> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
Behalf
> Of Scott Dattalo
> Sent: 24 February 2010 18:36
> To: Microcontroller discussion list - Public.
> Subject: Re: [PIC] Reduce CRC size
> 
> > Not technically a PIC but an ARM Cortex part with a neat built in 32
bit
> > CRC calculator.
> 
> Here's a 5 instruction ARM implementation of the CRC-CCITT polynomial
x^16
> + x^15 + x^5 + 1:
> 
> ; R0[7:0] = input data, R1[15:0] = input and output crc.
>    eor R0,R0,R1 LSR 8  ; R0 = t = (crc0 >> 8) ^ data
>    eor R0,R0,R0 LSR 4  ; R0 = t ^ (t >> 4)
>    eor R1,R0,R1 LSL 8  ; R1 = (crc0 << 8) ^ t
>    eor R1,R1,R0 LSL 5  ; R1 = (crc0 << 8) ^ t ^ (t << 5)
>    eor R1,R1,R0 LSL 12 ; R1 = (crc0 << 8) ^ t ^ (t << 5) ^ (t << 12)
> 
> It's an implementation of
> 
> http://www.dattalo.com/technical/software/pic/crc_1021.asm
> 
> I must admit though, I never did test the ARM implementation.

Thanks Scott, that's a very nice implementation.  I'll give it a go in
the simulator.
 
Mike

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