| ??? 11/02/06 06:26 Read: times |
#127246 - Checksum of what? Responding to: ???'s previous message |
James Corbin said:
Hi, I'm using an Atmel 8051 derivative without a built-in global checksum read ability. What is a "global checksum read ability"? Usually, only CODE space is checksummed (because it's only meaningful there) and any checking/reporting of it would have to be done by the code that you write. More commonly, the checksum would be checked by some external device (eg, a PROM programmer) What 8051 derivative does have a "global checksum read ability"? execute at startup and store the result in RAM (later being transmitted to the PC terminal). Usually, the checksum is stored in the ROM itself, and is such that performing the check operation over the whole ROM should result in a value of zero - if it doesn't, you know you've got an error! There is a fundamental flaw here: if you accept the likelihood that your ROM will fail, how can you rely on your own code (whih must be stored in that same ROM) to check itself? What happens if the ROM error happens to be somewhere within the checksum validation code... 1) Is a 32-bit CRC the typical checksum format used for something like this? Not clear exactly what you mean, so not sure what would be "normal" for it! Usually, ROM checks are just 16-bit simple checksums 2) For something like a 64k part, how long does this typically take to execute? Don't know, but a 32-bit CRC is obviously going to take longer that a 16-bit simple checksum... |
