Simple but reliable checksum for small controllers

Tilmann Reh · 2008-06-09T07:38:12+00:00

Hello,for an integrity check of the program code for small controller (8051derivatives), I am looking for an efficient checksum method.The code size will be max. 32k, and a standard 8051 (X2) should manageto calculate the checksum in a reasonable time (no significant delay atpower-up, say max. 500 ms). Faster devices (like the LPC900) will havesome advantage here, additionally due to the smaller code memory...Just adding (or XORing) the code bytes to a 16/24/32-bit sum is simpleand fast, but not too reliable in case of multi-bit errors at the samebit position.For calculating a CRC with 16 or more bits, the required table wouldneed too much code memory - or doing it by shifting would take too muchtime.I now thought of calculating two different sums. One by simply addingall code bytes to a 16 bit sum, the other by adding the byte and thenshifting the sum one bit. This would reduce the probability of notfinding a two-bit error to 1/16 compared to a single sum.Are there other methods (easy to implement in small code, fast andreliable) I should consider?Thanks,Tilmann

Jun 09, 2008 21 Replies

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Tauno Voipio 18 years ago

Hello,

I sent mail to your posting address.

If it does not work, please send a mail with a good address to me. Modify the address in my sig in the obvious way to send.

Tauno Voipio tauno voipio (at) iki fi

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Tilmann Reh 18 years ago

Tauno Voipio schrieb:

If you sent it to the "from" address, it probably will be lost - despammed.com is not too reliable meanwhile.

That's why I added a working "reply-to" address (which doesn't get spammed as much as "from" addresses).

About CRC-16: Maxim also have a direct algorithm in their AN27 (Example

6, 8051 assembly). Looks quite interesting... Maybe the same method as yours?

Thanks, Tilmann

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