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Power Management
4.2.1
Enhanced Intel
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 cores.
— If the target frequency is higher than the current frequency, V
in steps to an optimized voltage. This voltage is signaled by the VID[7:0] pins
to the voltage regulator. Once the voltage is established, the PLL locks on to the
target frequency.
— If the target frequency is lower than the current frequency, the PLL locks to the
target frequency, then transitions to a lower voltage by signaling the target
voltage on the VID[7:0] pins.
— All active processor cores share the same frequency and voltage. In a multi-
core processor, the highest frequency P-state requested amongst all active
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.
4.2.2
Low-Power Idle States
When the processor is idle, low-power idle states (C-states) are used to save power.
More power savings actions are taken for numerically higher C-states. However, higher
C-states have longer exit and entry latencies. Resolution of C-states occur at the
thread, processor core, and processor package level. Thread level C-states are
available if Intel Hyper-Threading Technology is enabled.
Figure 4-1.
Idle Power Management Breakdown of the Processor Cores
Datasheet, Volume 1
®
®
SpeedStep
Technology
Thread 0
Thread 1
Core 0 State
Processor Package State
Thread 0
Thread 1
Core 1 State
is ramped up
CC
37
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