0001 ===============
0002 What is an IRQ?
0003 ===============
0004
0005 An IRQ is an interrupt request from a device.
0006 Currently they can come in over a pin, or over a packet.
0007 Several devices may be connected to the same pin thus
0008 sharing an IRQ.
0009
0010 An IRQ number is a kernel identifier used to talk about a hardware
0011 interrupt source. Typically this is an index into the global irq_desc
0012 array, but except for what linux/interrupt.h implements the details
0013 are architecture specific.
0014
0015 An IRQ number is an enumeration of the possible interrupt sources on a
0016 machine. Typically what is enumerated is the number of input pins on
0017 all of the interrupt controller in the system. In the case of ISA
0018 what is enumerated are the 16 input pins on the two i8259 interrupt
0019 controllers.
0020
0021 Architectures can assign additional meaning to the IRQ numbers, and
0022 are encouraged to in the case where there is any manual configuration
0023 of the hardware involved. The ISA IRQs are a classic example of
0024 assigning this kind of additional meaning.
