Date: Thu, 02 Aug 2001 20:52:09 -0700 From: Mike Smith <msmith@freebsd.org> To: Kenneth Wayne Culver <culverk@wam.umd.edu> Cc: Julian Elischer <julian@elischer.org>, John Baldwin <jhb@FreeBSD.ORG>, freebsd-hackers@FreeBSD.ORG, craig <craiglei@pasia.com.cn>, Terry Lambert <tlambert2@mindspring.com>, Rik van Riel <riel@conectiva.com.br> Subject: Re: How to visit physical memory above 4G? Message-ID: <200108030352.f733q9C01482@mass.dis.org> In-Reply-To: Your message of "Thu, 02 Aug 2001 14:55:28 EDT." <Pine.GSO.4.21.0108021454210.20844-100000@rac2.wam.umd.edu>
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> > No
> > The space is linear in physical space and if you have PCI/64
> > capable devices they can access it all too.
> >
> > (In fact 64 bit addresses have been supported even in 32 bit wide PCI
> > since day 1).
>
> OK, then what was that whole paging thing everyone was talking about, I
> thought that was partially done in hardware on the chipset of the
> motherboard... or was that completely in the operating system?
Julian is on crack. DAC (Double Address Cycle) is a relatively recent
addition to PCI that allows 32-bit cards with 64-bit savvy logic to talk
to host memory using 64-bit target addresses.
Older systems used a scatter-gather mechanism to present a virtualised
view of the system's physical address space to the PCI bus (typically
you'll see this in Alpha systems).
--
... every activity meets with opposition, everyone who acts has his
rivals and unfortunately opponents also. But not because people want
to be opponents, rather because the tasks and relationships force
people to take different points of view. [Dr. Fritz Todt]
V I C T O R Y N O T V E N G E A N C E
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