Date: Thu, 13 Aug 1998 22:20:38 -0700 (PDT) From: asami@FreeBSD.ORG (Satoshi Asami) To: tom@uniserve.com Cc: scrappy@hub.org, freebsd-current@FreeBSD.ORG Subject: Re: More PCI Slots... (fwd) Message-ID: <199808140520.WAA12851@silvia.hip.berkeley.edu> In-Reply-To: <Pine.BSF.3.96.980813105242.19010D-100000@shell.uniserve.ca> (message from Tom on Thu, 13 Aug 1998 10:57:25 -0700 (PDT))
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* > > PCI extender boxes have been available for a long time. Not long ago
* > > there was a mention of someone who hooked several of these up to a FreeBSD
* > > system.
That was probably me. We daisy-chained couple of the Bit3 boxes (7
slots each) and put a twin-channel SCSI adapter at the far end. It
worked on some of our machines.
* > The OS doesn't need to do anything special to recognize them? Are
* > there any limitations?
The BIOS needs to set up the bridge chips correctly. Note that there
can be a full tree of these things hooked up to each other, so it has
to recurse into the buses correctly to set up the PCI bus ID registers
and such. Obviously there is some point it will stop working if you
keep daisy-chaining the boxes because there is only a limited amount
of memory the BIOS can use.
At the time we tested (more than 3 years ago), Award BIOS didn't work
with more than one level of bridging. All of them worked with
twin-channel adapters (one bridge in there too) in the host PCI bus
though, so they did know about bridge chips.
* It is part of the PCI standard. PCI-PCI bridging.
I think the chip has to be recognized correctly. Stefan added ours
(the IBM chip) to the list.
* > At work, we are looking at a Sparc Enterprise 450, which has 10PCI
* > slots spread over something like 3-4 PCI busses...do the extende do
* > something like that, or is it all one big bus?
*
* I belive each extender is considered a separate bus, but of course is
* linked back to whatever bus it is plugged into. However, some x86
* motherboards have their PCI slots slit over two buses too.
There are usually 4 or 5 slots per bus. And the host-expansion cable
is also a separate bus. So, for instance, a 7-slot expansion box
(which actually only adds 6 slots because one of the host PCI slots is
taken) plugged into a 4-slot host will look like this (`*'s are the
bridge chips):
host
| bus 0 bus 2 bus 3
+-+-+-+ +-+-+-+ * +-+-+-+
| | | | | | | | | | | |
* *
+---------+
bus 1
^
|
this slot is for the host interface card only
Satoshi
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