/*
- * 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 <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.
*
- * 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 1.11 2009-03-06 17:20:50 wookey Exp $";
#include "yportenv.h"
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;
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;
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;
}
-
}
ecc[2] = (~col_parity) | 0x03;
ecc[0] = ~t;
#ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
- // Swap the bytes into the 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
+ 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;
#ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
- // swap the bytes to correct for the wrong order
+ /* swap the bytes to correct for the wrong order */
unsigned char t;
t = d0;
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)
+ yaffs_ECCOther *eccOther)
{
unsigned int i;
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;
}
}
int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes,
- yaffs_ECCOther * read_ecc,
- const yaffs_ECCOther * test_ecc)
+ 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
- {
- // Single bit (recoverable) error in data
+ if (lDelta == ~lDeltaPrime &&
+ (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15)) {
+ /* Single bit (recoverable) error in data */
bit = 0;
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
+ yaffs_CountBits(cDelta)) == 1) {
+ /* Reccoverable error in ecc */
*read_ecc = *test_ecc;
- return 1;
+ return 1; /* corrected */
}
- // Unrecoverable error
- return -1;
+ /* Unrecoverable error */
+ return -1;
}
projects / yaffs2.git / blobdiff