RE: PCI clock distributuion..

[John Bush <john.bush@emrad.com>]

I may be on the wrong track here.  If so just ignore.

A PICMG Passive PCI backplane SBC has enough Request/Grant/Clock signals to
control four PCI slots.  The SBC fits into a dedicated slot that happens to
look the same as all the others.

If you've only got 4 sets of control lines you can only really have 4
"slots" eg one bridge and three physical slots or two bridges and two
physical slots.

I'd see this as the limiting factor rather than loading/propagation issues.
Unless you're after non bus master slots.

Regards
John