Re: Hands on PCI interface ...
From: keith (krw_at_att.bizzzz)
Date: 02/03/05
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Date: Wed, 02 Feb 2005 21:45:32 -0500
On Wed, 02 Feb 2005 19:00:33 +0000, Jonathan Kirwan wrote:
> On Thu, 3 Feb 2005 04:26:11 +1100, <Nico> wrote:
>
>>Interfacing via ISA bus is very easy but slow and it is getting difficult to
>>find ISA based PCs.
>
> This is the reason I keep ISA bus based PCs around and working.
>
>>USB bus easy to use but its packet stucture and therefore the latency is an
>>issue for some real-time applications.
>>
>>So, I want to learn how to build and work/play with PCI interfaces. Can you
>>suggest what is the easiest and low-cost way of involving with the PCI bus
>>to learn with hands on experiments?
>
> Well, ponying up to PCI will not be cheap. First, you need to understand the
> difference between reflection wave and incident wave -- PCI is reflection wave.
You really don't have to get into it in that detail unless you're pushing
the envelope.
> Second, there are very tight constraints implied by the technology. Your
> PCI clock line must be 1.5" +/- 0.1" in length,
2.5" +- /1", though that isn't generally a problem. For a product, sure.
> signal lines are to be less than 2.5" (if memory serves),
Must be less than .75", IIRC. They really need to be as short as
possible. 2.5" likely *won't* work. Stubs are badness!
> and you will often find weird
> serpentine clock lines to meet that 1.5" requirement.
Yes, almost always (2.5").
> Third, because of
> the loading requirements (at 33MHz, some 10pF total; at 66Mhz, 5pF), you
> will be using an ASIC. No discrete logic with multiple loads on single
> lines, for example.
Yes, and the receivers aren't typical CMOS. Many FPGAs have PCI I/O.
Either is a bad plan for one-off designs though. As mentioned before in
this thread, PLX bridges are the way to go. They have PCI<->ISA brifges
that work quite well. There are also PCI<->ISA cards.
> Fourth, you will pay much more dearly for
> instruments that can monitor and display PCI bus signals.
Not really true. There are some relatively cheap bus monitors. If one
sticks to a known bridge design a scope is all that's needed. I got a
PLX-9054 based card running with no more than a scope.
> Fifth, PCI mandates plug-and-play and certain minimum register
> requirements and the ability to assign block addresses, if needed.
Another reason to go with a known design. ;-)
> You can get low cost ASICs.
Not ASICs. ASSPs (Application Specific Standard Products).
> But the rest makes this not low-cost and
> there is a high threshold of knowledge required, as well. PCI was
> almost designed from the ground up to exclude basement developers.
Designed to exclude? Are you implying that they intentionally raised the
entry bar? That's some charge! There is a reason for complication. It
makes life simpler. ;-)
-- Keith
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