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

[Lars-Peter Clausen <lars@metafoo.de>]

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 ;)
> 
> 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

It does not work.

- Lars