Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
Step
OS View of power
states
8 OS resumes on Core1 Core0: Running
Core1: Running
Cluster0: Running
Platform view of
power states
Core0: Running
Core1: Running
Cluster0: Running
As before, once control is returned to the OS, it can handle as it sees fit – likely just re-requesting the
idle state on both cores.
8.4.4.3 _LPI (Low Power Idle States)
_LPI is an optional object that provides a method to describe Low Power Idle states that defines the
local power states for each node in a hierarchical processor topology. The OSPM uses the _LPI
object to select a local power state for each level of processor hierarchy in the system. These local
state selections are then used to produce a composite power state request that is presented to the
platform by the OSPM.
This object may be used inside a Processor Container or a processor declaration. _LPI takes the
following format:
Arguments:
None
Return Value:
A variable-length Package containing the local power states for the parent Processor or Processor
Container device as described in the table following below. _LPI evaluation returns the below
format:
Package {
Revision, // Integer (WORD)
LevelID, // Integer (QWORD)
Count, // Integer (WORD)
LPI[1], // Package
…
LPI[N] // Package
}
Element Object Type Description
Revision Integer The revision number of the _LPI object. Current revision is 0.
(WORD)
LevelID Integer
(QWORD)
A platform defined number that identifies the level of hierarchy of the processor
node to which the LPI states apply. This is used in composition of IDs for OS
Initiated states described in Section 8.4.4.3.4. In a platform that only supports
platform coordinated mode, this field must be 0.
Count Integer The count of following LPI packages.
(WORD)
LPI[1] Package A Package containing the definition of LPI state 1.
LPI[N] Package A Package containing the definition of LPI state N.
444 April, 2015 Version 6.0