2 * YAFFS: Yet another FFS. A NAND-flash specific file system.
4 * yaffs_ecc.c: ECC generation/correction algorithms.
6 * Copyright (C) 2002 Aleph One Ltd.
8 * Created by Charles Manning <charles@aleph1.co.uk>
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.
17 * This code implements the ECC algorithm used in SmartMedia.
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.
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.
32 const char *yaffs_ecc_c_version =
33 "$Id: yaffs_ecc.c,v 1.5 2005-08-11 00:34:14 charles Exp $";
37 #include "yaffs_ecc.h"
39 static const unsigned char column_parity_table[] = {
40 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
41 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
42 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
43 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
44 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
45 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
46 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
47 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
48 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
49 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
50 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
51 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
52 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
53 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
54 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
55 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
56 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
57 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
58 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
59 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
60 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
61 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
62 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
63 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
64 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
65 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
66 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
67 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
68 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
69 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
70 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
71 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
74 static int yaffs_CountBits(unsigned char x)
85 static int yaffs_CountBits32(unsigned x)
96 void yaffs_ECCCalculate(const unsigned char *data, unsigned char *ecc)
100 unsigned char col_parity = 0;
101 unsigned char line_parity = 0;
102 unsigned char line_parity_prime = 0;
106 for (i = 0; i < 256; i++) {
107 b = column_parity_table[*data++];
110 if (b & 0x01) // odd number of bits in the byte
113 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
166 int yaffs_ECCCorrect(unsigned char *data, unsigned char *read_ecc,
167 const unsigned char *test_ecc)
169 unsigned char d0, d1, d2; // deltas
171 d0 = read_ecc[0] ^ test_ecc[0];
172 d1 = read_ecc[1] ^ test_ecc[1];
173 d2 = read_ecc[2] ^ test_ecc[2];
175 if ((d0 | d1 | d2) == 0) {
180 if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 &&
181 ((d1 ^ (d1 >> 1)) & 0x55) == 0x55 &&
182 ((d2 ^ (d2 >> 1)) & 0x54) == 0x54) {
183 // Single bit (recoverable) error in data
188 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
189 // swap the bytes to correct for the wrong order
223 data[byte] ^= (1 << bit);
228 if ((yaffs_CountBits(d0) + yaffs_CountBits(d1) + yaffs_CountBits(d2)) ==
230 // Reccoverable error in ecc
232 read_ecc[0] = test_ecc[0];
233 read_ecc[1] = test_ecc[1];
234 read_ecc[2] = test_ecc[2];
238 // Unrecoverable error
244 void yaffs_ECCCalculateOther(const unsigned char *data, unsigned nBytes,
245 yaffs_ECCOther * eccOther)
249 unsigned char col_parity = 0;
250 unsigned line_parity = 0;
251 unsigned line_parity_prime = 0;
254 for (i = 0; i < nBytes; i++) {
255 b = column_parity_table[*data++];
258 if (b & 0x01) // odd number of bits in the byte
261 line_parity_prime ^= ~i;
266 eccOther->colParity = (col_parity >> 2) & 0x3f;
267 eccOther->lineParity = line_parity;
268 eccOther->lineParityPrime = line_parity_prime;
271 int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes,
272 yaffs_ECCOther * read_ecc,
273 const yaffs_ECCOther * test_ecc)
275 unsigned char cDelta; // column parity delta
276 unsigned lDelta; // line parity delta
277 unsigned lDeltaPrime; // line parity delta
280 cDelta = read_ecc->colParity ^ test_ecc->colParity;
281 lDelta = read_ecc->lineParity ^ test_ecc->lineParity;
282 lDeltaPrime = read_ecc->lineParityPrime ^ test_ecc->lineParityPrime;
284 if ((cDelta | lDelta | lDeltaPrime) == 0) {
289 if (lDelta == ~lDeltaPrime && (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15)) // Not correct
291 // Single bit (recoverable) error in data
302 data[lDelta] ^= (1 << bit);
307 if ((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) +
308 yaffs_CountBits(cDelta)) == 1) {
309 // Reccoverable error in ecc
311 *read_ecc = *test_ecc;
314 // Unrecoverable error