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