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Interrupts (IRQ)
The XEN-LS II (like every other ISA compatible PC)
supports 15 hardware interrupts. These interrupts are used
to alert the processor that a peripheral (e.g. the keyboard
controller, or an expansion card) requires a particular piece
of software to be executed. This piece of software is known
as an interrupt service routine .
Each peripheral has a unique interrupt service routine that
is executed in response to the interrupt assigned to that
peripheral.
When an interrupt occurs the processor stops executing its
current task, executes the interrupt service routine, then
returns to its original task. The processor is, literally,
interrupted.
A hardware interrupt may be referred to as an IRQ. This is
because the motherboard signals used to generate the
interrupts are labelled IRQ x where x is a number between 0
and 15, excluding 2.
Note
In an ISA compatible system if you select IRQ2 on an
expansion card it uses IRQ9. This means that if an
expansion card is using IRQ2, no other card can use
IRQ9.
Some interrupts are assigned to standard functions and are
essential for the operation of the board. Examples of these
are, IRQ0 which is used to maintain the system time, and
IRQ13 which is used by the coprocessor.
Selecting IRQs for cards
The table below lists the interrupts available on the
motherboard and their default functions. The notes explain
whether the default function can be disabled, if so how, and
under what circumstances it is safe to do so.
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