Hi Ashley,

I looked at your code and it looks great. I think this will work for us. We
can either CRC the entire message before we start sending it. This will
delay the message a little bit but I think it will be OK.

Great contribution to the list!

Tal

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Ashley Roll
> Sent: Saturday, May 11, 2002 11:59 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: Looking for an efficient CRC
>
>
> 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..
>
> Cheers,
> Ash.
>
> ---
> Ashley Roll
> Digital Nemesis Pty Ltd
> www.digitalnemesis.com
> Mobile: +61 (0)417 705 718
>
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