Re: tlug: Re: PCI [was: dual-pentium processors]

[Karl-Max Wagner <karlmax@example.com>]

> What exactly does the PCI spec dictate?  My friend made it sound like
> they basically mandated an impedance mismatch/improper termination.  I'm

That alone is already bad enough. Scenario: you have a driver
looking into a line with a Zo = 70 ohms. Termination is 150
ohms. It happens that some idiot designer designed the driver
for being able to drive 150 ohms ONLY. However, what does the
driver see at the first instant ? 70 ohms. result: driver
overload and a staircased waveform which may or may not be
within specs. Further result: erratic operation difficult to
track down.

> working on something using industrial single board computers and passive
> PCI backplanes, and this talk is making me nervous.  I'm going to need

Well, PCI works....kinda. It's not a great scheme, though.
However, you're not gonna have much choice, anyway. If they want
PCI, they want it. Full stop. You just have the option to make
the best out of it.

However, check a bit how competent your vendor is in terms of rf
engineering. Don't let them scare you by the usual big talk they use to
impress people. Dig up what they REALLY know. Maybe use a scope
and check their bus design.

However, if you have the option of selecting VME instead, go for
that ! It's a much better design. However, I fear they won't
like the price tag.....

> to select a passive PCI backplane vendor here shortly....
> 
> Any more info or references, Karl-Max?  My RF experience is limited to

OK. Stay tuned. I try to dig it up ASAP.

> ham radio and sophomore EE courses (yikes! both around 15 years ago).

I have been a ham for 22 years, too. I learned a lot that way.

Email me privately if you need more detailed info. It's a bit
far from Linux - although I don't dobt that it might be of
interest to quite a few people.

                                    Karl-Max Wagner
                                    karlmax@example.com
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