RE: Gottlieb / Q*bert scripts for the 9010A/9100

>
> Just for the fun of it I wrote a quick program that tried all
> possible feedback
> combinations for 16 bit CRCs (65536 combinations), none of them
> generated the
> proper signatures, so it's more than just a variation of the standard CRC
> calculations.

Ah-ha! BUT!! Did you try for all possible combinations of /starting/ CRC?
Try that 'just for fun' - it should only take 65536 times as long :-)

In my old serial comms days, we always started our CRC's at some bizarre
number (3403 IIRC), for two reasons 1) it offered better data security of
our protocols and 2) because it was safer to start there as some random
numbers are better generators than others.

If you run a mathematical random number generators over a long period then
you get less random bits that others (i.e. the numbers stay about the same
for a while). This is the same for CRC's and thus the safety of the
calculation in spotting single or double bit errors is dimished in certain
areas.

> Anybody know of two different ROMs, or byte streams that result
> in the same
> signature?

There's loads in ROMIdent - just run with a bunch of EPROMS from your MAME
directory, and you're bound to find a couple.

Cheers,
Phillip Eaton
Received on Wed May 08 16:54:23 2002