Calculate/verify ROM checksum

[stevev]

How do I calculate a checksum of the flash ROM in a 16F877 device? From the manual it appears that the compiler will set environment variable ID to the rom checksum at program time if you use the "#ID CHECKSUM" directive, and you can access the stored ID with GETENV(ID), but how do you calculate the checksum at run time when starting up to verify all is the same as when the chip was programmed?

I didn't see this discussed in prior posts so any help would be most appreciated.

Thanks, -steve-
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This message was ported from CCS's old forum
Original Post ID: 11943

[Jon Fick]

The CCS manual shows the following that is applicable only to devices that can read from program memory using the read_program_eeprom command.

checksum = 0;
for(i=0; i<8196; i++)
{
checksum^=read_program_eeprom(i);
}
printf("Checksum is \%2X\r\n",checksum);

Jon
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This message was ported from CCS's old forum
Original Post ID: 11955

[stevev]

Thanks, I tried that but the value I get doesn't match the ID retrieved with "#ID CHECKSUM". Looking at the Microchip stuff it seems the checksum they expect in the hex file is a 12-bit sum. Does that mean masking each word to 12-bits before adding? Or masking off the total to 12-bits? None of these things seem to work.

Does anybody have any code where they have done this before? I'm just stabbing in the dark trying to perform what should be a simple check.

Any help or code would be appreciated! -steve-

:=The CCS manual shows the following that is applicable only to devices that can read from program memory using the read_program_eeprom command.
:=
:=checksum = 0;
:=for(i=0; i<8196; i++)
:= {
:= checksum^=read_program_eeprom(i);
:= }
:=printf("Checksum is \%2X\r\n",checksum);
:=
:=Jon
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This message was ported from CCS's old forum
Original Post ID: 11960