Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 706

PAL_SET_PSTATE
PAL_SET_PSTATE – Request Processor to Enter Power/Performance
State (263)
To request a processor transition to a given P-state.
Purpose:
Stacked Registers
Calling Conv:
Physical and Virtual
Mode:
Dependent
Buffer:
Arguments:
Argument
index
p_state
force_pstate
Reserved
Returns:
Return Value
status
Reserved
Reserved
Reserved
Status:
Status Value
1
0
-1
-2
-3
-9
PAL_SET_PSTATE is used to request the transition of the processor to the P-state
Description:
specified by the p_state input parameter. The PAL_SET_PSTATE procedure does not wait
for the transition to complete before returning back to the caller. The request may
either be accepted (status = 0) or not accepted (status = 1), depending on hardware
capabilities and implementation-specific event conditions. The presence of a platform
power-cap does not prevent the request from being accepted. (See
"Power/Performance States (P-states)" on page 2:315
accepted, then no transition is performed, and it is up to the caller to make another
PAL_SET_PSTATE procedure call to transition to the desired P-state. When the request
is accepted, the processor will attempt to initiate a transition to the requested
performance state. For SCDD or HIDD logical processors, the procedure will always
succeed in transitioning to the requested performance state. For HCDD logical
processors, the procedure will make a best-case attempt at fulfilling the transition
request, based on the nature of the dependencies that exist between the logical
processors in the domain. In such circumstances, the procedure may initiate no
transition, partial transition or full transition to the requested P-state.
The force_pstate argument may be used for a HCDD when it is necessary to get a
deterministic response for the P-state transition at the expense of compromising the
power/performance of other logical processors in the same domain. If the force_pstate
argument is non-zero, and if the request is accepted, the procedure will initiate the
P-state transition on the logical processor regardless of any dependencies that exist in
the dependency domain at the time the procedure is called. Forcing the P-state does
not change the P-states requested by other logical processors in the dependency
domain, nor the value seen on other logical processors when they do a
PAL_GET_PSTATE with type=0; rather, forcing the P-state effectively suspends hardware
2:458
Description
Index of PAL_SET_PSTATE within the list of PAL procedures.
Unsigned integer denoting the processor P-state being requested.
Unsigned integer denoting whether the P-state change should be forced for the logical
processor.
0
Description
Return status of the PAL_SET_PSTATE procedure.
0
0
0
Description
Call completed without error, but transition request was not accepted
Call completed without error
Unimplemented procedure
Invalid argument
Call completed with error
Call requires PAL memory buffer
Section 11.6.1,
for details.) If the request is not
Volume 2, Part 1: Processor Abstraction Layer