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Documentation / IRQ.txt




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Based on kernel version 3.9. Page generated on 2013-05-02 23:09 EST.

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