[Asterisk-Users] Generic X100P's

[Kevin P. Fleming]

Steven Critchfield wrote:

> Funny since there is only 4 real IRQ lines on a PCI bus. They are A, B,
> C, and D. If you have more than 4 slots on a PCI bus, then you are most
> definately reusing a real IRQ wire. 

That is a drastic oversimplification; each PCI slot has only four IRQ 
lines, but there is nothing that says that the lines have to be 
connected together between the slots. The first PCI boards were that 
way, but the spec does not mandate that they be interconnected.

On many current motherboards (especially server boards), they are not. 
All the IRQ lines from each slot go _separately_ to an APIC on the 
motherboard, where they are then routed as needed. For "simple" 
operating systems (those that don't support APIC routing), you end up 
with multiple devices sharing IRQs. Linux has the smarts to use the APIC 
to its full potential, so you can have all the devices (including the 
onboard NIC, sound, RAID, etc.) on separate IRQs. I have lots of systems 
working this way, and it's very nice.

Try compiling your kernel with APIC and IO-APIC support (including 
"local APIC support for uniprocessors") and see how it improves the IRQ 
routing in your system.