1 /*
2 * YAFFS: Yet Another Flash File System. A NAND-flash specific file system.
3 *
4 * Copyright (C) 2002-2007 Aleph One Ltd.
5 * for Toby Churchill Ltd and Brightstar Engineering
6 *
7 * Created by Charles Manning <charles@aleph1.co.uk>
8 *
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.
12 */
13
14 /*
15 * This code implements the ECC algorithm used in SmartMedia.
16 *
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.
21 *
22 */
23
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.
29 */
30
31 /* XXX U-BOOT XXX */
32 #include <common.h>
33
34 const char *yaffs_ecc_c_version =
35 "$Id: yaffs_ecc.c,v 1.9 2007/02/14 01:09:06 wookey Exp $";
36
37 #include "yportenv.h"
38
39 #include "yaffs_ecc.h"
40
41 static const unsigned char column_parity_table[] = {
42 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
43 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
44 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
45 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
46 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
47 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
48 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
49 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
50 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
51 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
52 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
53 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
54 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
55 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
56 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
57 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
58 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
59 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
60 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
61 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
62 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
63 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
64 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
65 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
66 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
67 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
68 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
69 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
70 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
71 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
72 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
73 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
74 };
75
76 /* Count the bits in an unsigned char or a U32 */
77
yaffs_CountBits(unsigned char x)78 static int yaffs_CountBits(unsigned char x)
79 {
80 int r = 0;
81 while (x) {
82 if (x & 1)
83 r++;
84 x >>= 1;
85 }
86 return r;
87 }
88
yaffs_CountBits32(unsigned x)89 static int yaffs_CountBits32(unsigned x)
90 {
91 int r = 0;
92 while (x) {
93 if (x & 1)
94 r++;
95 x >>= 1;
96 }
97 return r;
98 }
99
100 /* Calculate the ECC for a 256-byte block of data */
yaffs_ECCCalculate(const unsigned char * data,unsigned char * ecc)101 void yaffs_ECCCalculate(const unsigned char *data, unsigned char *ecc)
102 {
103 unsigned int i;
104
105 unsigned char col_parity = 0;
106 unsigned char line_parity = 0;
107 unsigned char line_parity_prime = 0;
108 unsigned char t;
109 unsigned char b;
110
111 for (i = 0; i < 256; i++) {
112 b = column_parity_table[*data++];
113 col_parity ^= b;
114
115 if (b & 0x01) // odd number of bits in the byte
116 {
117 line_parity ^= i;
118 line_parity_prime ^= ~i;
119 }
120
121 }
122
123 ecc[2] = (~col_parity) | 0x03;
124
125 t = 0;
126 if (line_parity & 0x80)
127 t |= 0x80;
128 if (line_parity_prime & 0x80)
129 t |= 0x40;
130 if (line_parity & 0x40)
131 t |= 0x20;
132 if (line_parity_prime & 0x40)
133 t |= 0x10;
134 if (line_parity & 0x20)
135 t |= 0x08;
136 if (line_parity_prime & 0x20)
137 t |= 0x04;
138 if (line_parity & 0x10)
139 t |= 0x02;
140 if (line_parity_prime & 0x10)
141 t |= 0x01;
142 ecc[1] = ~t;
143
144 t = 0;
145 if (line_parity & 0x08)
146 t |= 0x80;
147 if (line_parity_prime & 0x08)
148 t |= 0x40;
149 if (line_parity & 0x04)
150 t |= 0x20;
151 if (line_parity_prime & 0x04)
152 t |= 0x10;
153 if (line_parity & 0x02)
154 t |= 0x08;
