st72F521 checksum problem

[julien239955_stm1_st]

Posted on June 14, 2007 at 07:36

st72F521 checksum problem

[julien239955_stm1_st]

Posted on June 12, 2007 at 12:31

Hi,

I'm in front of a problem by the using of a function which should give the checksum of my software.

#ifdef USE_HDFLASH_CHECKSUM

/*-----------------------------------------------------------------------------

ROUTINE NAME : HDFlashChecksum

INPUT : Flash address, Frequency

OUTPUT : Embedded Command Status

Returned values of Checksum are in EMBLG_PARAM_ENDH and

EMBLG_PARAM_ENDL addresses

DESCRIPTION : Compute a Checksum

-----------------------------------------------------------------------------*/

unsigned char HDFlashChecksum(unsigned char *Flash, unsigned char Freq)

{

EMBLG_PARAM_ECMD = 0x06;

EMBLG_PARAM_PTRL = ((int)Flash & 0xFF); // Flash Address Low Byte

EMBLG_PARAM_PTRH = ((int)Flash >> 8); // Flash Address High Byte

EMBLG_PARAM_FREQ = Freq;

FCSR = 0x00; // Launch command (no need to wait end of operation)

return EMBLG_PARAM_ECMD; // Return Embedded Command Status

}

#endif

How can I know the ''Flash Address Low Byte'' of my soft? So what should be the value of ''Flash''?

thanks for your help

[wolfgang2399]

Posted on June 14, 2007 at 07:36

Hi,

although I don't really comprehend your problem in detail, I'll try to give some ideas.

Declaring the EMBLG_PARAM_PTR as pointer to an unsigned character with

char *EMBLG_PARAM_PTR;

you'll get the two byte number EMBLG_PARAM_PTR as pointer to an unsigned char.

To calculate the checksum you only have to add all the values of your flash from the first to the last byte.

checksum = 0;

 

for(EMBLG_PARAM_PTR = FLASH_FIRST_BYTE; EMBLG_PARAM_PTR <= FLASH_LAST_BYTE;) checksum += *(EMBLG_PARAM_PTR++);

where FLASH_FIRST_BYTE and FLASH_LAST_BYTE are constant pointers to the first and to the last byte of your flash.

But pay attention: If FLASH_LAST_BYTE == 0xFFFF you'll meet a serious problem: Increasing EMBLG_PARAM_PTR (== 0xFFFF) causes an overrun to 0x0000. Then the query EMBLG_PARAM_PTR <= FLASH_LAST_BYTE will give a wrong result and you might enter a deadloop!!!

In this case better use

checksum = 0;

 

for(EMBLG_PARAM_PTR = FLASH_LAST_BYTE; EMBLG_PARAM_PTR >= FLASH_FIRST_BYTE;) checksum += *(EMBLG_PARAM_PTR--);

Alternatively to declared constants you might take numerical constants as addresses:

checksum = 0;

 

for(EMBLG_PARAM_PTR = (unsigned char*)0xFFFF; EMBLG_PARAM_PTR >= (unsigned char*)0x8000;) checksum += *(EMBLG_PARAM_PTR--);

Hope it will help you to find a solution,

WoRo