2 * YAFFS: Yet Another Flash File System. A NAND-flash specific file system.
4 * Copyright (C) 2002-2010 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.
33 #include "yaffs_ecc.h"
35 static const unsigned char column_parity_table[] = {
36 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
37 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
38 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
39 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
40 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
41 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
42 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
43 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
44 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
45 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
46 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
47 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
48 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
49 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
50 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
51 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
52 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
53 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
54 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
55 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
56 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
57 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
58 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
59 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
60 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
61 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
62 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
63 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
64 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
65 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
66 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
67 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
70 /* Count the bits in an unsigned char or a U32 */
72 static int yaffs_count_bits(unsigned char x)
83 static int yaffs_count_bits32(unsigned x)
94 /* Calculate the ECC for a 256-byte block of data */
95 void yaffs_ecc_cacl(const unsigned char *data, unsigned char *ecc)
99 unsigned char col_parity = 0;
100 unsigned char line_parity = 0;
101 unsigned char line_parity_prime = 0;
105 for (i = 0; i < 256; i++) {
106 b = column_parity_table[*data++];
109 if (b & 0x01) { /* odd number of bits in the byte */
111 line_parity_prime ^= ~i;
115 ecc[2] = (~col_parity) | 0x03;
118 if (line_parity & 0x80)
120 if (line_parity_prime & 0x80)
122 if (line_parity & 0x40)
124 if (line_parity_prime & 0x40)
126 if (line_parity & 0x20)
128 if (line_parity_prime & 0x20)
130 if (line_parity & 0x10)
132 if (line_parity_prime & 0x10)
137 if (line_parity & 0x08)
139 if (line_parity_prime & 0x08)
141 if (line_parity & 0x04)
143 if (line_parity_prime & 0x04)
145 if (line_parity & 0x02)
147 if (line_parity_prime & 0x02)
149 if (line_parity & 0x01)
151 if (line_parity_prime & 0x01)
155 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
156 /* Swap the bytes into the wrong order */
163 /* Correct the ECC on a 256 byte block of data */
165 int yaffs_ecc_correct(unsigned char *data, unsigned char *read_ecc,
166 const unsigned char *test_ecc)
168 unsigned char d0, d1, d2; /* deltas */
170 d0 = read_ecc[0] ^ test_ecc[0];
171 d1 = read_ecc[1] ^ test_ecc[1];
172 d2 = read_ecc[2] ^ test_ecc[2];
174 if ((d0 | d1 | d2) == 0)
175 return 0; /* no error */
177 if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 &&
178 ((d1 ^ (d1 >> 1)) & 0x55) == 0x55 &&
179 ((d2 ^ (d2 >> 1)) & 0x54) == 0x54) {
180 /* Single bit (recoverable) error in data */
185 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
186 /* swap the bytes to correct for the wrong order */
220 data[byte] ^= (1 << bit);
222 return 1; /* Corrected the error */
225 if ((yaffs_count_bits(d0) +
226 yaffs_count_bits(d1) + yaffs_count_bits(d2)) == 1) {
227 /* Reccoverable error in ecc */
229 read_ecc[0] = test_ecc[0];
230 read_ecc[1] = test_ecc[1];
231 read_ecc[2] = test_ecc[2];
233 return 1; /* Corrected the error */
236 /* Unrecoverable error */
243 * ECCxxxOther does ECC calcs on arbitrary n bytes of data
245 void yaffs_ecc_calc_other(const unsigned char *data, unsigned n_bytes,
246 struct yaffs_ecc_other *ecc_other)
250 unsigned char col_parity = 0;
251 unsigned line_parity = 0;
252 unsigned line_parity_prime = 0;
255 for (i = 0; i < n_bytes; i++) {
256 b = column_parity_table[*data++];
260 /* odd number of bits in the byte */
262 line_parity_prime ^= ~i;
267 ecc_other->col_parity = (col_parity >> 2) & 0x3f;
268 ecc_other->line_parity = line_parity;
269 ecc_other->line_parity_prime = line_parity_prime;
272 int yaffs_ecc_correct_other(unsigned char *data, unsigned n_bytes,
273 struct yaffs_ecc_other *read_ecc,
274 const struct yaffs_ecc_other *test_ecc)
276 unsigned char delta_col; /* column parity delta */
277 unsigned delta_line; /* line parity delta */
278 unsigned delta_line_prime; /* line parity delta */
281 delta_col = read_ecc->col_parity ^ test_ecc->col_parity;
282 delta_line = read_ecc->line_parity ^ test_ecc->line_parity;
284 read_ecc->line_parity_prime ^ test_ecc->line_parity_prime;
286 if ((delta_col | delta_line | delta_line_prime) == 0)
287 return 0; /* no error */
289 if (delta_line == ~delta_line_prime &&
290 (((delta_col ^ (delta_col >> 1)) & 0x15) == 0x15)) {
291 /* Single bit (recoverable) error in data */
295 if (delta_col & 0x20)
297 if (delta_col & 0x08)
299 if (delta_col & 0x02)
302 if (delta_line >= n_bytes)
305 data[delta_line] ^= (1 << bit);
307 return 1; /* corrected */
310 if ((yaffs_count_bits32(delta_line) +
311 yaffs_count_bits32(delta_line_prime) +
312 yaffs_count_bits(delta_col)) == 1) {
313 /* Reccoverable error in ecc */
315 *read_ecc = *test_ecc;
316 return 1; /* corrected */
319 /* Unrecoverable error */