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 =
35 #include "yaffs_ecc.h"
37 static const unsigned char column_parity_table[] = {
38 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
39 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
40 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
41 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
42 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
43 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
44 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
45 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
46 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
47 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
48 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
49 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
50 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
51 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
52 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
53 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
54 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
55 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
56 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
57 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
58 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
59 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
60 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
61 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
62 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
63 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
64 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
65 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
66 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
67 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
68 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
69 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
72 /* Count the bits in an unsigned char or a U32 */
74 static int yaffs_CountBits(unsigned char x)
85 static int yaffs_CountBits32(unsigned x)
96 /* Calculate the ECC for a 256-byte block of data */
97 void yaffs_ECCCalculate(const unsigned char *data, unsigned char *ecc)
101 unsigned char col_parity = 0;
102 unsigned char line_parity = 0;
103 unsigned char line_parity_prime = 0;
107 for (i = 0; i < 256; i++) {
108 b = column_parity_table[*data++];
111 if (b & 0x01) // odd number of bits in the byte
114 line_parity_prime ^= ~i;
119 ecc[2] = (~col_parity) | 0x03;
122 if (line_parity & 0x80)
124 if (line_parity_prime & 0x80)
126 if (line_parity & 0x40)
128 if (line_parity_prime & 0x40)
130 if (line_parity & 0x20)
132 if (line_parity_prime & 0x20)
134 if (line_parity & 0x10)
136 if (line_parity_prime & 0x10)
141 if (line_parity & 0x08)
143 if (line_parity_prime & 0x08)
145 if (line_parity & 0x04)
147 if (line_parity_prime & 0x04)
149 if (line_parity & 0x02)
151 if (line_parity_prime & 0x02)
153 if (line_parity & 0x01)
155 if (line_parity_prime & 0x01)
159 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
160 // Swap the bytes into the wrong order
168 /* Correct the ECC on a 256 byte block of data */
170 int yaffs_ECCCorrect(unsigned char *data, unsigned char *read_ecc,
171 const unsigned char *test_ecc)
173 unsigned char d0, d1, d2; /* deltas */
175 d0 = read_ecc[0] ^ test_ecc[0];
176 d1 = read_ecc[1] ^ test_ecc[1];
177 d2 = read_ecc[2] ^ test_ecc[2];
179 if ((d0 | d1 | d2) == 0)
180 return 0; /* no error */
182 if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 &&
183 ((d1 ^ (d1 >> 1)) & 0x55) == 0x55 &&
184 ((d2 ^ (d2 >> 1)) & 0x54) == 0x54) {
185 /* Single bit (recoverable) error in data */
190 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
191 // swap the bytes to correct for the wrong order
225 data[byte] ^= (1 << bit);
227 return 1; /* Corrected the error */
230 if ((yaffs_CountBits(d0) +
231 yaffs_CountBits(d1) +
232 yaffs_CountBits(d2)) == 1) {
233 /* Reccoverable error in ecc */
235 read_ecc[0] = test_ecc[0];
236 read_ecc[1] = test_ecc[1];
237 read_ecc[2] = test_ecc[2];
239 return 1; /* Corrected the error */
242 /* Unrecoverable error */
250 * ECCxxxOther does ECC calcs on arbitrary n bytes of data
252 void yaffs_ECCCalculateOther(const unsigned char *data, unsigned nBytes,
253 yaffs_ECCOther * eccOther)
257 unsigned char col_parity = 0;
258 unsigned line_parity = 0;
259 unsigned line_parity_prime = 0;
262 for (i = 0; i < nBytes; i++) {
263 b = column_parity_table[*data++];
267 /* odd number of bits in the byte */
269 line_parity_prime ^= ~i;
274 eccOther->colParity = (col_parity >> 2) & 0x3f;
275 eccOther->lineParity = line_parity;
276 eccOther->lineParityPrime = line_parity_prime;
279 int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes,
280 yaffs_ECCOther * read_ecc,
281 const yaffs_ECCOther * test_ecc)
283 unsigned char cDelta; /* column parity delta */
284 unsigned lDelta; /* line parity delta */
285 unsigned lDeltaPrime; /* line parity delta */
288 cDelta = read_ecc->colParity ^ test_ecc->colParity;
289 lDelta = read_ecc->lineParity ^ test_ecc->lineParity;
290 lDeltaPrime = read_ecc->lineParityPrime ^ test_ecc->lineParityPrime;
292 if ((cDelta | lDelta | lDeltaPrime) == 0)
293 return 0; /* no error */
295 if (lDelta == ~lDeltaPrime &&
296 (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15))
298 /* Single bit (recoverable) error in data */
312 data[lDelta] ^= (1 << bit);
314 return 1; /* corrected */
317 if ((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) +
318 yaffs_CountBits(cDelta)) == 1) {
319 /* Reccoverable error in ecc */
321 *read_ecc = *test_ecc;
322 return 1; /* corrected */
325 /* Unrecoverable error */