X-Git-Url: http://www.aleph1.co.uk/gitweb/?p=yaffs2.git;a=blobdiff_plain;f=yaffs_ecc.c;h=be860d01a6f3853695efb2a9184bb43ffe728927;hp=5cb49b416d90933513592aff8dfa8b6802bb9446;hb=a6c3366bdc908169673539dcb464369061ed5eb8;hpb=68f0159122cfb94e6912dd99d6398ba72e578a72 diff --git a/yaffs_ecc.c b/yaffs_ecc.c index 5cb49b4..be860d0 100644 --- a/yaffs_ecc.c +++ b/yaffs_ecc.c @@ -1,36 +1,35 @@ /* - * YAFFS: Yet another FFS. A NAND-flash specific file system. + * YAFFS: Yet Another Flash File System. A NAND-flash specific file system. * - * yaffs_ecc.c: ECC generation/correction algorithms. - * - * Copyright (C) 2002 Aleph One Ltd. + * Copyright (C) 2002-2007 Aleph One Ltd. + * for Toby Churchill Ltd and Brightstar Engineering * * Created by Charles Manning * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 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. * - * 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. +/* 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 1.5 2005-08-11 00:34:14 charles Exp $"; + "$Id: yaffs_ecc.c,v 1.9 2007-02-14 01:09:06 wookey Exp $"; #include "yportenv.h" @@ -71,6 +70,8 @@ static const unsigned char column_parity_table[] = { 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; @@ -93,6 +94,7 @@ static int yaffs_CountBits32(unsigned x) 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; @@ -163,24 +165,25 @@ void yaffs_ECCCalculate(const unsigned char *data, unsigned char *ecc) #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 + 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 | 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 + /* Single bit (recoverable) error in data */ unsigned byte; unsigned bit; @@ -222,25 +225,31 @@ int yaffs_ECCCorrect(unsigned char *data, unsigned char *read_ecc, data[byte] ^= (1 << bit); - return 1; + return 1; /* Corrected the error */ } - if ((yaffs_CountBits(d0) + yaffs_CountBits(d1) + yaffs_CountBits(d2)) == - 1) { - // Reccoverable error in ecc + 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; + return 1; /* Corrected the error */ } - // Unrecoverable 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) { @@ -255,8 +264,8 @@ void yaffs_ECCCalculateOther(const unsigned char *data, unsigned nBytes, b = column_parity_table[*data++]; col_parity ^= b; - if (b & 0x01) // odd number of bits in the byte - { + if (b & 0x01) { + /* odd number of bits in the byte */ line_parity ^= i; line_parity_prime ^= ~i; } @@ -272,23 +281,22 @@ 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 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 ((cDelta | lDelta | lDeltaPrime) == 0) + return 0; /* no error */ - if (lDelta == ~lDeltaPrime && (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15)) // Not correct + if (lDelta == ~lDeltaPrime && + (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15)) { - // Single bit (recoverable) error in data + /* Single bit (recoverable) error in data */ bit = 0; @@ -299,20 +307,25 @@ int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes, if (cDelta & 0x02) bit |= 0x01; + if(lDelta >= nBytes) + return -1; + data[lDelta] ^= (1 << bit); - return 1; + return 1; /* corrected */ } if ((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) + yaffs_CountBits(cDelta)) == 1) { - // Reccoverable error in ecc + /* Reccoverable error in ecc */ *read_ecc = *test_ecc; - return 1; + return 1; /* corrected */ } - // Unrecoverable error + + /* Unrecoverable error */ return -1; } +