-
Notifications
You must be signed in to change notification settings - Fork 0
/
yaffs_ecc.c
280 lines (232 loc) · 6.92 KB
/
yaffs_ecc.c
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
/*
* YAFFS: Yet Another Flash File System. A NAND-flash specific file system.
*
* Copyright (C) 2002-2018 Aleph One Ltd.
*
* Created by Charles Manning <charles@aleph1.co.uk>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
/*
* This code implements the ECC algorithm used in SmartMedia.
*
* The ECC comprises 22 bits of parity information and is stuffed into 3 bytes.
* The two unused bit are set to 1.
* The ECC can correct single bit errors in a 256-byte page of data. Thus, two
* such ECC blocks are used on a 512-byte NAND page.
*
*/
#include "yportenv.h"
#include "yaffs_ecc.h"
/* Table generated by gen-ecc.c
* Using a table means we do not have to calculate p1..p4 and p1'..p4'
* for each byte of data. These are instead provided in a table in bits7..2.
* Bit 0 of each entry indicates whether the entry has an odd or even parity,
* and therefore this bytes influence on the line parity.
*/
static const unsigned char column_parity_table[] = {
0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
};
/* Calculate the ECC for a 256-byte block of data */
void yaffs_ecc_calc(const unsigned char *data, unsigned char *ecc)
{
unsigned int i;
unsigned char col_parity = 0;
unsigned char line_parity = 0;
unsigned char line_parity_prime = 0;
unsigned char t;
unsigned char b;
for (i = 0; i < 256; i++) {
b = column_parity_table[*data++];
col_parity ^= b;
if (b & 0x01) { /* odd number of bits in the byte */
line_parity ^= i;
line_parity_prime ^= ~i;
}
}
ecc[2] = (~col_parity) | 0x03;
t = 0;
if (line_parity & 0x80)
t |= 0x80;
if (line_parity_prime & 0x80)
t |= 0x40;
if (line_parity & 0x40)
t |= 0x20;
if (line_parity_prime & 0x40)
t |= 0x10;
if (line_parity & 0x20)
t |= 0x08;
if (line_parity_prime & 0x20)
t |= 0x04;
if (line_parity & 0x10)
t |= 0x02;
if (line_parity_prime & 0x10)
t |= 0x01;
ecc[1] = ~t;
t = 0;
if (line_parity & 0x08)
t |= 0x80;
if (line_parity_prime & 0x08)
t |= 0x40;
if (line_parity & 0x04)
t |= 0x20;
if (line_parity_prime & 0x04)
t |= 0x10;
if (line_parity & 0x02)
t |= 0x08;
if (line_parity_prime & 0x02)
t |= 0x04;
if (line_parity & 0x01)
t |= 0x02;
if (line_parity_prime & 0x01)
t |= 0x01;
ecc[0] = ~t;
}
/* Correct the ECC on a 256 byte block of data */
int yaffs_ecc_correct(unsigned char *data, unsigned char *read_ecc,
const unsigned char *test_ecc)
{
unsigned char d0, d1, d2; /* deltas */
d0 = read_ecc[0] ^ test_ecc[0];
d1 = read_ecc[1] ^ test_ecc[1];
d2 = read_ecc[2] ^ test_ecc[2];
if ((d0 | d1 | d2) == 0)
return 0; /* no error */
if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 &&
((d1 ^ (d1 >> 1)) & 0x55) == 0x55 &&
((d2 ^ (d2 >> 1)) & 0x54) == 0x54) {
/* Single bit (recoverable) error in data */
unsigned byte;
unsigned bit;
bit = byte = 0;
if (d1 & 0x80)
byte |= 0x80;
if (d1 & 0x20)
byte |= 0x40;
if (d1 & 0x08)
byte |= 0x20;
if (d1 & 0x02)
byte |= 0x10;
if (d0 & 0x80)
byte |= 0x08;
if (d0 & 0x20)
byte |= 0x04;
if (d0 & 0x08)
byte |= 0x02;
if (d0 & 0x02)
byte |= 0x01;
if (d2 & 0x80)
bit |= 0x04;
if (d2 & 0x20)
bit |= 0x02;
if (d2 & 0x08)
bit |= 0x01;
data[byte] ^= (1 << bit);
return 1; /* Corrected the error */
}
if ((hweight8(d0) + hweight8(d1) + hweight8(d2)) == 1) {
/* Reccoverable error in ecc */
read_ecc[0] = test_ecc[0];
read_ecc[1] = test_ecc[1];
read_ecc[2] = test_ecc[2];
return 1; /* Corrected the error */
}
/* Unrecoverable error */
return -1;
}
/*
* ECCxxxOther does ECC calcs on arbitrary n bytes of data
*/
void yaffs_ecc_calc_other(const unsigned char *data, unsigned n_bytes,
struct yaffs_ecc_other *ecc_other)
{
unsigned int i;
unsigned char col_parity = 0;
unsigned line_parity = 0;
unsigned line_parity_prime = 0;
unsigned char b;
for (i = 0; i < n_bytes; i++) {
b = column_parity_table[*data++];
col_parity ^= b;
if (b & 0x01) {
/* odd number of bits in the byte */
line_parity ^= i;
line_parity_prime ^= ~i;
}
}
ecc_other->col_parity = (col_parity >> 2) & 0x3f;
ecc_other->line_parity = line_parity;
ecc_other->line_parity_prime = line_parity_prime;
}
int yaffs_ecc_correct_other(unsigned char *data, unsigned n_bytes,
struct yaffs_ecc_other *read_ecc,
const struct yaffs_ecc_other *test_ecc)
{
unsigned char delta_col; /* column parity delta */
unsigned delta_line; /* line parity delta */
unsigned delta_line_prime; /* line parity delta */
unsigned bit;
delta_col = read_ecc->col_parity ^ test_ecc->col_parity;
delta_line = read_ecc->line_parity ^ test_ecc->line_parity;
delta_line_prime =
read_ecc->line_parity_prime ^ test_ecc->line_parity_prime;
if ((delta_col | delta_line | delta_line_prime) == 0)
return 0; /* no error */
if (delta_line == ~delta_line_prime &&
(((delta_col ^ (delta_col >> 1)) & 0x15) == 0x15)) {
/* Single bit (recoverable) error in data */
bit = 0;
if (delta_col & 0x20)
bit |= 0x04;
if (delta_col & 0x08)
bit |= 0x02;
if (delta_col & 0x02)
bit |= 0x01;
if (delta_line >= n_bytes)
return -1;
data[delta_line] ^= (1 << bit);
return 1; /* corrected */
}
if ((hweight32(delta_line) +
hweight32(delta_line_prime) +
hweight8(delta_col)) == 1) {
/* Reccoverable error in ecc */
*read_ecc = *test_ecc;
return 1; /* corrected */
}
/* Unrecoverable error */
return -1;
}