Advanced Configuration and Power Interface Specification

ACPI Software Programming Model
• PNP0C0C — Power Button Device
• PNP0C0D — Lid Device
• PNP0C0E — Sleep Button Device
2. PCI Bus Wakeup Event Reporting (PME)
• PNP0A03 — PCI Host Bridge
All wake events that are not exclusively tied to a GPE input (for example, one input is shared for
multiple wake events) must have individual enable and status bits in order to properly handle the
semantics used by the system.
5.6.4.2.1 Managing a Wake Event Using Device _PRW Objects
A device’s _PRW object provides the zero-based bit index into the general-purpose status register
block to indicate which general-purpose status bit from either GPE0_BLK or GPE1_BLK is used as
the specific device’s wake mask. Although the hardware must maintain individual device wake
enable bits, the system can have multiple devices using the same general-purpose event bit by using
OEM-specific hardware to provide second-level status and enable bits. In this case, the OEM AML
code is responsible for the second-level enable and status bits.
OSPM enables or disables the device wake function by enabling or disabling its corresponding GPE
and by executing its _PSW control method (which is used to take care of the second-level enables).
When the GPE is asserted, OSPM still executes the corresponding GPE control method that
determines which device wakes are asserted and notifies the corresponding device objects. The
native OS driver is then notified that its device has asserted wake, for which the driver powers on its
device to service it.
If the system is in a sleeping state when the enabled GPE bit is asserted the hardware will transition
the system into the S0 state, if possible.
5.6.4.2.2 Determining the System Wake Source Using _Wxx Control Methods
After a transition to the S0 state, OSPM may evaluate the _SWS object in the \_GPE scope to
determine the index of the GPE that was the source of the transition event. When a single GPE is
shared among multiple devices, the platform provides a _Wxx control method, where xx is GPE
index as described in Section 5.6.4.2.2, that allows the source device of the transition to be
determined. If implemented, the _Wxx control method must exist in the \_GPE scope or in the scope
of a GPE block device.
If _Wxx is implemented, either hardware or firmware must detect and save the source device as
described in Section 7.4.3, “_SWS (System Wake Source)”. During invocation, the _Wxx control
method determines the source device and issues a Notify(,0x2) on the device that caused
the system to transition to the S0 state. If the device uses a bus-specific method of arming for
wakeup, then the Notify must be issued on the parent of the device that has a _PRW method. The
_Wxx method must issue a Notify(,0x2) only to devices that contain a _PRW method
within their device scope. OSPM’s evaluation of the _SWS and _Wxx objects is indeterminate. As
such, the platform must not rely on _SWS or _Wxx evaluation to clear any hardware state, including
GPEx_STS bits, or to perform any wakeup-related actions.
If the GPE index returned by the _SWS object is only referenced by a single _PRW object in the
system, it is implied that the device containing that _PRW is the wake source. In this case, it is not
necessary for the platform to provide a _Wxx method.
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