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6.2.4.1
HALT Snoop State, Stop Grant Snoop State
The processor will respond to snoop transactions on the FSB while in Stop-Grant state
or in HALT Power Down state. During a snoop transaction, the processor enters the
HALT Snoop State:Stop Grant Snoop state. The processor will stay in this state until the
snoop on the FSB has been serviced (whether by the processor or another agent on the
FSB). After the snoop is serviced, the processor will return to the Stop Grant state or
HALT Power Down state, as appropriate.
6.2.4.2
Extended HALT Snoop State
The Extended HALT Snoop State is the default Snoop State when the Extended HALT
state is enabled via the BIOS. The processor will remain in the lower bus ratio and VID
operating point of the Extended HALT state.
While in the Extended HALT Snoop State, snoops are handled the same way as in the
HALT Snoop State. After the snoop is serviced the processor will return to the Extended
HALT state.
6.2.5
Enhanced Intel SpeedStep
The processor supports Enhanced Intel SpeedStep Technology. This technology enables
the processor to switch between frequency and voltage points, which may result in
platform power savings. In order to support this technology, the system must support
dynamic VID transitions. Switching between voltage/frequency states is software
controlled.
Enhanced Intel SpeedStep Technology is a technology that creates processor
performance states (P states). P states are power consumption and capability states
within the Normal state as shown in
enables real-time dynamic switching between frequency and voltage points. It alters
the performance of the processor by changing the bus to core frequency ratio and
voltage. This allows the processor to run at different core frequencies and voltages to
best serve the performance and power requirements of the processor and system. Note
that the front side bus is not altered; only the internal core frequency is changed. In
order to run at reduced power consumption, the voltage is altered in step with the bus
ratio.
The following are key features of Enhanced Intel SpeedStep Technology:
• Voltage/Frequency selection is software controlled by writing to processor MSR's
(Model Specific Registers), thus eliminating chipset dependency.
- If the target frequency is higher than the current frequency, Vcc is incremented in
steps (+12.5 mV) by placing a new value on the VID signals after which the
processor shifts to the new frequency. Note that the top frequency for the
processor can not be exceeded.
- If the target frequency is lower than the current frequency, the processor shifts to
the new frequency and Vcc is then decremented in steps (-12.5 mV) by changing
the target VID through the VID signals.
6.2.6
Processor Power Status Indicator (PSI) Signal
The processor incorporates the PSI# signal that is asserted when the processor is in a
reduced power consumption state. PSI# can be used to improve efficiency of the
voltage regulator, resulting in platform power savings. For details, refer to the
compatible chipset Platform Design Guide and Voltage Regulator-Down (VRD) 11.1
Processor Power Delivery Design Guidelines.
PSI# may be asserted only when the processor is in the Deeper Sleep state.
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Technology
Figure
6-1. Enhanced Intel SpeedStep Technology
Features
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