Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
Return Value:
A variable-length Package containing a list of C-state information Packages as described below
Return Value Information
_CST returns a variable-length Package that contains the following elements:
Count
An Integer that contains the number of CState sub-packages that follow
CStates[] A list of Count CState sub-packages
Package {
Count
CStates[0]
….
CStates[Count-1]
}
// Integer
// Package
// Package
Each fixed-length Cstate sub-Package contains the elements described below:
Package {
Register
Type
Latency
Power
}
// Buffer (Resource Descriptor)
// Integer (BYTE)
// Integer (WORD)
// Integer (DWORD)
Table 8-236 Cstate Package Values
Element Object Type Description
Register Buffer Contains a Resource Descriptor with a single Register() descriptor that
describes the register that OSPM must read to place the processor in the
corresponding C state.
Type Integer
(BYTE)
The C State type (1=C1, 2=C2, 3=C3). This field conveys the semantics to be
used by OSPM when entering/exiting the C state. Zero is not a valid value.
Latency
Power
Integer
(WORD)
Integer
(DWORD)
The worst-case latency to enter and exit the C State (in microseconds). There
are no latency restrictions.
The average power consumption of the processor when in the corresponding
C State (in milliwatts).
The platform must expose a _CST object for either all or none of its processors. If the _CST object
exists, OSPM uses the C state information specified in the _CST object in lieu of P_LVL2 and
P_LVL3 registers defined in P_BLK and the P_LVLx_LAT values defined in the FADT. Also
notice that if the _CST object exists and the _PTC object does not exist, OSPM will use the
Processor Control Register defined in P_BLK and the C_State_Register registers in the _CST
object.
The platform may change the number or type of C States available for OSPM use dynamically by
issuing a Notify event on the processor object with a notification value of 0x81. This will cause
OSPM to re-evaluate any _CST object residing under the processor object notified. For example, the
430 April, 2015 Version 6.0