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Diffstat (limited to 'fs/yaffs2/yaffs_ecc.c')
| -rw-r--r-- | fs/yaffs2/yaffs_ecc.c | 333 |
1 files changed, 333 insertions, 0 deletions
diff --git a/fs/yaffs2/yaffs_ecc.c b/fs/yaffs2/yaffs_ecc.c new file mode 100644 index 0000000..a05a6b5 --- /dev/null +++ b/fs/yaffs2/yaffs_ecc.c @@ -0,0 +1,333 @@ +/* + * YAFFS: Yet Another Flash File System. A NAND-flash specific file system. + * + * Copyright (C) 2002-2007 Aleph One Ltd. + * for Toby Churchill Ltd and Brightstar Engineering + * + * 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 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. + * + */ + +/* 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. + */ + +/* XXX U-BOOT XXX */ +#include <common.h> + +const char *yaffs_ecc_c_version = + "$Id: yaffs_ecc.c,v 1.9 2007/02/14 01:09:06 wookey 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; + +} |