Mark Knecht wrote: > No, you are exactly right. Clemens and I have some small technical > disagreements on this subject. We had a conversation that was > interesting but I think didn't yield any clear answers, at least in my > mind, so I freely admit I'm still confused on the subject. > > [...] As I remember the conversation the interrupt order was from > the highest interrupt number and going down from there, so if > Florin sees 25 interrupts, then #25 gets serviced first and that > would be where I'd want my sound card, if I could get it there. What I tried to explain was that the priority is not determined by the interrupt number but by the interrupt vector number. Well, let's see if my explanation isn't too muddy this time :-) The routing of interrupts from the hardware to the driver happens on three levels. First, there are the (PCI) interrupt lines, which are the input pins of the interrupt controller chip. These are usually called PIRQA/B/C... The only way to choose the interrupt line for the sound card is to put it into another PCI slot. The interrupt line of integrated devices is usually fixed. The interrupt controller (PIC or I/O-APIC) has a number of hardware interrupts (PIC 16, I/O-APIC 24? or more). Each interrupt line is mapped to one interrupt. In PIC mode, the routing of interrupt line to interrupt number can be chosen by software (but is done by the BIOS in practice). In I/O-APIC mode, the routing of interrupt lines to interrupts is fixed: each PCI interrupt line gets one of the interrupts above 15. These are the interrupt numbers shown in /proc/interrupts. The interrupts are mapped to interrupt vectors. Intel CPUs have 256 of them, but some are used for other purposes than hardware interrupts. The interrupt vector numbers are chosen by the Linux kernel, and are fairly well hidden, but you can find them in the dmesg output if I/O-APIC is enabled. When the I/O-APIC is not enabled, interrupt priority is determined by the interrupt number (0 1 8 9 10 11 12 13 14 15 3 4 5 6 7). When the I/O-APIC is enabled, interrupt priority is determined by the interrupt vector number (lower vectors numbers have higher priority). (My patch to change vector numbers doesn't work with current kernels.) Regards, Clemens
