Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
When Autonomous Selection is enabled, OSPM limits the processor's performance selection by
writing appropriate constraining values to the Minimum and Maximum Performance registers.
Setting Minimum and Maximum to the same value effectively disables Autonomous selection.
Note: When processors are within the same dependency domain, Maximum performance may only be
actually limited when allowed by hardware coordination.
8.4.7.1.2.1 Maximum Performance Register
Optional
Register Location: PCC or Functional Fixed Hardware
Attribute:
Read/Write
Size:
8-32 bits
Maximum Performance Register conveys the maximum performance level at which the platform
may run. Maximum performance may be set to any performance value in the range [Lowest
Performance, Highest Performance], inclusive.
The value written to the Maximum Performance Register conveys a request to limit maximum
performance for the purpose of energy efficiency or thermal control and the platform limits its
performance accordingly as possible. However, the platform may exceed the requested limit in the
event it is necessitated by internal package optimization. For Example, hardware coordination
among multiple logical processors with interdependencies.
OSPM's use of this register to limit performance for the purpose of thermal control must
comprehend multiple logical processors with interdependencies. i.e. the same value must be written
to all processors within a domain to achieve the desired result.
The platform must implement either both the Minimum Performance and Maximum Performance
registers or neither register. If neither register is implemented and Autonomous Selection is disabled,
the platform must always deliver the desired performance.
8.4.7.1.2.2 Minimum Performance Register
Optional
Register Location: PCC or Functional Fixed Hardware
Attribute:
Read/Write
Size:
8-32 bits
The Minimum Performance Register allows OSPM to convey the minimum performance level at
which the platform may run. Minimum performance may be set to any performance value in the
range [Lowest Performance, Highest Performance], inclusive but must be set to a value that is less
than or equal to that specified by the Maximum Performance Register.
In the presence of a physical constraint, for example a thermal excursion, the platform may not be
able to successfully maintain minimum performance in accordance with that set via the Minimum
Performance Register. In this case, the platform issues a Notify event of type 0x84 to the processor
device object and sets the Minimum_Excursion bit within the Performance Limited Register.
The platform must implement either both the Minimum Performance and Maximum Performance
registers or neither register. If neither register is implemented and Autonomous Selection is disabled,
the platform must always deliver the desired performance.
484 April, 2015 Version 6.0