Messages in this thread | | | Date | Sun, 29 Feb 2004 09:36:57 +0100 | From | Arjan van de Ven <> | Subject | Re: Why no interrupt priorities? |
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On Sun, Feb 29, 2004 at 04:32:54PM +0800, Michael Frank wrote: > > Most interrupt controllers can read back IRQ's to see whether it is > active. A shared IRQ would be readback active while any device > connected to it desires service. > > x86 example for 8259A AT-PIC's Returns the state of IRQ0-15 in ax > Note that jmp $+2 is only needed on some old 286/386 hardware > to meet (real) 8259A cycle time requirements. > > - Intel syntax :) > > mov al,0ah > out 0a0h,al > jmp $+2 > in al,0a0h > mov ah,al > mov al,0ah > jmp $+2 > out 20h,al > jmp $+2 > in al,20h
interesting; however with modern cpus I suspect that a series of in/outs like that is more expensive than one or two "surious" hardirq handler calls...
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