/* ---------------------------------------------------------------------------- | |
* SAM Software Package License | |
* ---------------------------------------------------------------------------- | |
* Copyright (c) 2012, Atmel Corporation | |
* | |
* All rights reserved. | |
* | |
* Redistribution and use in source and binary forms, with or without | |
* modification, are permitted provided that the following conditions are met: | |
* | |
* - Redistributions of source code must retain the above copyright notice, | |
* this list of conditions and the disclaimer below. | |
* | |
* Atmel's name may not be used to endorse or promote products derived from | |
* this software without specific prior written permission. | |
* | |
* DISCLAIMER: THIS SOFTWARE IS PROVIDED BY ATMEL "AS IS" AND ANY EXPRESS OR | |
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF | |
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT ARE | |
* DISCLAIMED. IN NO EVENT SHALL ATMEL 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. | |
* ---------------------------------------------------------------------------- | |
*/ | |
/*---------------------------------------------------------------------------- | |
* Headers | |
*----------------------------------------------------------------------------*/ | |
#include "board.h" | |
/*---------------------------------------------------------------------------- | |
* Internal function | |
*----------------------------------------------------------------------------*/ | |
/** | |
* Counts and return the number of bits set to '1' in the given byte. | |
* \param byte Byte to count. | |
*/ | |
static uint8_t CountBitsInByte(uint8_t byte) | |
{ | |
uint8_t count = 0; | |
while (byte > 0) | |
{ | |
if (byte & 1) | |
{ | |
count++; | |
} | |
byte >>= 1; | |
} | |
return count; | |
} | |
/** | |
* Counts and return the number of bits set to '1' in the given hamming code. | |
* \param code Hamming code. | |
*/ | |
static uint8_t CountBitsInCode256(uint8_t *code) | |
{ | |
return CountBitsInByte(code[0]) + CountBitsInByte(code[1]) + CountBitsInByte(code[2]); | |
} | |
/** | |
* Calculates the 22-bit hamming code for a 256-bytes block of data. | |
* \param data Data buffer to calculate code for. | |
* \param code Pointer to a buffer where the code should be stored. | |
*/ | |
static void Compute256(const uint8_t *data, uint8_t *code) | |
{ | |
uint32_t i; | |
uint8_t columnSum = 0; | |
uint8_t evenLineCode = 0; | |
uint8_t oddLineCode = 0; | |
uint8_t evenColumnCode = 0; | |
uint8_t oddColumnCode = 0; | |
// 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++) | |
{ | |
columnSum ^= 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 ((CountBitsInByte(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, evenLineCode and oddLineCode, such as | |
// evenLineCode bits: P128 P64 P32 P16 P8 P4 P2 P1 | |
// oddLineCode bits: P128' P64' P32' P16' P8' P4' P2' P1' | |
// | |
evenLineCode ^= (255 - i); | |
oddLineCode ^= i; | |
} | |
} | |
// At this point, we have the line parities, and the column sum. First, We | |
// must caculate the parity group values on the column sum. | |
for (i=0; i < 8; i++) | |
{ | |
if (columnSum & 1) | |
{ | |
evenColumnCode ^= (7 - i); | |
oddColumnCode ^= i; | |
} | |
columnSum >>= 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 ((oddLineCode & 0x80) != 0) | |
{ | |
code[0] |= 2; | |
} | |
if ((evenLineCode & 0x80) != 0) | |
{ | |
code[0] |= 1; | |
} | |
// Line 2 | |
if ((oddLineCode & 0x08) != 0) | |
{ | |
code[1] |= 2; | |
} | |
if ((evenLineCode & 0x08) != 0) | |
{ | |
code[1] |= 1; | |
} | |
// Column | |
if ((oddColumnCode & 0x04) != 0) | |
{ | |
code[2] |= 2; | |
} | |
if ((evenColumnCode & 0x04) != 0) | |
{ | |
code[2] |= 1; | |
} | |
oddLineCode <<= 1; | |
evenLineCode <<= 1; | |
oddColumnCode <<= 1; | |
evenColumnCode <<= 1; | |
} | |
