Re: [Qemu-devel] [PATCH v2 0/7] APIC/IOAPIC cleanup

[Anthony Liguori]

On 08/19/2010 05:52 PM, malc wrote:
> > Yes, but the programming model was different.
> >
> > Look at the PIC compared to the lapic.  The PIC is programmed via pio at a
> > fixed location.  There is only one PIC and it interacts with the system just
> > like all other devices.  IOW, there is no reference to CPUState.
> >      
> There are two PICs actually there's a cascade..
>    

Technically speaking, originally there was just one and then more IRQs 
were supported by cascading and reserving an IRQ line for supporting 
cascading.  I think you can technical cascade with any IRQ and have more 
than one slave but the historic PC architecture only had one slave AFAIK.

Regards,

Anthon Liguori

> > When you look at the local APIC (apic.c) however, you see that it's the only
> > device in the tree that actually interacts with a CPUState.  The notion of
> > cpu_get_current_apic() is a good example of the tricks needed to make this
> > work.
> >
> > The local APIC is a cpu feature, not a device.
> >
> > Regards,
> >
> > Anthony Liguori
> >
> >      
>