RE: PCI interruptions between two PCI expansion boards

[Richard Walter <rwalter@brocade.com>]

Michael,

Simple answer: no

Longer answer: The PCI spec leaves the routing of the interrupt lines from slots completely up to the motherboard designer.  (Aside: This is why there are IntPin & IntLine registers in config space.  IntPin is the method which the device tells the configuration software on the board which INT[A,B,C,D]# is used and IntLine is the method which the configuration software tells the drivers how it's hooked up on the motherboard (under the assumption that the configuration software has intimate knowledge of the motherboard.))

I have seen designs over the last 6 years that have:
* Connect all INTA#'s together; Connect all INTB#'s together; etc...
* Connect INT[A,B,C,D]# of slot 0 together;
  Connect INT[A,B,C,D]# of slot 1 together; etc...
* Connect Slot 0-INTA# to Slot 1-INTB# to Slot 2-INTC#, etc... ;
  Connect Slot 0-INTB# to Slot 1-INTC# to Slot 2-INTD#, etc...
  etc...

As a card vendor, you have no control or knowledge of the physical routing and connectivities of the INTx# lines.

Possible solution:  However, one possible solution is to have a little stub of a driver running on the host CPU.  When one card issues an interrupt, that stub could then write to a register in the second board to let it know that the interrupt occurred.  You probably ought to beef this basic structure up with protection against things like a second interrupt occuring before the first is forwarded and other such "edge cases".

Finally, if you really want card-to-card interrupts, you may want to run a small jumper cable between the cards.  Either inside of the case (which is out-of-the-way of users, or outside of the case through the PCI bracket (which is more architecturally clean, but has the greater possibility of the cable being pulled out.

-Richard Walter
rwalter@brocade.com
Note: I speak for myself, not for Brocade.

-----Original Message-----
From: michael.pellegrino@modicon.com
[mailto:michael.pellegrino@modicon.com]
Sent: Wednesday, March 07, 2001 6:37 AM
To: pci-sig@znyx.com
Subject: PCI interruptions between two PCI expansion boards


Are there any possibilities to generate interruptions between two PCI expansion
boards (for exemple a master/slave board software wanting to interrupt a slave
board software or vice versa)  through the use of INTA# pin according to the PCI
standard ?

Thanks in advance.