Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
The generic feature model is represented in the following block diagram. In this model the generic
feature is described to OSPM through AML code. This description takes the form of an object that
sits in the ACPI Namespace associated with the hardware to which it is adding value.
ACPI Driver
and AML-
Interpreter
Rds
AML
Events
GP Event Status
Generic Child
Event Status
Generic Event
Logic
Control
Generic
Control
Logic
Figure 4-9 Generic Hardware Feature Model
As an example of a generic hardware control feature, a platform might be designed such that the IDE
HDD’s D3 state has value-added hardware to remove power from the drive. The IDE drive would
then have a reference to the AML PowerResource object (which controls the value added power
plane) in its namespace, and associated with that object would be control methods that OSPM
invokes to control the D3 state of the drive:
• _PS0: A control method to sequence the IDE drive to the D0 state.
• _PS3: A control method to sequence the IDE drive to the D3 state.
• _PSC: A control method that returns the status of the IDE drive (on or off).
The control methods under this object provide an abstraction layer between OSPM and the
hardware. OSPM understands how to control power planes (turn them on or off or to get their status)
through its defined PowerResource object, while the hardware has platform-specific AML code
(contained in the appropriate control methods) to perform the desired function. In this example, the
platform would describe its hardware to the ACPI OS by writing and placing the AML code to turn
the hardware off within the _PS3 control method. This enables the following sequence:
When OSPM decides to place the IDE drive in the D3 state, it calls the IDE driver and tells it to
place the drive into the D3 state (at which point the driver saves the device’s context).
When the IDE driver returns control, OSPM places the drive in the D3 state.
OSPM finds the object associated with the HDD and then finds within that object any AML code
associated with the D3 state.
OSPM executes the appropriate _PS3 control method to control the value-added “generic” hardware
to place the HDD into an even lower power state.
As an example of a generic event feature, a platform might have a docking capability. In this case, it
will want to generate an event. Notice that all ACPI events generate an SCI, which can be mapped to
any shareable system interrupt. In the case of docking, the event is generated when a docking has
been detected or when the user requests to undock the system. This enables the following sequence:
60 April, 2015 Version 6.0