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Date:      Fri, 30 Jul 1999 02:34:34 -0700
From:      Mike Smith <mike@smith.net.au>
To:        Stephen Hocking-Senior Programmer PGS Tensor Perth <shocking@prth.pgs.com>
Cc:        current@freebsd.org
Subject:   Re: MTRR stuff 
Message-ID:  <199907300934.CAA02191@dingo.cdrom.com>
In-Reply-To: Your message of "Fri, 09 Jul 1999 10:32:37 %2B0800." <199907090232.KAA04002@ariadne.tensor.pgs.com> 

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> For some video cards (to wit, the voodoo stuff), the MTRRs should be set up as 
> follows
> 
>    write-combining
>  +----------------------------------------------------------+ 
>  +-------+
>   uncacheable
> 
> i.e. the two regions have the same starting area, but the small chunk for the 
> registers should be uncacheable. When I try to do this using memconf on my 
> K6-2, it spits the dummy. Is there a work around for this?

The i686 MTRR implementation, at least, doesn't allow UC to overlap WC; 
only Write-back and uncached are allowed to overlap.  I don't know what 
the K6's limitations are; you should talk to Brian Feldman about that.

-- 
\\  The mind's the standard       \\  Mike Smith
\\  of the man.                   \\  msmith@freebsd.org
\\    -- Joseph Merrick           \\  msmith@cdrom.com




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