[oc] Modular FPGA Board: PCI

[John Dalton <john.dalton@bigfoot.com>]

Thanks for the comments so far.

As mentioned in my previous post, the "PCI" connector on the main
board is not meant to comply with the PCI electrical specification.
I guess I should really call it a "PCI like" connector.

To clarify the situation, I have put a couple more block diagrams
on the web ( http://www.elec.mq.edu.au/~jdalton/modularfpga/ )
and modified the original diagram to make it plain that the connector is
non-compliant.

If a compliant PCI interface is required, a second board must be built as shown
in drawing "MPCI1".  Apart from achieving compliance, putting the
PCI interface in a separate FPGA allows the main FPGA
to be reconfigured over the PCI bus.

What is the use of a non-compliant PCI connector?  I needed
some sort of connection to a host interface board, so I thought
I might as well make it as close to PCI as possible.  Under certain
conditions (such as not installing the SIMMs), this *MIGHT* make it
possible to do a "PCI" interface on the main FPGA.  (Though from what
people are saying, it sounds unlikely that this non-compliant connector will work
as true PCI.)  Of course if guaranteed compliance is required you must build the
second board.

Why not put a compliant PCI interface directly on the main board?
1) Many users will not require PCI.  With SIMMs on the "PCI" lines,
they can put the "PCI" pins to use.
2) If using a separate FPGA, the PCI FPGA can be upgraded independently
from the main FPGA
3) The PCI interface can be replaced with any other type of interface
(eg. a block diagram of an ISA interface is given in drawing MISA1.)

I hope this clarifies things.  Please keep the comments coming!

Answering specific questions:

> Or do you want to use either memory (and no pci) or pci (and
> no memory) ?
Only one at a time.

> Can I find some log file of this discussion on some Web?
An archive is on http://www.opencores.org/

Regards
John

PS.  Please let me know if my postscript diagrams don't work.
They view okay for me using gnome-gv. I've only just started using dia.