Date: Mon, 04 Jun 2001 19:17:30 -0700 From: Mike Smith <msmith@freebsd.org> To: John Polstra <jdp@polstra.com> Cc: alpha@freebsd.org Subject: Re: SCSI devices settling and illegal request Message-ID: <200106050217.f552HUL07003@mass.dis.org> In-Reply-To: Your message of "Mon, 04 Jun 2001 18:56:30 PDT." <200106050156.f551uUx40794@vashon.polstra.com>
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> > > Modern server-class alphas (such as DS20, xp1000, AS4100, AS4000,
> > > AS1200, etc) may have totally separate PCI buses, with separate IO =
and
> > > memory spaces. Like a normal bus, each of these can have ppbs to
> > > child busses, etc. We call each collection of buses a hose. This
> > > terminology comes from the SRM console.
> > =
> > Just FWIW, you will see this in the PC world as well at some point; I=
ntel =
> > call them "channels" (personally, I think "hose" is a much cooler nam=
e).
> =
> There's something I'm still not clear about. I've been working lately
> with an x86 motherboard that has two separate PCI buses -- one 66 MHz
> bus and one 33 MHz bus. What would be different if these were "hoses"
> or "channels"? Is it that they would have separate address spaces?
Each "hose" is a scope container for the PCI resources, ie. bus numbers,
mapping addresses, etc.
On the x86 systems you're using, there are two busses, and they are =
separately bridged off the processor, but they share the same PCI bus =
numbering space, and there's only one address space. If you had two =
channels, each channel would have its own PCI bus #0, and you could have =
a device on each channel with a mapping at 0xe4000000, without either =
conflicting. (Typically each hose has a window and mappings are relative=
=
to the base of that window.)
Hoses were one way of getting around the 4GB addressability limit with PC=
I
(amongst other things); 64-bit PCI and DAC (double address cycle) are
others that have more currency right now.
-- =
=2E.. 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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