// Invert codes (linux compatibility) | |
code[0] = (~(uint32_t)code[0]); | |
code[1] = (~(uint32_t)code[1]); | |
code[2] = (~(uint32_t)code[2]); | |
TRACE_DEBUG("Computed code = %02X %02X %02X\n\r", | |
code[0], code[1], code[2]); | |
} | |
/** | |
* Verifies and corrects a 256-bytes block of data using the given 22-bits | |
* hamming code. | |
* | |
* \param data Data buffer to check. | |
* \param originalCode Hamming code to use for verifying the data. | |
* | |
* \return 0 if there is no error, otherwise returns a HAMMING_ERROR code. | |
*/ | |
static uint8_t Verify256( uint8_t* pucData, const uint8_t* pucOriginalCode ) | |
{ | |
/* Calculate new code */ | |
uint8_t computedCode[3] ; | |
uint8_t correctionCode[3] ; | |
Compute256( pucData, computedCode ) ; | |
/* Xor both codes together */ | |
correctionCode[0] = computedCode[0] ^ pucOriginalCode[0] ; | |
correctionCode[1] = computedCode[1] ^ pucOriginalCode[1] ; | |
correctionCode[2] = computedCode[2] ^ pucOriginalCode[2] ; | |
TRACE_DEBUG( "Correction code = %02X %02X %02X\n\r", correctionCode[0], correctionCode[1], correctionCode[2] ) ; | |
// If all bytes are 0, there is no error | |
if ( (correctionCode[0] == 0) && (correctionCode[1] == 0) && (correctionCode[2] == 0) ) | |
{ | |
return 0 ; | |
} | |
/* If there is a single bit error, there are 11 bits set to 1 */ | |
if ( CountBitsInCode256( correctionCode ) == 11 ) | |
{ | |
// Get byte and bit indexes | |
uint8_t byte ; | |
uint8_t bit ; | |
byte = correctionCode[0] & 0x80; | |
byte |= (correctionCode[0] << 1) & 0x40; | |
byte |= (correctionCode[0] << 2) & 0x20; | |
byte |= (correctionCode[0] << 3) & 0x10; | |
byte |= (correctionCode[1] >> 4) & 0x08; | |
byte |= (correctionCode[1] >> 3) & 0x04; | |
byte |= (correctionCode[1] >> 2) & 0x02; | |
byte |= (correctionCode[1] >> 1) & 0x01; | |
bit = (correctionCode[2] >> 5) & 0x04; | |
bit |= (correctionCode[2] >> 4) & 0x02; | |
bit |= (correctionCode[2] >> 3) & 0x01; | |
/* Correct bit */ | |
TRACE_DEBUG("Correcting byte #%d at bit %d\n\r", byte, bit ) ; | |
pucData[byte] ^= (1 << bit) ; | |
return Hamming_ERROR_SINGLEBIT ; | |
} | |
/* Check if ECC has been corrupted */ | |
if ( CountBitsInCode256( correctionCode ) == 1 ) | |
{ | |
return Hamming_ERROR_ECC ; | |
} | |
/* Otherwise, this is a multi-bit error */ | |
else | |
{ | |
return Hamming_ERROR_MULTIPLEBITS ; | |
} | |
} | |
/*---------------------------------------------------------------------------- | |
* Exported functions | |
*----------------------------------------------------------------------------*/ | |
/** | |
* Computes 3-bytes hamming codes for a data block whose size is multiple of | |
* 256 bytes. Each 256 bytes block gets its own code. | |
* \param data Data to compute code for. | |
* \param size Data size in bytes. | |
* \param code Codes buffer. | |
*/ | |
void Hamming_Compute256x( const uint8_t *pucData, uint32_t dwSize, uint8_t* puCode ) | |
{ | |
TRACE_DEBUG("Hamming_Compute256x()\n\r"); | |
while ( dwSize > 0 ) | |
{ | |
Compute256( pucData, puCode ) ; | |
pucData += 256; | |
puCode += 3; | |
dwSize -= 256; | |
} | |
} | |
/** | |
* 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. | |
* | |
* \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. | |
* | |
* \param data Data buffer to verify. | |
* \param size Size of the data in bytes. | |
* \param code Original codes. | |
*/ | |
uint8_t Hamming_Verify256x( uint8_t* pucData, uint32_t dwSize, const uint8_t* pucCode ) | |
{ | |
uint8_t error ; | |
uint8_t result = 0 ; | |
TRACE_DEBUG( "Hamming_Verify256x()\n\r" ) ; | |
while ( dwSize > 0 ) | |
{ | |
error = Verify256( pucData, pucCode ) ; | |
if ( error == Hamming_ERROR_SINGLEBIT ) | |
{ | |
result = Hamming_ERROR_SINGLEBIT ; | |
} | |
else | |
{ | |
if ( error ) | |
{ | |
return error ; | |
} | |
} | |
pucData += 256; | |
pucCode += 3; | |
dwSize -= 256; | |
} | |
return result ; | |
} | |