Very Computer

Hello,

Can anyone explain to me the method of arranging PCI cards on a backplane
with multiple PCI buses.

I remember reading that there are only a few IRQs assigned to the PCI bus,
and that cards must be arranged in such a way that cards can share them,
initially this hasn't been a problem, but now I'm setting up a machine with
12 PCI slots and 8 ISA slots and oddly enough getting enough IRQ's is quite
hard :-)

Any guesses ?

For reference I want the following in my machine :

Dual Pentium SBC (2 * 200MMX) on board EIDE & IO

Miranda DigiLinx (ISA)
Matrox DigiMix (PCI)
Matrox DigiMotion (PCI)
Matrox DigiDesktop (PCI)
 - These four cards are linked together with a Movie-2 bus and cannot be
split up

Emulex Fibre Channel Card (PCI)
Specialix SX (PCI)
3Com 3c90x (PCI)
Digital Audio Labs V8 (ISA)
TimeCode generator (ISA)

Regards

Mark

Hi Mark!

What is the type of that board? Is there docu in the web?

Quote:> but now I'm setting up a machine with
> 12 PCI slots and 8 ISA slots and oddly enough getting enough IRQ's is > quite hard :-)

It indeed is with standard Intel chipsets.

But I would expect that a board with 12 PCI Slots has more IRQ
controllers (PIC) than a 0815 DOSe. IRQ sharing on the ISA BUS is as
good as impossible. (Totem-pole outputs, not open collector). From the
idea of PCI each PCI slot on the primary bus should have 4 _OWN_ IRQ
lines. There is no HW reason not to put 12 PICs onto a board. They can
be cascaded.

If there are PCI to PCI bridge chips which build secondary PCI busses
the 4 Primary IRQ lines from the slot which the Bridge chip occupies are
rotated between the secondary slots.

Quote:> Any guesses ?

What does your BIOS say? My Award bios shows me which device got which
IRQ. Do you have a circuit diagram of that board?

--
Bernd Harries

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