Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
P_BLK based throttling state controls are described in Section 4, “ACPI Hardware Specification”
and Section 8.1.1, “Processor Power State C0”. Combined _PTC, _TSS, and _TPC based throttling
state controls expand the functionality of the P_BLK based control allowing the number of T states
to be dynamic and accommodate CPU architecture specific T state control mechanisms as indicated
by registers defined using the Functional Fixed Hardware address space. While platform definition
of the _PTC, _TSS, and _TPC objects is optional, all three objects must exist under a processor for
OSPM to successfully perform processor throttling via these controls.
8.4.5.1 _PTC (Processor Throttling Control)
_PTC is an optional object that defines a processor throttling control interface alternative to the I/O
address spaced-based P_BLK throttling control register (P_CNT) described in Section 4, “ACPI
Hardware Specification”. The processor throttling control register mechanism remains as defined in
Section 8.1.1, “Processor Power State C0.”
OSPM performs processor throttling control by writing the Control field value for the target
throttling state (T-state), retrieved from the Throttling Supported States object (_TSS), to the
Throttling Control Register (THROTTLE_CTRL) defined by the _PTC object. OSPM may select
any processor throttling state indicated as available by the value returned by the _TPC control
method.
Success or failure of the processor throttling state transition is determined by reading the Throttling
Status Register (THROTTLE_STATUS) to determine the processor’s current throttling state. If the
transition was successful, the value read from THROTTLE_STATUS will match the “Status” field
in the _TSS entry that corresponds to the targeted processor throttling state.
Arguments:
None
Return Value:
A Package as described below
Return Value Information
Package
{
}
ControlRegister
StatusRegister
Table 8-244 PTC Package Values
// Buffer (Resource Descriptor)
// Buffer (Resource Descriptor)
Element Object Type Description
Control
Register
Status
Register
Buffer
Buffer
Contains a Resource Descriptor with a single Register() descriptor that
describes the throttling control register.
Contains a Resource Descriptor with a single Register() descriptor that
describes the throttling status register.
The platform must expose a _PTC object for either all or none of its processors. Notice that if the
_PTC object exists, the specified register is used instead of the P_CNT register specified in the
Processor term. Also notice that if the _PTC object exists and the _CST object does not exist, OSPM
462 April, 2015 Version 6.0