1What is an IRQ?
   3An IRQ is an interrupt request from a device.
   4Currently they can come in over a pin, or over a packet.
   5Several devices may be connected to the same pin thus
   6sharing an IRQ.
   8An IRQ number is a kernel identifier used to talk about a hardware
   9interrupt source.  Typically this is an index into the global irq_desc
  10array, but except for what linux/interrupt.h implements the details
  11are architecture specific.
  13An IRQ number is an enumeration of the possible interrupt sources on a
  14machine.  Typically what is enumerated is the number of input pins on
  15all of the interrupt controller in the system.  In the case of ISA
  16what is enumerated are the 16 input pins on the two i8259 interrupt
  19Architectures can assign additional meaning to the IRQ numbers, and
  20are encouraged to in the case  where there is any manual configuration
  21of the hardware involved.  The ISA IRQs are a classic example of
  22assigning this kind of additional meaning.