From f702d7013c7470284843a6370aaa53b8b75c5a40 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Thu, 29 Jun 2006 02:25:02 -0700 Subject: [PATCH] [PATCH] genirq: irq: document what an IRQ is Signed-off-by: Eric W. Biederman Cc: Ingo Molnar Cc: Thomas Gleixner Cc: Benjamin Herrenschmidt Cc: Rajesh Shah Cc: Andi Kleen Cc: "Protasevich, Natalie" Cc: "Luck, Tony" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/IRQ.txt | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) create mode 100644 Documentation/IRQ.txt diff --git a/Documentation/IRQ.txt b/Documentation/IRQ.txt new file mode 100644 index 00000000000..1011e717502 --- /dev/null +++ b/Documentation/IRQ.txt @@ -0,0 +1,22 @@ +What is an IRQ? + +An IRQ is an interrupt request from a device. +Currently they can come in over a pin, or over a packet. +Several devices may be connected to the same pin thus +sharing an IRQ. + +An IRQ number is a kernel identifier used to talk about a hardware +interrupt source. Typically this is an index into the global irq_desc +array, but except for what linux/interrupt.h implements the details +are architecture specific. + +An IRQ number is an enumeration of the possible interrupt sources on a +machine. Typically what is enumerated is the number of input pins on +all of the interrupt controller in the system. In the case of ISA +what is enumerated are the 16 input pins on the two i8259 interrupt +controllers. + +Architectures can assign additional meaning to the IRQ numbers, and +are encouraged to in the case where there is any manual configuration +of the hardware involved. The ISA IRQs are a classic example of +assigning this kind of additional meaning.