piclist 2002\05\12\025929a >
Thread: Looking for an efficient CRC
face BY : Ashley Roll email (remove spam text)

Hi Tal,

> Is there a good CRC or error detection mechanism that can be
> consume only
> few instructions for each byte of data ?  Somebody mention to
> us that we can
> speed up algorithms such as CRC16 using lookup tables but I
> don't think the
> 12c508 can hold tables of decent size.

I was probably the one you were thinking of. I suggested that one could
implement a table based CRC16 using tables less then 256 items in a
discussion about a week ago.

For instance you could build a CRC16 that updates 4 bits per time using two
16 element tables. This is 32 instructions for data plus a few extra
instructions to do the jump into the table. This should easily fit on the
first code page in a 12C805 if you haven't got any other tables you should
be fine.

I've not actually tried to implement this technique yet, but it should work.
From a quick "Guess-timate" of the algorithm it will probably be somewhere
in the order of 50-70 instruction cycles per byte to update the CRC..

Is that going to be fast enough?

Maybe its time I actually tried to implement this..


Ashley Roll
Digital Nemesis Pty Ltd
Mobile: +61 (0)417 705 718

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<00cb01c1f982$8dca13a0$641010ac@tardis> 7bit

See also: www.piclist.com/techref/method/errors.htm?key=crc

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