1=============== 2What is an IRQ? 3=============== 4 5An IRQ is an interrupt request from a device. 6Currently they can come in over a pin, or over a packet. 7Several devices may be connected to the same pin thus 8sharing an IRQ. 9 10An IRQ number is a kernel identifier used to talk about a hardware 11interrupt source. Typically this is an index into the global irq_desc 12array, but except for what linux/interrupt.h implements the details 13are architecture specific. 14 15An IRQ number is an enumeration of the possible interrupt sources on a 16machine. Typically what is enumerated is the number of input pins on 17all of the interrupt controller in the system. In the case of ISA 18what is enumerated are the 16 input pins on the two i8259 interrupt 19controllers. 20 21Architectures can assign additional meaning to the IRQ numbers, and 22are encouraged to in the case where there is any manual configuration 23of the hardware involved. The ISA IRQs are a classic example of 24assigning this kind of additional meaning. 25