/* * 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 1.3 2004/04/04 03:47:02 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;}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;	    }