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 /* XXX U-BOOT XXX */ 32 #include <common.h> 33 34 const char *yaffs_ecc_c_version = 35 "$Id: yaffs_ecc.c,v 1.9 2007/02/14 01:09:06 wookey Exp $"; 36 37 #include "yportenv.h" 38 39 #include "yaffs_ecc.h" 40 41 static const unsigned char column_parity_table[] = { 42 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69, 43 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00, 44 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc, 45 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95, 46 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0, 47 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99, 48 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65, 49 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c, 50 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc, 51 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5, 52 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59, 53 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30, 54 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55, 55 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c, 56 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0, 57 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9, 58 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0, 59 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9, 60 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55, 61 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c, 62 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59, 63 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30, 64 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc, 65 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5, 66 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65, 67 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c, 68 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0, 69 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99, 70 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc, 71 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95, 72 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69, 73 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00, 74 }; 75 76 /* Count the bits in an unsigned char or a U32 */ 77 78 static int yaffs_CountBits(unsigned char x) 79 { 80 int r = 0; 81 while (x) { 82 if (x & 1) 83 r++; 84 x >>= 1; 85 } 86 return r; 87 } 88 89 static int yaffs_CountBits32(unsigned x) 90 { 91 int r = 0; 92 while (x) { 93 if (x & 1) 94 r++; 95 x >>= 1; 96 } 97 return r; 98 } 99 100 /* Calculate the ECC for a 256-byte block of data */ 101 void yaffs_ECCCalculate(const unsigned char *data, unsigned char *ecc) 102 { 103 unsigned int i; 104 105 unsigned char col_parity = 0; 106 unsigned char line_parity = 0; 107 unsigned char line_parity_prime = 0; 108 unsigned char t; 109 unsigned char b; 110 111 for (i = 0; i < 256; i++) { 112 b = column_parity_table[*data++]; 113 col_parity ^= b; 114 115 if (b & 0x01) // odd number of bits in the byte 116 { 117 line_parity ^= i; 118 line_parity_prime ^= ~i; 119 } 120 121 } 122 123 ecc[2] = (~col_parity) | 0x03; 124 125 t = 0; 126 if (line_parity & 0x80) 127 t |= 0x80; 128 if (line_parity_prime & 0x80) 129 t |= 0x40; 130 if (line_parity & 0x40) 131 t |= 0x20; 132 if (line_parity_prime & 0x40) 133 t |= 0x10; 134 if (line_parity & 0x20) 135 t |= 0x08; 136 if (line_parity_prime & 0x20) 137 t |= 0x04; 138 if (line_parity & 0x10) 139 t |= 0x02; 140 if (line_parity_prime & 0x10) 141 t |= 0x01; 142 ecc[1] = ~t; 143 144 t = 0; 145 if (line_parity & 0x08) 146 t |= 0x80; 147 if (line_parity_prime & 0x08) 148 t |= 0x40; 149 if (line_parity & 0x04) 150 t |= 0x20; 151 if (line_parity_prime & 0x04) 152 t |= 0x10; 153 if (line_parity & 0x02) 154 t |= 0x08; 155 if (line_parity_prime & 0x02) 156 t |= 0x04; 157 if (line_parity & 0x01) 158 t |= 0x02; 159 if (line_parity_prime & 0x01) 160 t |= 0x01; 161 ecc[0] = ~t; 162 163 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER 164 // Swap the bytes into the wrong order 165 t = ecc[0]; 166 ecc[0] = ecc[1]; 167 ecc[1] = t; 168 #endif 169 } 170 171 172 /* Correct the ECC on a 256 byte block of data */ 173 174 int yaffs_ECCCorrect(unsigned char *data, unsigned char *read_ecc, 175 const unsigned char *test_ecc) 176 { 177 unsigned char d0, d1, d2; /* deltas */ 178 179 d0 = read_ecc[0] ^ test_ecc[0]; 180 d1 = read_ecc[1] ^ test_ecc[1]; 181 d2 = read_ecc[2] ^ test_ecc[2]; 182 183 if ((d0 | d1 | d2) == 0) 184 return 0; /* no error */ 185 186 if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 && 187 ((d1 ^ (d1 >> 1)) & 0x55) == 0x55 && 188 ((d2 ^ (d2 >> 1)) & 0x54) == 0x54) { 189 /* Single bit (recoverable) error in data */ 190 191 unsigned byte; 192 unsigned bit; 193 194 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER 195 // swap the bytes to correct for the wrong order 196 unsigned char t; 197 198 t = d0; 199 d0 = d1; 200 d1 = t; 201 #endif 202 203 bit = byte = 0; 204 205 if (d1 & 0x80) 206 byte |= 0x80; 207 if (d1 & 0x20) 208 byte |= 0x40; 209 if (d1 & 0x08) 210 byte |= 0x20; 211 if (d1 & 0x02) 212 byte |= 0x10; 213 if (d0 & 0x80) 214 byte |= 0x08; 215 if (d0 & 0x20) 216 byte |= 0x04; 217 if (d0 & 0x08) 218 byte |= 0x02; 219 if (d0 & 0x02) 220 byte |= 0x01; 221 222 if (d2 & 0x80) 223 bit |= 0x04; 224 if (d2 & 0x20) 225 bit |= 0x02; 226 if (d2 & 0x08) 227 bit |= 0x01; 228 229 data[byte] ^= (1 << bit); 230 231 return 1; /* Corrected the error */ 232 } 233 234 if ((yaffs_CountBits(d0) + 235 yaffs_CountBits(d1) + 236 yaffs_CountBits(d2)) == 1) { 237 /* Reccoverable error in ecc */ 238 239 read_ecc[0] = test_ecc[0]; 240 read_ecc[1] = test_ecc[1]; 241 read_ecc[2] = test_ecc[2]; 242 243 return 1; /* Corrected the error */ 244 } 245 246 /* Unrecoverable error */ 247 248 return -1; 249 250 } 251 252 253 /* 254 * ECCxxxOther does ECC calcs on arbitrary n bytes of data 255 */ 256 void yaffs_ECCCalculateOther(const unsigned char *data, unsigned nBytes, 257 yaffs_ECCOther * eccOther) 258 { 259 unsigned int i; 260 261 unsigned char col_parity = 0; 262 unsigned line_parity = 0; 263 unsigned line_parity_prime = 0; 264 unsigned char b; 265 266 for (i = 0; i < nBytes; i++) { 267 b = column_parity_table[*data++]; 268 col_parity ^= b; 269 270 if (b & 0x01) { 271 /* odd number of bits in the byte */ 272 line_parity ^= i; 273 line_parity_prime ^= ~i; 274 } 275 276 } 277 278 eccOther->colParity = (col_parity >> 2) & 0x3f; 279 eccOther->lineParity = line_parity; 280 eccOther->lineParityPrime = line_parity_prime; 281 } 282 283 int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes, 284 yaffs_ECCOther * read_ecc, 285 const yaffs_ECCOther * test_ecc) 286 { 287 unsigned char cDelta; /* column parity delta */ 288 unsigned lDelta; /* line parity delta */ 289 unsigned lDeltaPrime; /* line parity delta */ 290 unsigned bit; 291 292 cDelta = read_ecc->colParity ^ test_ecc->colParity; 293 lDelta = read_ecc->lineParity ^ test_ecc->lineParity; 294 lDeltaPrime = read_ecc->lineParityPrime ^ test_ecc->lineParityPrime; 295 296 if ((cDelta | lDelta | lDeltaPrime) == 0) 297 return 0; /* no error */ 298 299 if (lDelta == ~lDeltaPrime && 300 (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15)) 301 { 302 /* Single bit (recoverable) error in data */ 303 304 bit = 0; 305 306 if (cDelta & 0x20) 307 bit |= 0x04; 308 if (cDelta & 0x08) 309 bit |= 0x02; 310 if (cDelta & 0x02) 311 bit |= 0x01; 312 313 if(lDelta >= nBytes) 314 return -1; 315 316 data[lDelta] ^= (1 << bit); 317 318 return 1; /* corrected */ 319 } 320 321 if ((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) + 322 yaffs_CountBits(cDelta)) == 1) { 323 /* Reccoverable error in ecc */ 324 325 *read_ecc = *test_ecc; 326 return 1; /* corrected */ 327 } 328 329 /* Unrecoverable error */ 330 331 return -1; 332 333 } 334