Programming Embedded Systems in C and C++

Working with Flash Memory 79

/**********************************************************************

*

* Function: crcCompute()

*

* Description: Compute the CRC checksum of a binary message block.

*

* Notes: This function expects that crcInit() has been called

* first to initialize the CRC lookup table.

*

* Returns: The CRC of the data.

*

**********************************************************************/

width

crcCompute(unsigned char * message, unsigned int nBytes)

{

unsigned int offset;

unsigned char byte;

width remainder = INITIAL_REMAINDER;

/*

* Divide the message by the polynomial, a byte at a time.

*/

for (offset = 0; offset < nBytes; offset++)

{

byte = (remainder >> (WIDTH - 8)) ^ message[offset];

remainder = crcTable[byte] ^ (remainder << 8);

}

/*

* The final remainder is the CRC result.

*/

return (remainder ^ FINAL_XOR_VALUE);

} /* crcCompute() */

Working with Flash Memory

From the programmer’s viewpoint, Flash is arguably the most complicated mem-

ory device ever invented. The hardware interface has improved somewhat since

the original devices were introduced in 1988, but there is still a long way to go.

Reading from Flash memory is fast and easy, as it should be. In fact, reading data

from a Flash is not all that different from reading from any other memory device.

*

The processor simply provides the address, and the memory device returns the

data stored at that location.