Silly Question: Difference between PIC and APIC?
Exquisitus V-man
From the reading i have done so far, the PIC (1 & 2) controls IRQ 0-15
w. Each PIC handles 8 IRQs, but the second is routed through the frist at
IRQ2. That i understand. How does the APIC fits into the picture which
handles INT 0 - 0xFF? I started reading the Intel Volume 3 manual and it
seems only to deals with the APIC.
Thanks.
.v
KVP
The apics were designed to replace the existing pics. There are two kinds
of apics. There is one in each modern x86 cpu, and there could be i/o apics
on the motherboard. The job of this system is to provide irq routing and
smp communication between cpus. The extended hardware irq range is just an
extra. Each apic aware motherboard has a compatibility mode, where the
system emulates the old pic behaviour. The system starts in this
compatibility mode.
Viktor
Exquisitus V-man
Thanks, I am getting it. So I could really avoid the legacy stuff by just
programming teh APIC (if i will be running on i586 and up)?. I would much
rather that, than all of this routing of IRQs and all that stuff. Thanks,
i will just focus on the Intel doc for APIC.
.v
KVP
Unfortunately, some older PII-PIII motherboards don't have the i/o apic
(the motherboard side of the apic set), so you must use the compatibility
mode. However, it's easy to set up the old pics, all you need is 8 i/o
writes to set the operation modes and the irq base numbers. Setting up an
apic is much harder, but you will have to do it to be able to use the other
cpus on your motherboard. (single cpu boards may still lack the i/o apic)
Viktor
ps:
Intel has designed a new timer circuit, but still uses the old legacy
pit, so it's better to support older legacy stuff.
Maxim S. Shatskih
by just
> programming teh APIC (if i will be running on i586 and up)?. I
would much
Note that legacy PIC is not yet obsolete, for instance, Pentium III
machines (i815 chipset and such) still use it.
Max