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This simple document only needs a markup for its title to be using the standard we're adopting for text documents. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
25 lines
994 B
Plaintext
25 lines
994 B
Plaintext
===============
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What is an IRQ?
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===============
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An IRQ is an interrupt request from a device.
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Currently they can come in over a pin, or over a packet.
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Several devices may be connected to the same pin thus
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sharing an IRQ.
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An IRQ number is a kernel identifier used to talk about a hardware
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interrupt source. Typically this is an index into the global irq_desc
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array, but except for what linux/interrupt.h implements the details
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are architecture specific.
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An IRQ number is an enumeration of the possible interrupt sources on a
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machine. Typically what is enumerated is the number of input pins on
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all of the interrupt controller in the system. In the case of ISA
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what is enumerated are the 16 input pins on the two i8259 interrupt
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controllers.
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Architectures can assign additional meaning to the IRQ numbers, and
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are encouraged to in the case where there is any manual configuration
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of the hardware involved. The ISA IRQs are a classic example of
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assigning this kind of additional meaning.
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