/****************************************************************************
* drivers/mtd/hamming.c
*
* Copyright (c) 2011, Atmel Corporation
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the names NuttX nor Atmel nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <assert.h>
#include <debug.h>
#include <nuttx/mtd/hamming.h>
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Name: hamming_bitsinbyte
*
* Description:
* Counts the number of bits set to '1' in the given byte.
*
* Input Parameters:
* bytes - The byte to use.
*
* Returned Value:
* Returns the number of bits set to '1' in the given byte.
*
****************************************************************************/
static unsigned int hamming_bitsinbyte(uint8_t byte)
{
unsigned int count = 0;
while (byte != 0)
{
if ((byte & 1) != 0)
{
count++;
}
byte >>= 1;
}
return count;
}
/****************************************************************************
* Name: hamming_bitsincode256
*
* Description:
* Counts the number of bits set to '1' in the given hamming code.
*
* Input Parameters:
* code - Hamming code
*
* Returned Value:
* Returns the number of bits set to '1' in the given hamming code.
*
****************************************************************************/
static uint8_t hamming_bitsincode256(FAR uint8_t *code)
{
return hamming_bitsinbyte(code[0]) +
hamming_bitsinbyte(code[1]) +
hamming_bitsinbyte(code[2]);
}
/****************************************************************************
* Name: hamming_compute256
*
* Description:
* Calculates the 22-bit hamming code for a 256-bytes block of data.
*
* Input Parameters:
* data - Data buffer to calculate code
* code - Pointer to a buffer where the code should be stored
*
* Returned Value:
* None
*
****************************************************************************/
static void hamming_compute256(FAR const uint8_t *data, FAR uint8_t *code)
{
uint8_t colsum = 0;
uint8_t evenline = 0;
uint8_t oddline = 0;
uint8_t evencol = 0;
uint8_t oddcol = 0;
int i;
/* Xor all bytes together to get the column sum;
* At the same time, calculate the even and odd line codes
*/
for (i = 0; i < 256; i++)
{
colsum ^= data[i];
/* If the xor sum of the byte is 0, then this byte has no incidence on
* the computed code; so check if the sum is 1.
*/
if ((hamming_bitsinbyte(data[i]) & 1) == 1)
{
/* Parity groups are formed by forcing a particular index bit to 0
* (even) or 1 (odd).
* Example on one byte:
*
* bits (dec) 7 6 5 4 3 2 1 0
* (bin) 111 110 101 100 011 010 001 000
* '---'---'---'----------.
* |
* groups P4' ooooooooooooooo eeeeeeeeeeeeeee P4 |
* P2' ooooooo eeeeeee ooooooo eeeeeee P2 |
* P1' ooo eee ooo eee ooo eee ooo eee P1 |
* |
* We can see that: |
* - P4 -> bit 2 of index is 0 --------------------'
* - P4' -> bit 2 of index is 1.
* - P2 -> bit 1 of index if 0.
* - etc...
* We deduce that a bit position has an impact on all even Px if
* the log2(x)nth bit of its index is 0
* ex: log2(4) = 2, bit2 of the index must be 0 (-> 0 1 2 3)
* and on all odd Px' if the log2(x)nth bit of its index is 1
* ex: log2(2) = 1, bit1 of the index must be 1 (-> 0 1 4 5)
*
* As such, we calculate all the possible Px and Px' values at the
* same time in two variables, evenline and oddline, such as
* evenline bits: P128 P64 P32 P16 P8 P4 P2 P1
* oddline bits: P128' P64' P32' P16' P8' P4' P2' P1'
*/
evenline ^= (255 - i);
oddline ^= i;
}
}
/* At this point, we have the line parities, and the column sum. First, We
* must calculate the parity group values on the column sum.
*/
for (i = 0; i < 8; i++)
{
if (colsum & 1)
{
evencol ^= (7 - i);
oddcol ^= i;
}
colsum >>= 1;
}
/* Now, we must interleave the parity values,
* to obtain the following layout:
* Code[0] = Line1
* Code[1] = Line2
* Code[2] = Column
* Line = Px' Px P(x-1)- P(x-1) ...
* Column = P4' P4 P2' P2 P1' P1 PadBit PadBit
*/
code[0] = 0;
code[1] = 0;
code[2] = 0;
for (i = 0; i < 4; i++)
{
code[0] <<= 2;
code[1] <<= 2;
code[2] <<= 2;
/* Line 1 */
if ((oddline & 0x80) != 0)
{
code[0] |= 2;
}
if ((evenline & 0x80) != 0)
{
code[0] |= 1;
}
/* Line 2 */
if ((oddline & 0x08) != 0)
{
code[1] |= 2;
}
if ((evenline & 0x08) != 0)
{
code[1] |= 1;
}
/* Column */
if ((oddcol & 0x04) != 0)
{
code[2] |= 2;
}
if ((evencol & 0x04) != 0)
{
code[2] |= 1;
}
oddline <<= 1;
evenline <<= 1;
oddcol <<= 1;
evencol <<= 1;
}
/* Invert codes (linux compatibility) */
code[0] = (~(uint32_t)code[0]);
code[1] = (~(uint32_t)code[1]);
code[2] = (~(uint32_t)code[2]);
}
/****************************************************************************
* Name: hamming_verify256
*
* Description:
* Verifies and corrects a 256-bytes block of data using the given 22-bits
* hamming code.
