|What is an IRQ?
|An IRQ is an interrupt request from a device.
|Currently they can come in over a pin, or over a packet.
|Several devices may be connected to the same pin thus
|sharing an IRQ.
|An IRQ number is a kernel identifier used to talk about a hardware
|interrupt source. Typically this is an index into the global irq_desc
|array, but except for what linux/interrupt.h implements the details
|are architecture specific.
|An IRQ number is an enumeration of the possible interrupt sources on a
|machine. Typically what is enumerated is the number of input pins on
|all of the interrupt controller in the system. In the case of ISA
|what is enumerated are the 16 input pins on the two i8259 interrupt
|Architectures can assign additional meaning to the IRQ numbers, and
|are encouraged to in the case where there is any manual configuration
|of the hardware involved. The ISA IRQs are a classic example of
|assigning this kind of additional meaning.