Data Sheet

Datasheet, Volume 1 of 2 71
Power Management
4.2 Processor IA Core Power Management
While executing code, Enhanced Intel
®
SpeedStep
®
Technology and Intel Speed
Shift
®
Technology optimizes the processor’s IA core frequency and voltage based on
workload. Each frequency and voltage operating point is defined by ACPI as a P-state.
When the processor is not executing code, it is idle. A low-power idle state is defined by
ACPI as a C-state. In general, deeper power C-states have longer entry and exit
latencies.
4.2.1 OS/HW Controlled P-states
4.2.1.1 Enhanced Intel
®
SpeedStep
®
Technology
Enhanced Intel
®
SpeedStep
®
Technology enables OS to control and select P-state. The
following are the key features of Enhanced Intel
®
SpeedStep
®
Technology:
Multiple frequency and voltage points for optimal performance and power
efficiency. These operating points are known as P-states.
Frequency selection is software controlled by writing to processor MSRs. The
voltage is optimized based on the selected frequency and the number of active
processor IA cores.
Once the voltage is established, the PLL locks on to the target frequency.
All active processor IA cores share the same frequency and voltage. In a multi-
core processor, the highest frequency P-state requested among all active IA
cores is selected.
Software-requested transitions are accepted at any time. If a previous
transition is in progress, the new transition is deferred until the previous
transition is completed.
The processor controls voltage ramp rates internally to ensure glitch-free
transitions.
Because there is low transition latency between P-states, a significant number of
transitions per-second are possible.
Table 4-6. G, S, and C Interface State Combinations
Global
(G)
State
Sleep (S)
State
Processor
Package (C)
State
Processor
State
System Clocks Description
G0 S0 C0 Full On On Full On
G0 S0 C1/C1E Auto-Halt On Auto-Halt
G0 S0 C3 Deep Sleep On Deep Sleep
G0 S0 C6/C7
Deep Power
Down
On Deep Power Down
G0 S0 C8/C9/C10 Off On Deeper Power Down
G1 S3 Power off Off Off, except RTC Suspend to RAM
G1 S4 Power off Off Off, except RTC Suspend to Disk
G2 S5 Power off Off Off, except RTC Soft Off
G3 N/A Power off Off Power off Hard off