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Figure 21.
Processor Low Power State Machine
Normal State
- Normal Execution
STPCLK#
Asserted
Stop Grant State
- BCLK running
- Snoops and interrupts
allowed
6.2.1
Normal State
This is the normal operating state for the processor.
6.2.2
HALT and Extended HALT Powerdown States
The processor supports the HALT or Extended HALT powerdown state. The Extended
HALT Powerdown must be enabled via the BIOS for the processor to remain within its
specification.
The Extended HALT state is a lower power state as compared to the Stop Grant State.
If Extended HALT is not enabled, the default Powerdown state entered will be HALT.
Refer to the sections below for details about the HALT and Extended HALT states.
6.2.2.1
HALT Powerdown State
HALT is a low power state entered when all the processor cores have executed the HALT
or MWAIT instructions. When one of the processor cores executes the HALT instruction,
that processor core is halted, however, the other processor continues normal operation.
The processor will transition to the Normal state upon the occurrence of SMI#, INIT#,
or LINT[1:0] (NMI, INTR). RESET# will cause the processor to immediately initialize
itself.
The return from a System Management Interrupt (SMI) handler can be to either
Normal Mode or the HALT Power Down state. See the Intel Architecture Software
Developer's Manual, Volume III: System Programmer's Guide for more information.
84
HALT or MWAIT Instruction and
HALT Bus Cycle Generated
INIT#, BINIT#, INTR, NMI, SMI#,
RESET#, FSB interrupts
STPCLK#
STPCLK#
De-asserted
Asserted
Snoop Event Occurs
Snoop Event Serviced
Extended HALT or HALT
State
- BCLK running
- Snoops and interrupts
allowed
Snoop
Event
Occurs
STPCLK#
De-asserted
Extended HALT Snoop or
HALT Snoop State
- BCLK running
- Service Snoops to cahces
Stop Grant Snoop State
- BCLK running
- Service Snoops to cahces
Features
Snoop
Event
Serviced
SleepStateFigure
Datasheet
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