2 * YAFFS: Yet another FFS. A NAND-flash specific file system.
4 * yaffs_ecc.c: ECC generation/correction algorithms.
6 * Copyright (C) 2002 Aleph One Ltd.
8 * Created by Charles Manning <charles@aleph1.co.uk>
11 * This program is free software; you can redistribute it and/or
12 * modify it under the terms of the GNU Lesser General Public License
13 * version 2.1 as published by the Free Software Foundation.
17 * This code implements the ECC algorithm used in SmartMedia.
19 * The ECC comprises 22 bits of parity information and is stuffed into 3 bytes.
20 * The two unused bit are set to 1.
21 * The ECC can correct single bit errors in a 256-byte page of data. Thus, two such ECC
22 * blocks are used on a 512-byte NAND page.
26 // Table generated by gen-ecc.c
27 // Using a table means we do not have to calculate p1..p4 and p1'..p4'
28 // for each byte of data. These are instead provided in a table in bits7..2.
29 // Bit 0 of each entry indicates whether the entry has an odd or even parity, and therefore
30 // this bytes influence on the line parity.
32 const char *yaffs_ecc_c_version = "$Id: yaffs_ecc.c,v 1.4 2005-07-31 00:28:04 charles Exp $";
36 #include "yaffs_ecc.h"
38 static const unsigned char column_parity_table[] = {
39 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69, 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
40 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc, 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
41 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0, 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
42 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65, 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
43 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc, 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
44 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59, 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
45 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55, 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
46 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0, 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
47 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0, 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
48 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55, 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
49 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59, 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
50 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc, 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
51 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65, 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
52 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0, 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
53 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc, 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
54 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69, 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
58 static int yaffs_CountBits(unsigned char x)
69 static int yaffs_CountBits32(unsigned x)
81 void yaffs_ECCCalculate(const unsigned char *data,unsigned char *ecc)
85 unsigned char col_parity = 0;
86 unsigned char line_parity = 0;
87 unsigned char line_parity_prime = 0;
91 for(i = 0; i < 256; i++)
93 b = column_parity_table[*data++];
96 if(b & 0x01) // odd number of bits in the byte
99 line_parity_prime ^= ~i;
104 ecc[2] = (~col_parity) | 0x03;
107 if(line_parity & 0x80) t |= 0x80;
108 if(line_parity_prime & 0x80) t |= 0x40;
109 if(line_parity & 0x40) t |= 0x20;
110 if(line_parity_prime & 0x40) t |= 0x10;
111 if(line_parity & 0x20) t |= 0x08;
112 if(line_parity_prime & 0x20) t |= 0x04;
113 if(line_parity & 0x10) t |= 0x02;
114 if(line_parity_prime & 0x10) t |= 0x01;
118 if(line_parity & 0x08) t |= 0x80;
119 if(line_parity_prime & 0x08) t |= 0x40;
120 if(line_parity & 0x04) t |= 0x20;
121 if(line_parity_prime & 0x04) t |= 0x10;
122 if(line_parity & 0x02) t |= 0x08;
123 if(line_parity_prime & 0x02) t |= 0x04;
124 if(line_parity & 0x01) t |= 0x02;
125 if(line_parity_prime & 0x01) t |= 0x01;
128 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
129 // Swap the bytes into the wrong order
136 int yaffs_ECCCorrect(unsigned char *data, unsigned char *read_ecc, const unsigned char *test_ecc)
138 unsigned char d0, d1, d2; // deltas
140 d0 = read_ecc[0] ^ test_ecc[0];
141 d1 = read_ecc[1] ^ test_ecc[1];
142 d2 = read_ecc[2] ^ test_ecc[2];
146 if((d0 | d1 | d2) == 0)
152 if( ((d0 ^ (d0 >> 1)) & 0x55) == 0x55 &&
153 ((d1 ^ (d1 >> 1)) & 0x55) == 0x55 &&
154 ((d2 ^ (d2 >> 1)) & 0x54) == 0x54)
156 // Single bit (recoverable) error in data
161 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
162 // swap the bytes to correct for the wrong order
173 if(d1 & 0x80) byte |= 0x80;
174 if(d1 & 0x20) byte |= 0x40;
175 if(d1 & 0x08) byte |= 0x20;
176 if(d1 & 0x02) byte |= 0x10;
177 if(d0 & 0x80) byte |= 0x08;
178 if(d0 & 0x20) byte |= 0x04;
179 if(d0 & 0x08) byte |= 0x02;
180 if(d0 & 0x02) byte |= 0x01;
182 if(d2 & 0x80) bit |= 0x04;
183 if(d2 & 0x20) bit |= 0x02;
184 if(d2 & 0x08) bit |= 0x01;
186 data[byte] ^= (1 << bit);
191 if((yaffs_CountBits(d0)+yaffs_CountBits(d1)+yaffs_CountBits(d2)) == 1)
193 // Reccoverable error in ecc
195 read_ecc[0] = test_ecc[0];
196 read_ecc[1] = test_ecc[1];
197 read_ecc[2] = test_ecc[2];
202 // Unrecoverable error
211 void yaffs_ECCCalculateOther(const unsigned char *data,unsigned nBytes, yaffs_ECCOther *eccOther)
215 unsigned char col_parity = 0;
216 unsigned line_parity = 0;
217 unsigned line_parity_prime = 0;
220 for(i = 0; i < nBytes; i++)
222 b = column_parity_table[*data++];
225 if(b & 0x01) // odd number of bits in the byte
228 line_parity_prime ^= ~i;
233 eccOther->colParity = (col_parity >> 2) & 0x3f;
234 eccOther->lineParity = line_parity;
235 eccOther->lineParityPrime = line_parity_prime;
238 int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes, yaffs_ECCOther *read_ecc, const yaffs_ECCOther *test_ecc)
240 unsigned char cDelta; // column parity delta
241 unsigned lDelta; // line parity delta
242 unsigned lDeltaPrime; // line parity delta
245 cDelta = read_ecc->colParity ^ test_ecc->colParity;
246 lDelta = read_ecc->lineParity ^ test_ecc->lineParity;
247 lDeltaPrime = read_ecc->lineParityPrime ^ test_ecc->lineParityPrime;
249 if((cDelta | lDelta | lDeltaPrime) == 0)
255 if( lDelta == ~lDeltaPrime &&
256 (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15)) // Not correct
258 // Single bit (recoverable) error in data
262 if(cDelta & 0x20) bit |= 0x04;
263 if(cDelta & 0x08) bit |= 0x02;
264 if(cDelta & 0x02) bit |= 0x01;
266 data[lDelta] ^= (1 << bit);
271 if((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) + yaffs_CountBits(cDelta)) == 1)
273 // Reccoverable error in ecc
275 *read_ecc = *test_ecc;
279 // Unrecoverable error