[linux-audio-user] IRQ conflicts, acpi, and linux audio
markknecht at gmail.com
Sun Nov 27 10:44:30 EST 2005
On 11/27/05, Paul Davis <paul at linuxaudiosystems.com> wrote:
> On Sat, 2005-11-26 at 17:40 -0800, Mark Knecht wrote:
> > 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.
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.
> 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.
More information about the Linux-audio-user