Re: [PATCH 2/8] firmware: Sigma: Skip header during CRC generation

From: Mike Frysinger
Date: Fri Nov 25 2011 - 15:02:50 EST


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.

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.
-mike

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