On 11/27/05, Paul Davis <paul@xxxxxxxxxxxxxxxxxxxxx> 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. (TTBOMK) > 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
