27 Nov
2005
27 Nov
'05
11:44 a.m.
On 11/27/05, Paul Davis <paul(a)linuxaudiosystems.com> wrote:
On Sat, 2005-11-26 at 17:40 -0800, Mark Knecht wrote:
This is true. APIC inputs != IRQs. If a PC (laptop, desktop, etc.)
uses an APIC then the idea is that each hardware device can have it's
own input on the APIC and eventually it's own APIC IRQ.
However, if a PC (laptop, desktop, etc.) shares interrupts going into
an APIC then these (TTBOMK) cannot be separated. If they are the same
trace on the motherboard then they map to a single shared IRQ.
(TTBOMK)
Changing interrupt priorities of internal devices
on a laptop is not
possible. The devices are on the motherboard and are hard wired to
specific inputs on the PIC. You cannot change them at all.
i am not sure that this is strictly true. my impression of modern intel-
based architecture is that the inputs to the (A)PIC do not map
deterministically to IRQ lines feeding the CPU. the (A)PIC and its
cousins can be programmed to do many different things. the problem with
laptops is generally that they come with a BIOS that offers no options
to "reprogram" the (A)PIC, and then you boot into a kernel that
generally seems to want to leave this stuff alone. this is increasingly
the case on non-laptops as well, which is quite depressing.
You raise a very valuable point. Whether using a PIC or an APIC some
BIOS's do allow the user to:
1) Disable the APIC in favor of an old style PIC
2) Change the IRQ number of a limited number of internal hardware devices.
As far as I know Linux does leave BIOS IRQ settings alone, or can be
told to.Possibly thewade should look at what BIOS control, if any, his
machine gives him.
- Mark