Re: PYXIS bug detection

From: Jay Estabrook (Jay.Estabrook@compaq.com)
Date: Fri Dec 14 2001 - 10:33:06 EST


On Thu, Dec 13, 2001 at 11:26:05PM +0100, Kurt Garloff wrote:
> On Thu, Dec 13, 2001 at 04:57:03PM -0500, Jay Estabrook wrote:
>
> > > My docs say it should be possible to have 6GB. Don't know if that's
> > > actually true.
> >
> > Yes, theoretically. I think 3GB has been done, in which case one would
> > have trouble without S/G DMA window support. Most likely the practical
> > limit is 1.5GB.
>
> I think that even up to 4GB should not be a problem, as that's the size of
> 32bits and the size of the monster window, no?

Um, well, not as I understand it.

Monster window is only available when using DAC, ie 64-bit PCI addresses.
Only some controllers are able to do this, and only *some* of *them* can
actually do it on Alpha: the monster window may need more bits of address
to "get to" (ie 39 bits) than the card can actually generate (an example
being an Adaptec which can only generate 36-bit DAC addresses).

I'd be real surprised if *any* IDE controllers can actually do DAC... ;-}

--Jay++

-----------------------------------------------------------------------------
Jay A Estabrook Alpha Engineering - LINUX Project
Compaq Computer Corp. - MRO1-2/K15 (508) 467-2080
200 Forest Street, Marlboro MA 01752 Jay.Estabrook@compaq.com
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