*
* Input Parameters:
* data - Data buffer to check
* original - Hamming code to use for verifying the data
*
* Returned Value:
* Zero on success, otherwise returns a HAMMING_ERROR_ code.
*
****************************************************************************/
static int hamming_verify256(FAR uint8_t *data, FAR const uint8_t *original)
{
/* Calculate new code */
uint8_t computed[3];
uint8_t correction[3];
hamming_compute256(data, computed);
/* Xor both codes together */
correction[0] = computed[0] ^ original[0];
correction[1] = computed[1] ^ original[1];
correction[2] = computed[2] ^ original[2];
/* If all bytes are 0, there is no error */
if ((correction[0] == 0) && (correction[1] == 0) && (correction[2] == 0))
{
return 0;
}
/* There are bit errors */
finfo("Read: %02x %02x %02x\n",
original[0], original[1], original[2]);
finfo("Computed: %02x %02x %02x\n",
computed[0], computed[1], computed[2]);
finfo("Correction: %02x %02x %02x\n",
correction[0], correction[1], correction[2]);
/* If there is a single bit error, there are 11 bits set to 1 */
if (hamming_bitsincode256(correction) == 11)
{
uint8_t byte;
uint8_t bit;
/* Get byte and bit indexes */
byte = correction[0] & 0x80;
byte |= (correction[0] << 1) & 0x40;
byte |= (correction[0] << 2) & 0x20;
byte |= (correction[0] << 3) & 0x10;
byte |= (correction[1] >> 4) & 0x08;
byte |= (correction[1] >> 3) & 0x04;
byte |= (correction[1] >> 2) & 0x02;
byte |= (correction[1] >> 1) & 0x01;
bit = (correction[2] >> 5) & 0x04;
bit |= (correction[2] >> 4) & 0x02;
bit |= (correction[2] >> 3) & 0x01;
/* Correct bit */
finfo("Correcting byte %d at bit %d\n", byte, bit);
data[byte] ^= (1 << bit);
return HAMMING_ERROR_SINGLEBIT;
}
/* Check if ECC has been corrupted */
if (hamming_bitsincode256(correction) == 1)
{
ferr("ERROR: ECC has been correupted\n");
return HAMMING_ERROR_ECC;
}
/* Otherwise, there are multiple bit errors */
else
{
ferr("ERROR: Multiple bit errors\n");
return HAMMING_ERROR_MULTIPLEBITS;
}
}
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: hamming_compute256x
*
* Description:
* Computes 3-bytes hamming codes for a data block whose size is multiple
* of 256 bytes. Each 256 bytes block gets its own code.
*
* Input Parameters:
* data - Data to compute code for
* size - Data size in bytes
* code - Codes buffer
*
* Returned Value:
* None
*
****************************************************************************/
void hamming_compute256x(FAR const uint8_t *data, size_t size,
FAR uint8_t *code)
{
ssize_t remaining = (ssize_t)size;
DEBUGASSERT((size & 0xff) == 0);
/* Loop, computing the Hamming code on each 256 byte chunk of data */
while (remaining > 0)
{
hamming_compute256(data, code);
/* Setup for the next 256 byte chunk */
data += 256;
code += 3;
remaining -= 256;
}
}
/****************************************************************************
* Name: hamming_verify256x
*
* Description:
* Verifies 3-bytes hamming codes for a data block whose size is multiple
* of 256 bytes. Each 256-bytes block is verified with its own code.
*
* Input Parameters:
* data - Data buffer to verify
* size - Size of the data in bytes
* code - Original codes
*
* Returned Value:
* Return 0 if the data is correct, HAMMING_ERROR_SINGLEBIT if one or more
* block(s) have had a single bit corrected, or either HAMMING_ERROR_ECC
* or HAMMING_ERROR_MULTIPLEBITS.
*
****************************************************************************/
int hamming_verify256x(FAR uint8_t *data,
size_t size,
FAR const uint8_t *code)
{
ssize_t remaining = (ssize_t)size;
int result = HAMMING_SUCCESS;
int ret;
DEBUGASSERT((size & 0xff) == 0);
/* Loop, verifying each 256 byte chunk of data */
while (remaining > 0)
{
result = hamming_verify256(data, code);
if (result != HAMMING_SUCCESS)
{
/* Check for the case of a single bit error that was corrected */
if (result == HAMMING_ERROR_SINGLEBIT)
{
/* Report the error, but continue verifying */
ret = HAMMING_ERROR_SINGLEBIT;
}
else
{
/* A bad error occurred, abort the verification and return the
* error code
*/
return result;
}
}
/* Setup for the next 256 byte chunk */
data += 256;
code += 3;
remaining -= 256;
}
return ret;
}