Advanced Configuration and Power Interface Specification

Processor Configuration and Control
}
//
// Note: The UUID passed into _OSC is CPU vendor specific. Consult CPU
// vendor documentation for UUID and Capabilities Buffer bit definitions
//
_OSC (ToUUID("4077A616-290C-47BE-9EBD-D87058713953"), REVS, SIZE, Local2)
Section 6.2.11, “_OSC (Operating System Capabilities)”, describes the _OSC object, which can be
used to convey processor related OSPM capabilities to the platform. Consult CPU vendor specific
documentation for the UUID and Capabilities Buffer bit definitions used by _OSC for a specific
processor.
8.4.2 Processor Power State Control
ACPI defines multiple processor power state (C state) control interfaces. These are:
1. The Processor Register Block’s (P_BLK’s) P_LVL2 and P_LVL3 registers coupled with FADT
P_LVLx_LAT values and
2. The _CST object in the processor’s object list.
3. The _LPI objects for processors and processor containers.
P_BLK based C state controls are described in Section 4, “ACPI Hardware Specification” and
Section 8.1, “Processor Power States”. _CST based C state controls expand the functionality of the
P_BLK based controls allowing the number and type of C states to be dynamic and accommodate
CPU architecture specific C state entry and exit mechanisms as indicated by registers defined using
the Functional Fixed Hardware address space.
_CST is an optional object that provides:
• The Processor Register Block's (P_BLK's) P_LVL2 and P_LVL3 registers coupled with FADT
P_LVLx_LAT values.
• The _CST object in the processor's object list.
ACPI 6.0 introduces _LPI, the low power idle state object. _LPI provides more detailed power state
information and can describe idle states at multiple levels of hierarchy in conjunction with Processor
Containers. See Section 8.4.4.3 for details.
8.4.2.1 _CST (C States)
_CST is an optional object that provides an alternative method to declare the supported processor
power states (C States). Values provided by the _CST object override P_LVLx values in P_BLK and
P_LVLx_LAT values in the FADT. The _CST object allows the number of processor power states
to be expanded beyond C1, C2, and C3 to an arbitrary number of power states. The entry semantics
for these expanded states, (in other words), the considerations for entering these states, are conveyed
to OSPM by the C-state Type field and correspond to the entry semantics for C1, C2, and C3 as
described in Section 8.1.2 through Section 8.1.4. _CST defines ascending C-states characterized by
lower power and higher entry/exit latency.
Arguments:
None
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