Scott Dattalo <piclist@mit.edu> wrote:

> > You'll need to be pretty tricky to do the CRC in realtime along
> > with banging the bus at 4 (or 8) MHz. 
> 
> If you tell me the polynomial and provide a few examples of CRC'd
> data, then I'll take a whack at an efficient implementation. An
> 8-bit polynomial should take no more than about 20 instruction
> cycles. If there's symmetry that can be exploited, then it may take
> fewer.

... And if you're bit-banging a serial interface so you already have 
access to your data one bit at a time, you can do it in 4 cycles per 
bit (RLF CRC / MOVLW poly / SKPNC / XORWF CRC) -- or maybe 3 cycles 
per bit if you can avoid having to reload W for every bit.  It's 
slower than doing it a whole byte at a time, but it takes less code 
space and might make the timing a lot easier. 

-Andrew

=== Andrew Warren - fastfwd@ix.netcom.com

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