An Intro to Edge-Triggered Interrupts
Some device adapters generate an interrupt by driving their respective IRQ (Interrupt Request) signal line from an electrical low to an electrical high. In this case, the input on the interrupt controller must be programmed to recognize the rising-edge of the input signal as a valid interrupt request.
Generally speaking, an IRQ signal line that works in this manner cannot be shared by multiple device adapters. The interrupt controller (i.e., the IO APIC) would recognize the first interrupt request, set the IRR bit (Interrupt Request Register bit) and will be ready to recognize another valid request immediately after the first had been dispatched to the processor and the IRR bit cleared.
It is illegal for ...
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