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

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Date:	Fri, 25 Nov 2011 15:00:50 -0500
From:	Mike Frysinger <vapier@...too.org>
To:	"Lars-Peter Clausen" <lars@...afoo.de>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, alsa-devel@...a-project.org,
	drivers@...log.com, stable@...nel.org
Subject: Re: [PATCH 2/8] firmware: Sigma: Skip header during CRC generation

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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