Messages in this thread | | | From | Mike Frysinger <> | Subject | Re: [PATCH 2/8] firmware: Sigma: Skip header during CRC generation | Date | Tue, 29 Nov 2011 00:11:38 -0500 |
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On Monday 28 November 2011 02:56:33 Lars-Peter Clausen wrote: > On 11/25/2011 09:00 PM, Mike Frysinger wrote: > > On Friday 25 November 2011 03:55:42 Lars-Peter Clausen wrote: > >> On 11/24/2011 06:21 PM, Mike Frysinger wrote: > >>> On Thursday 24 November 2011 07:48:21 Lars-Peter Clausen wrote: > >>>> The firmware header is not part of the CRC, so skip it. Otherwise the > >>>> firmware will be rejected due to non-matching CRCs. > >>> > >>> that's because you didn't compare to the right value ;). include the > >>> CRC -> compare to 0. omit the CRC -> compare to the CRC value. > >> > >> Does this really work if the CRC is inserted somewhere in the middle of > >> the bytestream? > > > > i don't think the position matters to the CRC algorithm used by sigmadsp. > > math principle: a ^ b ^ c is the same thing as b ^ a ^ c and c ^ b ^ a. > > If CRC algorithms were commutative they would be pretty weak, I guess ;)
that doesn't stop people from implementing them this way ;). the last CRC code i did actually implement and test related to the Blackfin arch did have this property (the bootrom). so i just included the computed CRC value and made sure the end result is 0.
> > i could be wrong as to the CRC algo used though. simple enough for you > > to check -- i implemented this firmware code based on a spec i wrote up > > for the sigmadsp peeps; i never actually had real firmware to test with. > > It does not work.
ok, i withdraw my complaints here then :) -mike [unhandled content-type:application/pgp-signature] | |