assigning interrupts

[John Baldwin]

On Thursday 13 November 2008 10:40:03 am Joerg Sonnenberger wrote:
> On Thu, Nov 13, 2008 at 02:40:54AM -0800, Jeremy Chadwick wrote:
> > Otherwise, consider purchasing a motherboard that has an APIC (this is
> > not a typo) increasing the IRQ count to 256.
> 
> This is wrong. The first IO-APIC gives you 8 additional interrupts to
> the 16 ISA interrupt lines. Every additional IO-APIC gives you 24 more.
> Most modern chipsets have one IO-APIC, at least for non-embedded
> systems. It doesn't mean you don't get interrupt sharing though.

I/O APICs are not hardwired to 24 pins.  Early Pentium SMP systems actually 
only had 16 pins on their I/O APICs.  I've seen I/O APICs with 32 pins, etc.  
There is a register in the I/O APIC that lets software know how many pins it 
contains.

-- 
John Baldwin