Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
Processor performance control objects include the ‘_PCT’ package, ‘_PSS’ package, and the ‘_PPC’
method as detailed below.
8.4.6.1 _PCT (Performance Control)
This optional object declares an interface that allows OSPM to transition the processor into a
performance state. OSPM performs processor performance transitions by writing the performance
state–specific control value to a Performance Control Register (PERF_CTRL).
OSPM may select a processor performance state as indicated by the performance state value
returned by the _PPC method, or any lower power (higher numbered) state. The control value to
write is contained in the corresponding _PSS entry’s “Control” field.
Success or failure of the processor performance transition is determined by reading a Performance
Status Register (PERF_STATUS) to determine the processor’s current performance state. If the
transition was successful, the value read from PERF_STATUS will match the “Status” field in the
_PSS entry that corresponds to the desired processor performance state.
Arguments:
None
Return Value:
A Package as described below
Return Value Information
Package
{
ControlRegister
StatusRegister
}
// Buffer (Resource Descriptor)
// Buffer (Resource Descriptor)
Table 8-247 PCT Package Values
Element Object Type Description
Control
Register
Status
Register
Buffer
Buffer
Contains a Resource Descriptor with a single Register() descriptor that
describes the performance control register.
Contains a Resource Descriptor with a single Register() descriptor that
describes the performance status register.
Example
Name (_PCT, Package()
{
ResourceTemplate(){Perf_Ctrl_Register},
ResourceTemplate(){Perf_Status_Register}
}) // End of _PCT
//Generic Register Descriptor
//Generic Register Descriptor
8.4.6.2 _PSS (Performance Supported States)
This optional object indicates to OSPM the number of supported processor performance states that
any given system can support. This object evaluates to a packaged list of information about available
470 April, 2015 Version 6.0