/*
* 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 <charles@aleph1.co.uk>
*
*
* 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 1.7 2006/09/14 22:02:46 charles Exp $";
#include "yportenv.h"
#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,
};
/* Count the bits in an unsigned char or a U32 */
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;
}
/* Calculate the ECC for a 256-byte block of data */
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
}
/* Correct the ECC on a 256 byte block of data */
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)
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;
#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; /* Corrected the error */
}
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; /* Corrected the error */
}
/* Unrecoverable error */
return -1;
}
/*
* ECCxxxOther does ECC calcs on arbitrary n bytes of data
*/
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)
return 0; /* no error */
if (lDelta == ~lDeltaPrime &&
(((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15))
{
/* Single bit (recoverable) error in data */
bit = 0;
if (cDelta & 0x20)
bit |= 0x04;
if (cDelta & 0x08)
bit |= 0x02;
if (cDelta & 0x02)
bit |= 0x01;
if(lDelta >= nBytes)
return -1;
data[lDelta] ^= (1 << bit);
return 1; /* corrected */
}
if ((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) +
yaffs_CountBits(cDelta)) == 1) {
/* Reccoverable error in ecc */
*read_ecc = *test_ecc;
return 1; /* corrected */
}
/* Unrecoverable error */
return -1;
}