2 * YAFFS: Yet Another Flash File System. A NAND-flash specific file system.
4 * Copyright (C) 2002-2007 Aleph One Ltd.
5 * for Toby Churchill Ltd and Brightstar Engineering
7 * Created by Charles Manning <charles@aleph1.co.uk>
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.
15 * This code implements the ECC algorithm used in SmartMedia.
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.
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.
31 const char *yaffs_ecc_c_version =
32 "$Id: yaffs_ecc.c,v 1.11 2009-03-06 17:20:50 wookey Exp $";
36 #include "yaffs_ecc.h"
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,
73 /* Count the bits in an unsigned char or a U32 */
75 static int yaffs_CountBits(unsigned char x)
86 static int yaffs_CountBits32(unsigned x)
97 /* Calculate the ECC for a 256-byte block of data */
98 void yaffs_ECCCalculate(const unsigned char *data, unsigned char *ecc)
102 unsigned char col_parity = 0;
103 unsigned char line_parity = 0;
104 unsigned char line_parity_prime = 0;
108 for (i = 0; i < 256; i++) {
109 b = column_parity_table[*data++];
112 if (b & 0x01) { /* odd number of bits in the byte */
114 line_parity_prime ^= ~i;
118 ecc[2] = (~col_parity) | 0x03;
121 if (line_parity & 0x80)
123 if (line_parity_prime & 0x80)
125 if (line_parity & 0x40)
127 if (line_parity_prime & 0x40)
129 if (line_parity & 0x20)
131 if (line_parity_prime & 0x20)
133 if (line_parity & 0x10)
135 if (line_parity_prime & 0x10)
140 if (line_parity & 0x08)
142 if (line_parity_prime & 0x08)
144 if (line_parity & 0x04)
146 if (line_parity_prime & 0x04)
148 if (line_parity & 0x02)
150 if (line_parity_prime & 0x02)
152 if (line_parity & 0x01)
154 if (line_parity_prime & 0x01)
158 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
159 /* Swap the bytes into the wrong order */
167 /* Correct the ECC on a 256 byte block of data */
169 int yaffs_ECCCorrect(unsigned char *data, unsigned char *read_ecc,
170 const unsigned char *test_ecc)
172 unsigned char d0, d1, d2; /* deltas */
174 d0 = read_ecc[0] ^ test_ecc[0];
175 d1 = read_ecc[1] ^ test_ecc[1];
176 d2 = read_ecc[2] ^ test_ecc[2];
178 if ((d0 | d1 | d2) == 0)
179 return 0; /* no error */
181 if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 &&
182 ((d1 ^ (d1 >> 1)) & 0x55) == 0x55 &&
183 ((d2 ^ (d2 >> 1)) & 0x54) == 0x54) {
184 /* Single bit (recoverable) error in data */
189 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
190 /* swap the bytes to correct for the wrong order */
224 data[byte] ^= (1 << bit);
226 return 1; /* Corrected the error */
229 if ((yaffs_CountBits(d0) +
230 yaffs_CountBits(d1) +
231 yaffs_CountBits(d2)) == 1) {
232 /* Reccoverable error in ecc */
234 read_ecc[0] = test_ecc[0];
235 read_ecc[1] = test_ecc[1];
236 read_ecc[2] = test_ecc[2];
238 return 1; /* Corrected the error */
241 /* Unrecoverable error */
249 * ECCxxxOther does ECC calcs on arbitrary n bytes of data
251 void yaffs_ECCCalculateOther(const unsigned char *data, unsigned nBytes,
252 yaffs_ECCOther *eccOther)
256 unsigned char col_parity = 0;
257 unsigned line_parity = 0;
258 unsigned line_parity_prime = 0;
261 for (i = 0; i < nBytes; i++) {
262 b = column_parity_table[*data++];
266 /* odd number of bits in the byte */
268 line_parity_prime ^= ~i;
273 eccOther->colParity = (col_parity >> 2) & 0x3f;
274 eccOther->lineParity = line_parity;
275 eccOther->lineParityPrime = line_parity_prime;
278 int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes,
279 yaffs_ECCOther *read_ecc,
280 const yaffs_ECCOther *test_ecc)
282 unsigned char cDelta; /* column parity delta */
283 unsigned lDelta; /* line parity delta */
284 unsigned lDeltaPrime; /* line parity delta */
287 cDelta = read_ecc->colParity ^ test_ecc->colParity;
288 lDelta = read_ecc->lineParity ^ test_ecc->lineParity;
289 lDeltaPrime = read_ecc->lineParityPrime ^ test_ecc->lineParityPrime;
291 if ((cDelta | lDelta | lDeltaPrime) == 0)
292 return 0; /* no error */
294 if (lDelta == ~lDeltaPrime &&
295 (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15)) {
296 /* Single bit (recoverable) error in data */
307 if (lDelta >= nBytes)
310 data[lDelta] ^= (1 << bit);
312 return 1; /* corrected */
315 if ((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) +
316 yaffs_CountBits(cDelta)) == 1) {
317 /* Reccoverable error in ecc */
319 *read_ecc = *test_ecc;
320 return 1; /* corrected */
323 /* Unrecoverable error */