summaryrefslogtreecommitdiff
path: root/Documentation/IRQ.txt
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/IRQ.txt')
-rw-r--r--Documentation/IRQ.txt22
1 files changed, 22 insertions, 0 deletions
diff --git a/Documentation/IRQ.txt b/Documentation/IRQ.txt
new file mode 100644
index 000000000..1011e7175
--- /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.