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 1.9 2007-02-14 01:09:06 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
115 line_parity_prime ^= ~i;
120 ecc[2] = (~col_parity) | 0x03;
123 if (line_parity & 0x80)
125 if (line_parity_prime & 0x80)
127 if (line_parity & 0x40)
129 if (line_parity_prime & 0x40)
131 if (line_parity & 0x20)
133 if (line_parity_prime & 0x20)
135 if (line_parity & 0x10)
137 if (line_parity_prime & 0x10)
142 if (line_parity & 0x08)
144 if (line_parity_prime & 0x08)
146 if (line_parity & 0x04)
148 if (line_parity_prime & 0x04)
150 if (line_parity & 0x02)
152 if (line_parity_prime & 0x02)
154 if (line_parity & 0x01)
156 if (line_parity_prime & 0x01)
160 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
161 // Swap the bytes into the wrong order
169 /* Correct the ECC on a 256 byte block of data */
171 int yaffs_ECCCorrect(unsigned char *data, unsigned char *read_ecc,
172 const unsigned char *test_ecc)
174 unsigned char d0, d1, d2; /* deltas */
176 d0 = read_ecc[0] ^ test_ecc[0];
177 d1 = read_ecc[1] ^ test_ecc[1];
178 d2 = read_ecc[2] ^ test_ecc[2];
180 if ((d0 | d1 | d2) == 0)
181 return 0; /* no error */
183 if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 &&
184 ((d1 ^ (d1 >> 1)) & 0x55) == 0x55 &&
185 ((d2 ^ (d2 >> 1)) & 0x54) == 0x54) {
186 /* Single bit (recoverable) error in data */
191 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
192 // swap the bytes to correct for the wrong order
226 data[byte] ^= (1 << bit);
228 return 1; /* Corrected the error */
231 if ((yaffs_CountBits(d0) +
232 yaffs_CountBits(d1) +
233 yaffs_CountBits(d2)) == 1) {
234 /* Reccoverable error in ecc */
236 read_ecc[0] = test_ecc[0];
237 read_ecc[1] = test_ecc[1];
238 read_ecc[2] = test_ecc[2];
240 return 1; /* Corrected the error */
243 /* Unrecoverable error */
251 * ECCxxxOther does ECC calcs on arbitrary n bytes of data
253 void yaffs_ECCCalculateOther(const unsigned char *data, unsigned nBytes,
254 yaffs_ECCOther * eccOther)
258 unsigned char col_parity = 0;
259 unsigned line_parity = 0;
260 unsigned line_parity_prime = 0;
263 for (i = 0; i < nBytes; i++) {
264 b = column_parity_table[*data++];
268 /* odd number of bits in the byte */
270 line_parity_prime ^= ~i;
275 eccOther->colParity = (col_parity >> 2) & 0x3f;
276 eccOther->lineParity = line_parity;
277 eccOther->lineParityPrime = line_parity_prime;
280 int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes,
281 yaffs_ECCOther * read_ecc,
282 const yaffs_ECCOther * test_ecc)
284 unsigned char cDelta; /* column parity delta */
285 unsigned lDelta; /* line parity delta */
286 unsigned lDeltaPrime; /* line parity delta */
289 cDelta = read_ecc->colParity ^ test_ecc->colParity;
290 lDelta = read_ecc->lineParity ^ test_ecc->lineParity;
291 lDeltaPrime = read_ecc->lineParityPrime ^ test_ecc->lineParityPrime;
293 if ((cDelta | lDelta | lDeltaPrime) == 0)
294 return 0; /* no error */
296 if (lDelta == ~lDeltaPrime &&
297 (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15))
299 /* Single bit (recoverable) error in data */
313 data[lDelta] ^= (1 << bit);
315 return 1; /* corrected */
318 if ((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) +
319 yaffs_CountBits(cDelta)) == 1) {
320 /* Reccoverable error in ecc */
322 *read_ecc = *test_ecc;
323 return 1; /* corrected */
326 /* Unrecoverable error */