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Date:      Tue, 15 Oct 2002 11:51:58 -0400 (EDT)
From:      Andrew Gallatin <gallatin@cs.duke.edu>
To:        Peter Wemm <peter@wemm.org>
Cc:        arch@FreeBSD.org
Subject:   Re: Database indexes and ram 
Message-ID:  <15788.14750.474882.99633@grasshopper.cs.duke.edu>
In-Reply-To: <20021015011435.763AE2A88D@canning.wemm.org>
References:  <3DAA695F.96E345E6@mindspring.com> <20021015011435.763AE2A88D@canning.wemm.org>

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Peter Wemm writes:
 > Terry Lambert wrote:
 > > Peter Wemm wrote:
 > > > And then there's the AGP remap table stuff to provide a window from
 > > > anywhere in memory into the lower 4G of space that's within reach of 32 bit
 > > > PCI devices...
 > > 
 > > Peter, you are sneaky... in a good way.
 > > 
 > > Do you really think this could be abused this way?  How much, in the
 > > way of windows, can you have lying around at one time?  I'm not very
 > > AGP-aware, other than "I need it for my X server".
 > 
 > I cant claim credit for this.. The linux folks supposedly have it working - 
 > David O'Brien told me about it.
 > 

FWIW, Doug Rabson thought of this a few years ago when we first ported
FreeBSD/alpha to the API UP1x000.  Unlike most alphas, it has an AGP
slot, and it does not have a pci chipset capable of doing
scatter/gather dma mapping.   Doug suggested that I use the AGP remap
table for ISA dma, but I could never make it work.  I ended up just
doing bounce buffers.

Drew

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