Data Sheet

Datasheet, Volume 1 of 2 75
Power Management
This feature is disabled by default. BIOS should enable it in the
PMG_CST_CONFIG_CONTROL register. The auto-demotion policy is also configured by
this register.
4.2.5 Package C-States
The processor supports C0, C2, C3, C6, C7, C8, C9, and C10 package states. The
following is a summary of the general rules for package C-state entry. These apply to
all package C-states, unless specified otherwise:
• A package C-state request is determined by the lowest numerical processor IA core
C-state amongst all processor IA cores.
• A package C-state is automatically resolved by the processor depending on the
processor IA core idle power states and the status of the platform components.
— Each processor IA core can be at a lower idle power state than the package if
the platform does not grant the processor permission to enter a requested
package C-state.
— The platform may allow additional power savings to be realized in the
processor.
— For package C-states, the processor is not required to enter C0 before entering
any other C-state.
— Entry into a package C-state may be subject to auto-demotion – that is, the
processor may keep the package in a deeper package C-state then requested
by the operating system if the processor determines, using heuristics, that the
deeper C-state results in better power/performance.
The processor exits a package C-state when a break event is detected. Depending on
the type of break event, the processor does the following:
• If a processor IA core break event is received, the target processor IA core is
activated and the break event message is forwarded to the target processor IA
core.
— If the break event is not masked, the target processor IA core enters the
processor IA core C0 state and the processor enters package C0.
— If the break event is masked, the processor attempts to re-enter its previous
package state.
• If the break event was due to a memory access or snoop request,
— But the platform did not request to keep the processor in a higher package C-
state, the package returns to its previous C-state.
— And the platform requests a higher power C-state, the memory access or snoop
request is serviced and the package remains in the higher power C-state.