[tulip] Problems with IRQs on multiport cards

[Donald Becker]

On Wed, 13 Sep 2000, Jonathan Earle wrote:

> > The INT-to-IRQ mapping is unique to the specific motherboard. 
> >  Only the motherboard BIOS can set up the mapping, including configuring
> the PCI
> > bridge on the multiport card.
> 
> What do you mean by INT to IRQ mapping?  I thought that an INT(errupt?) and
> an IRQ were the same thing, yes?

No.  An INT (INTA..INTD) is a PCI interrupt pin.
An IRQ is an interrupt request level.
ISA interrupt pins mapped directly to processor IRQs.
A motherboard has an arbitrary mapping from INT pins to logical IRQs.

> The reason I asked was that the code for the de4x5 driver had a function to
> request an IRQ (called from the init code), and perhaps I read it
> incorrectly, but it appeared as though one could pick an IRQ (say 4) and
> then request that from the BIOS (essentially determining via the BIOS, if
> the IRQ was free).  I tried hacking around in there, but it didn't work (I
> didn't get the IRQ I specifically wanted).

The de4x5 driver supports EISA cards.
Perhaps you were looking at the EISA support code.

> > Verify that the interrupt count is increasing for each port.  
> > It may be that only eth0 is generating interrupts.
> 
> How do I verify the interrupt count - 'cat /proc/interrupt'?  If so, the
> counts are increasing, however, eth0, eth1 and eth4 (eth1 is the traffic
> ingress and eth4 is the egress) are all on the same IRQ.  Eth0 is actually a
> builtin 3COM 59x port but doesn't carry a lot of traffic.  Eth1-4 are on the
> multiport card, and the count for the IRQ associated with eth3 (eth2 is not
> configured) increments as well as the count for eth0/1/4.

Send traffic only on eth1.
  Verify that the interrupt count increases proportional to the packet count.
Send traffic only on eth2.
  Verify that the interrupt count increases proportional to the packet count.
etc.

Donald Becker				becker@scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Beowulf-II Cluster Distribution
Annapolis MD 21403