www.pudn.com > yaffs2.zip > yaffs_ecc.c
/*
* YAFFS: Yet another FFS. A NAND-flash specific file system.
*
* yaffs_ecc.c: ECC generation/correction algorithms.
*
* Copyright (C) 2002 Aleph One Ltd.
*
* Created by Charles Manning
*
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public License
* version 2.1 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.
*
*/
// 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.
const char *yaffs_ecc_c_version = "$Id: yaffs_ecc.c,v 1.1 2004/11/03 08:14:07 charles Exp $";
#include "yaffs_ecc.h"
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,
};
static int yaffs_CountBits(unsigned char x)
{
int r = 0;
while(x)
{
if(x & 1) r++;
x >>= 1;
}
return r;
}
static int yaffs_CountBits32(unsigned x)
{
int r = 0;
while(x)
{
if(x & 1) r++;
x >>= 1;
}
return r;
}
void yaffs_ECCCalculate(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;
#ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
// Swap the bytes into the wrong order
t = ecc[0];
ecc[0] = ecc[1];
ecc[1] = t;
#endif
}
int yaffs_ECCCorrect(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)
{
// no error
return 0;
}
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;
#ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
// swap the bytes to correct for the wrong order
unsigned char t;
t = d0;
d0 = d1;
d1 = t;
#endif
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;
}
if((yaffs_CountBits(d0)+yaffs_CountBits(d1)+yaffs_CountBits(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;
}
// Unrecoverable error
return -1;
}
void yaffs_ECCCalculateOther(const unsigned char *data,unsigned nBytes, yaffs_ECCOther *eccOther)
{
unsigned int i;
unsigned char col_parity = 0;
unsigned line_parity = 0;
unsigned line_parity_prime = 0;
unsigned char b;
for(i = 0; i < nBytes; 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;
}
}
eccOther->colParity = (col_parity >> 2) & 0x3f;
eccOther->lineParity = line_parity;
eccOther->lineParityPrime = line_parity_prime;
}
int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes, yaffs_ECCOther *read_ecc, const yaffs_ECCOther *test_ecc)
{
unsigned char cDelta; // column parity delta
unsigned lDelta; // line parity delta
unsigned lDeltaPrime; // line parity delta
unsigned bit;
cDelta = read_ecc->colParity ^ test_ecc->colParity;
lDelta = read_ecc->lineParity ^ test_ecc->lineParity;
lDeltaPrime = read_ecc->lineParityPrime ^ test_ecc->lineParityPrime;
if((cDelta | lDelta | lDeltaPrime) == 0)
{
// no error
return 0;
}
if( lDelta == ~lDeltaPrime &&
(((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15)) // Not correct
{
// Single bit (recoverable) error in data
#if 0
unsigned byte;
unsigned bit;
#endif
#ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
// swap the bytes to correct for the wrong order
unsigned char t;
t = d0;
d0 = d1;
d1 = t;
#endif
bit = 0;
if(cDelta & 0x20) bit |= 0x04;
if(cDelta & 0x08) bit |= 0x02;
if(cDelta & 0x02) bit |= 0x01;
data[lDelta] ^= (1 << bit);
return 1;
}
if((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) + yaffs_CountBits(cDelta)) == 1)
{
// Reccoverable error in ecc
*read_ecc = *test_ecc;
return 1;
}
// Unrecoverable error
return -1;
}