ((cDelta | lDelta | lDeltaPrime) == 0) 289 return 0; /* no error */ 290 291 if (lDelta == ~lDeltaPrime && 292 (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15)) { 293 /* Single bit (recoverable) error in data */ 294 295 bit = 0; 296 297 if (cDelta & 0x20) 298 bit |= 0x04; 299 if (cDelta & 0x08) 300 bit |= 0x02; 301 if (cDelta & 0x02) 302 bit |= 0x01; 303 304 if (lDelta >= n_bytes) 305 return -1; 306 307 data[lDelta] ^= (1 << bit); 308 309 return 1; /* corrected */ 310 } 311 312 if ((yaffs_count_bits32(lDelta) + yaffs_count_bits32(lDeltaPrime) + 313 yaffs_count_bits(cDelta)) == 1) { 314 /* Reccoverable error in ecc */ 315 316 *read_ecc = *test_ecc; 317 return 1; /* corrected */ 318 } 319 320 /* Unrecoverable error */ 321 322 return -1; 323} 324