[Nand Flash]软件ECC
/*
---------------------------------------------------------------
作 者:温子祺
联系方式:[email protected]
说 明:软件ECC
文件来源:Microsoft
---------------------------------------------------------------
*/
文件路径 C:\WINCE600\PLATFORM\Mini2440\src\common\nandflash\fmd\ECC.c
源码：
代码
#include
<
windows.h
>
UCHAR CountNumberOfOnes(UCHAR num)
{
UCHAR count
=
0
;
while
(num)
{
num
=
num
&
(num
-
1
);
count
++
;
}
return
count;
}
#define
DATA_BUFF_LEN 512
#define
ECC_BUFF_LEN 3
//
# of bytes in ECC
#define
NO_DATA_ERROR 0
#define
ECC_ERROR 1
#define
CORRECTABLE_ERROR 12
//
Half of the ECC bits are 1
/*
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Function: ECC_CorrectData()
Description: Corrects any errors (if possible) in the specified data.
Notes: This implemention uses 3 bytes of ECC info for every 512 bytes
of data. Furthermore, a only single-bit error can be corrected
for every 512 bytes of data.
This code is based on the ECC algorithm publicly available on
Samsung's FLASH media website.
Returns: Boolean indicating if the data was corrected.
-------------------------------------------------------------------------------
*/
BOOL ECC_CorrectData(LPBYTE pData, LPBYTE pExistingECC, LPBYTE pNewECC)
{
DWORD i, numOnes, byteLocation, bitLocation;
BYTE xorECC[ECC_BUFF_LEN];
//
----- 1. Check the parameters -----
if
((pData
==
NULL)
||
(pExistingECC
==
NULL)
||
(pNewECC
==
NULL))
{
return
FALSE;
}
//
----- 2. First, determine if this is a single-bit, correctable, error -----
//
NOTE: To answer this question, the two ECC values are XOR'd
//
together and the total # of 1 bits is counted, which
//
then tell us if we can correct the erroneous single-bit
//
transition in the data.
for
(i
=
0
; i
<
ECC_BUFF_LEN; i
++
)
{
xorECC[i]
=
pExistingECC[i]
^
pNewECC[i];
}
numOnes
=
0
;
for
(i
=
0
; i
<
ECC_BUFF_LEN; i
++
)
{
numOnes
+=
CountNumberOfOnes(xorECC[i]);
}
switch
(numOnes)
{
case
NO_DATA_ERROR:
//
Data doesn't contain an error
return
TRUE;
case
ECC_ERROR:
//
Existing ECC value has gone bad!
return
FALSE;
case
CORRECTABLE_ERROR:
//
Single-bit error
break
;
default
:
//
More than a single-bit error
return
FALSE;
}
//
----- 3. Compute the location of the single-bit error -----
byteLocation
=
( ((xorECC[
2
]
&
0x02
)
<<
7
)
|
((xorECC[
1
]
&
0x80
))
|
((xorECC[
1
]
&
0x20
)
<<
1
)
|
((xorECC[
1
]
&
0x08
)
<<
2
)
|
((xorECC[
1
]
&
0x02
)
<<
3
)
|
((xorECC[
0
]
&
0x80
)
>>
4
)
|
((xorECC[
0
]
&
0x20
)
>>
3
)
|
((xorECC[
0
]
&
0x08
)
>>
2
)
|
((xorECC[
0
]
&
0x02
)
>>
1
) );
bitLocation
=
(((xorECC[
2
]
&
0x80
)
>>
5
)
|
((xorECC[
2
]
&
0x20
)
>>
4
)
|
((xorECC[
2
]
&
0x08
)
>>
3
) );
//
----- 4. Correct the single-bit error (set the bit to its complementary value) -----
if
(pData[byteLocation]
&
(
0x01
<<
bitLocation))
{
pData[byteLocation]
&=
~
(
0x01
<<
bitLocation);
//
0->1 error, set bit to 0
}
else
{
pData[byteLocation]
|=
(
0x01
<<
bitLocation);
//
1->0 error, set bit to 1
}
return
TRUE;
}
代码分析：
1）
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