155 if (line_parity_prime & 0x02)
156 t |= 0x04;
157 if (line_parity & 0x01)
158 t |= 0x02;
159 if (line_parity_prime & 0x01)
160 t |= 0x01;
161 ecc[0] = ~t;
162
163 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
164 // Swap the bytes into the wrong order
165 t = ecc[0];
166 ecc[0] = ecc[1];
167 ecc[1] = t;
168 #endif
169 }
170
171
172 /* Correct the ECC on a 256 byte block of data */
173
yaffs_ECCCorrect(unsigned char * data,unsigned char * read_ecc,const unsigned char * test_ecc)174 int yaffs_ECCCorrect(unsigned char *data, unsigned char *read_ecc,
175 const unsigned char *test_ecc)
176 {
177 unsigned char d0, d1, d2; /* deltas */
178
179 d0 = read_ecc[0] ^ test_ecc[0];
180 d1 = read_ecc[1] ^ test_ecc[1];
181 d2 = read_ecc[2] ^ test_ecc[2];
182
183 if ((d0 | d1 | d2) == 0)
184 return 0; /* no error */
185
186 if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 &&
187 ((d1 ^ (d1 >> 1)) & 0x55) == 0x55 &&
188 ((d2 ^ (d2 >> 1)) & 0x54) == 0x54) {
189 /* Single bit (recoverable) error in data */
190
191 unsigned byte;
192 unsigned bit;
193
194 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
195 // swap the bytes to correct for the wrong order
196 unsigned char t;
197
198 t = d0;
199 d0 = d1;
200 d1 = t;
201 #endif
202
203 bit = byte = 0;
204
205 if (d1 & 0x80)
206 byte |= 0x80;
207 if (d1 & 0x20)
208 byte |= 0x40;
209 if (d1 & 0x08)
210 byte |= 0x20;
211 if (d1 & 0x02)
212 byte |= 0x10;
213 if (d0 & 0x80)
214 byte |= 0x08;
215 if (d0 & 0x20)
216 byte |= 0x04;
217 if (d0 & 0x08)
218 byte |= 0x02;
219 if (d0 & 0x02)
220 byte |= 0x01;
221
222 if (d2 & 0x80)
223 bit |= 0x04;
224 if (d2 & 0x20)
225 bit |= 0x02;
226 if (d2 & 0x08)
227 bit |= 0x01;
228
229 data[byte] ^= (1 << bit);
230
231 return 1; /* Corrected the error */
232 }
233
234 if ((yaffs_CountBits(d0) +
235 yaffs_CountBits(d1) +
236 yaffs_CountBits(d2)) == 1) {
237 /* Reccoverable error in ecc */
238
239 read_ecc[0] = test_ecc[0];
240 read_ecc[1] = test_ecc[1];
241 read_ecc[2] = test_ecc[2];
242
243 return 1; /* Corrected the error */
244 }
245
246 /* Unrecoverable error */
247
248 return -1;
249
250 }
251
252
253 /*
254 * ECCxxxOther does ECC calcs on arbitrary n bytes of data
255 */
yaffs_ECCCalculateOther(const unsigned char * data,unsigned nBytes,yaffs_ECCOther * eccOther)256 void yaffs_ECCCalculateOther(const unsigned char *data, unsigned nBytes,
257 yaffs_ECCOther * eccOther)
258 {
259 unsigned int i;
260
261 unsigned char col_parity = 0;
262 unsigned line_parity = 0;
263 unsigned line_parity_prime = 0;
264 unsigned char b;
265
266 for (i = 0; i < nBytes; i++) {
267 b = column_parity_table[*data++];
268 col_parity ^= b;
269
270 if (b & 0x01) {
271 /* odd number of bits in the byte */
272 line_parity ^= i;
273 line_parity_prime ^= ~i;
274 }
275
276 }
277
278 eccOther->colParity = (col_parity >> 2) & 0x3f;
279 eccOther->lineParity = line_parity;
280 eccOther->lineParityPrime = line_parity_prime;
281 }
282
yaffs_ECCCorrectOther(unsigned char * data,unsigned nBytes,yaffs_ECCOther * read_ecc,const yaffs_ECCOther * test_ecc)283 int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes,
284 yaffs_ECCOther * read_ecc,
285 const yaffs_ECCOther * test_ecc)
286 {
287 unsigned char cDelta; /* column parity delta */
288 unsigned lDelta; /* line parity delta */
289 unsigned lDeltaPrime; /* line parity delta */
290 unsigned bit;
291
292 cDelta = read_ecc->colParity ^ test_ecc->colParity;
293 lDelta = read_ecc->lineParity ^ test_ecc->lineParity;
294 lDeltaPrime = read_ecc->lineParityPrime ^ test_ecc->lineParityPrime;
295
296 if ((cDelta | lDelta | lDeltaPrime) == 0)
297 return 0; /* no error */
298
299 if (lDelta == ~lDeltaPrime &&
300 (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15))
301 {
302 /* Single bit (recoverable) error in data */
303
304 bit = 0;
305
306 if (cDelta & 0x20)
307 bit |= 0x04;
308 if (cDelta & 0x08)
309 bit |= 0x02;
310 if (cDelta & 0x02)
311 bit |= 0x01;
312
313 if(lDelta >= nBytes)
314 return -1;
315
316 data[lDelta] ^= (1 << bit);
317
318 return 1; /* corrected */
319 }
320
321 if ((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) +
322 yaffs_CountBits(cDelta)) == 1) {
323 /* Reccoverable error in ecc */
324
325 *read_ecc = *test_ecc;
326 return 1; /* corrected */
327 }
328
329 /* Unrecoverable error */
330
331 return -1;
332
333 }
334