Advanced Configuration and Power Interface Specification

Processor Configuration and Control
performance states including internal CPU core frequency, typical power dissipation, control
register values needed to transition between performance states, and status register values that allow
OSPM to verify performance transition status after any OS-initiated transition change request. The
list is sorted in descending order by typical power dissipation. As a result, the zeroth entry describes
the highest performance state and the ‘nth’ entry describes the lowest performance state.
Arguments:
None
Return Value:
A variable-length Package containing a list of Pstate sub-packages as described below
Return Value Information
Package {
PState [0] // Package – Performance state 0
}
….
PState [n]
// Package – Performance state n
Each Pstate sub-Package contains the elements described below:
Package {
CoreFrequency
Power
Latency
BusMasterLatency
Control
Status
}
// Integer (DWORD)
// Integer (DWORD)
// Integer (DWORD)
// Integer (DWORD)
// Integer (DWORD)
// Integer (DWORD)
Table 8-248 PState Package Values
Element Object Type Description
Core
Frequency
Power
Latency
Bus Master
Latency
Control
Status
Integer
(DWORD)
Integer
(DWORD)
Integer
(DWORD)
Integer
(DWORD)
Integer
(DWORD)
Integer
(DWORD)
Indicates the core CPU operating frequency (in MHz).
Indicates the performance state’s maximum power dissipation (in milliwatts).
Indicates the worst-case latency in microseconds that the CPU is unavailable
during a transition from any performance state to this performance state.
Indicates the worst-case latency in microseconds that Bus Masters are
prevented from accessing memory during a transition from any performance
state to this performance state.
Indicates the value to be written to the Performance Control Register
(PERF_CTRL) in order to initiate a transition to the performance state.
Indicates the value that OSPM will compare to a value read from the
Performance Status Register (PERF_STATUS) to ensure that the transition to
the performance state was successful. OSPM may always place the CPU in
the lowest power state, but additional states are only available when indicated
by the _PPC method.
Version 6.0 471