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282 lines
7.0 KiB
C
282 lines
7.0 KiB
C
/*
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* YAFFS: Yet Another Flash File System. A NAND-flash specific file system.
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*
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* Copyright (C) 2002-2011 Aleph One Ltd.
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* for Toby Churchill Ltd and Brightstar Engineering
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*
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* Created by Charles Manning <charles@aleph1.co.uk>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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/*
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* This code implements the ECC algorithm used in SmartMedia.
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*
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* The ECC comprises 22 bits of parity information and is stuffed into 3 bytes.
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* The two unused bit are set to 1.
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* The ECC can correct single bit errors in a 256-byte page of data. Thus, two
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* such ECC blocks are used on a 512-byte NAND page.
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*
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*/
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#include "yportenv.h"
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#include "yaffs_ecc.h"
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/* Table generated by gen-ecc.c
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* Using a table means we do not have to calculate p1..p4 and p1'..p4'
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* for each byte of data. These are instead provided in a table in bits7..2.
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* Bit 0 of each entry indicates whether the entry has an odd or even parity,
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* and therefore this bytes influence on the line parity.
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*/
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static const unsigned char column_parity_table[] = {
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0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
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0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
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0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
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0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
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0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
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0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
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0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
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0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
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0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
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0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
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0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
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0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
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0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
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0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
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0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
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0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
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0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
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0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
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0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
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0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
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0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
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0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
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0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
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0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
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0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
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0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
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0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
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0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
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0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
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0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
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0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
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0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
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};
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/* Calculate the ECC for a 256-byte block of data */
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void yaffs_ecc_calc(const unsigned char *data, unsigned char *ecc)
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{
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unsigned int i;
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unsigned char col_parity = 0;
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unsigned char line_parity = 0;
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unsigned char line_parity_prime = 0;
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unsigned char t;
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unsigned char b;
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for (i = 0; i < 256; i++) {
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b = column_parity_table[*data++];
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col_parity ^= b;
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if (b & 0x01) { /* odd number of bits in the byte */
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line_parity ^= i;
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line_parity_prime ^= ~i;
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}
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}
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ecc[2] = (~col_parity) | 0x03;
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t = 0;
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if (line_parity & 0x80)
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t |= 0x80;
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if (line_parity_prime & 0x80)
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t |= 0x40;
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if (line_parity & 0x40)
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t |= 0x20;
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if (line_parity_prime & 0x40)
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t |= 0x10;
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if (line_parity & 0x20)
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t |= 0x08;
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if (line_parity_prime & 0x20)
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t |= 0x04;
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if (line_parity & 0x10)
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t |= 0x02;
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if (line_parity_prime & 0x10)
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t |= 0x01;
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ecc[1] = ~t;
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t = 0;
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if (line_parity & 0x08)
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t |= 0x80;
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if (line_parity_prime & 0x08)
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t |= 0x40;
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if (line_parity & 0x04)
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t |= 0x20;
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if (line_parity_prime & 0x04)
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t |= 0x10;
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if (line_parity & 0x02)
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t |= 0x08;
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if (line_parity_prime & 0x02)
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t |= 0x04;
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if (line_parity & 0x01)
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t |= 0x02;
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if (line_parity_prime & 0x01)
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t |= 0x01;
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ecc[0] = ~t;
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}
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/* Correct the ECC on a 256 byte block of data */
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int yaffs_ecc_correct(unsigned char *data, unsigned char *read_ecc,
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const unsigned char *test_ecc)
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{
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unsigned char d0, d1, d2; /* deltas */
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d0 = read_ecc[0] ^ test_ecc[0];
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d1 = read_ecc[1] ^ test_ecc[1];
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d2 = read_ecc[2] ^ test_ecc[2];
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if ((d0 | d1 | d2) == 0)
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return 0; /* no error */
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if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 &&
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((d1 ^ (d1 >> 1)) & 0x55) == 0x55 &&
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((d2 ^ (d2 >> 1)) & 0x54) == 0x54) {
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/* Single bit (recoverable) error in data */
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unsigned byte;
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unsigned bit;
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bit = byte = 0;
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if (d1 & 0x80)
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byte |= 0x80;
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if (d1 & 0x20)
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byte |= 0x40;
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if (d1 & 0x08)
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byte |= 0x20;
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if (d1 & 0x02)
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byte |= 0x10;
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if (d0 & 0x80)
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byte |= 0x08;
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if (d0 & 0x20)
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byte |= 0x04;
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if (d0 & 0x08)
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byte |= 0x02;
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if (d0 & 0x02)
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byte |= 0x01;
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if (d2 & 0x80)
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bit |= 0x04;
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if (d2 & 0x20)
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bit |= 0x02;
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if (d2 & 0x08)
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bit |= 0x01;
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data[byte] ^= (1 << bit);
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return 1; /* Corrected the error */
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}
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if ((hweight8(d0) + hweight8(d1) + hweight8(d2)) == 1) {
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/* Reccoverable error in ecc */
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read_ecc[0] = test_ecc[0];
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read_ecc[1] = test_ecc[1];
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read_ecc[2] = test_ecc[2];
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return 1; /* Corrected the error */
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}
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/* Unrecoverable error */
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return -1;
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}
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/*
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* ECCxxxOther does ECC calcs on arbitrary n bytes of data
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*/
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void yaffs_ecc_calc_other(const unsigned char *data, unsigned n_bytes,
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struct yaffs_ecc_other *ecc_other)
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{
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unsigned int i;
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unsigned char col_parity = 0;
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unsigned line_parity = 0;
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unsigned line_parity_prime = 0;
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unsigned char b;
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for (i = 0; i < n_bytes; i++) {
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b = column_parity_table[*data++];
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col_parity ^= b;
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if (b & 0x01) {
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/* odd number of bits in the byte */
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line_parity ^= i;
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line_parity_prime ^= ~i;
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}
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}
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ecc_other->col_parity = (col_parity >> 2) & 0x3f;
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ecc_other->line_parity = line_parity;
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ecc_other->line_parity_prime = line_parity_prime;
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}
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int yaffs_ecc_correct_other(unsigned char *data, unsigned n_bytes,
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struct yaffs_ecc_other *read_ecc,
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const struct yaffs_ecc_other *test_ecc)
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{
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unsigned char delta_col; /* column parity delta */
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unsigned delta_line; /* line parity delta */
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unsigned delta_line_prime; /* line parity delta */
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unsigned bit;
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delta_col = read_ecc->col_parity ^ test_ecc->col_parity;
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delta_line = read_ecc->line_parity ^ test_ecc->line_parity;
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delta_line_prime =
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read_ecc->line_parity_prime ^ test_ecc->line_parity_prime;
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if ((delta_col | delta_line | delta_line_prime) == 0)
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return 0; /* no error */
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if (delta_line == ~delta_line_prime &&
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(((delta_col ^ (delta_col >> 1)) & 0x15) == 0x15)) {
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/* Single bit (recoverable) error in data */
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bit = 0;
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if (delta_col & 0x20)
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bit |= 0x04;
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if (delta_col & 0x08)
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bit |= 0x02;
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if (delta_col & 0x02)
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bit |= 0x01;
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if (delta_line >= n_bytes)
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return -1;
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data[delta_line] ^= (1 << bit);
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return 1; /* corrected */
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}
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if ((hweight32(delta_line) +
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hweight32(delta_line_prime) +
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hweight8(delta_col)) == 1) {
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/* Reccoverable error in ecc */
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*read_ecc = *test_ecc;
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return 1; /* corrected */
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}
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/* Unrecoverable error */
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return -1;
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}
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