Advanced Configuration and Power Interface Specification

Device Configuration
Field Type Description
Pin Byte The PCI pin number of the device (0–INTA, 1–INTB, 2–INTC, 3–INTD).
Source NamePath
Or
Byte
Name of the device that allocates the interrupt to which the above pin is connected.
The name can be a fully qualified path, a relative path, or a simple name segment
that utilizes the namespace search rules. Note: This field is a NamePath and not a
String literal, meaning that it should not be surrounded by quotes. If this field is the
integer constant Zero (or a Byte value of 0), then the interrupt is allocated from the
global interrupt pool.
Source
Index
DWORD
Index that indicates which resource descriptor in the resource template of the
device pointed to in the Source field this interrupt is allocated from. If the Source
field is the Byte value zero, then this field is the global system interrupt number to
which the pin is connected.
There are two ways that _PRT can be used. Typically, the interrupt input that a given PCI interrupt is
on is configurable. For example, a given PCI interrupt might be configured for either IRQ 10 or 11
on an 8259 interrupt controller. In this model, each interrupt is represented in the ACPI namespace
as a PCI Interrupt Link Device.
These objects have _PRS, _CRS, _SRS, and _DIS control methods to allocate the interrupt. Then,
OSPM handles the interrupts not as interrupt inputs on the interrupt controller, but as PCI interrupt
pins. The driver looks up the device’s pins in the _PRT to determine which device objects allocate
the interrupts. To move the PCI interrupt to a different interrupt input on the interrupt controller,
OSPM uses _PRS, _CRS, _SRS, and _DIS control methods for the PCI Interrupt Link Device.
In the second model, the PCI interrupts are hardwired to specific interrupt inputs on the interrupt
controller and are not configurable. In this case, the Source field in _PRT does not reference a
device, but instead contains the value zero, and the Source Index field contains the global system
interrupt to which the PCI interrupt is hardwired.
6.2.13.1 Example: Using _PRT to Describe PCI IRQ Routing
The following example describes two PCI slots and a PCI video chip. Notice that the interrupts on
the two PCI slots are wired differently (barber-poled).
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