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f702d701 EB |
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. |