Normal State; Halt Or Extended Halt State - Intel 5148LV - Xeon Dual Core Active H Datasheet

7.2.1

Normal State

This is the normal operating state for the processor.
7.2.2

HALT or Extended HALT State

The Extended HALT state (C1E) is enabled via the BIOS. The Extended HALT state
must be enabled for the processor to remain within its specifications. The
Extended HALT state requires support for dynamic VID transitions in the platform.
7.2.2.1 HALT State
HALT is a low power state entered when the processor have executed the HALT or
MWAIT instruction. When one of the processor cores execute the HALT or MWAIT
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#, BINIT#, INIT#, LINT[1:0] (NMI, INTR), or an interrupt delivered over the
front side bus. 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 state. See the IA-32 Intel
Developer's Manual, Volume III: System Programming Guide for more information.
The system can generate a STPCLK# while the processor is in the HALT state. When the
system deasserts STPCLK#, the processor will return execution to the HALT state.
While in HALT state, the processor will process front side bus snoops and interrupts.
7.2.2.2 Extended HALT State
Extended HALT state is a low power state entered when both processor cores have
executed the HALT or MWAIT instructions and Extended HALT state has been enabled
via the BIOS. When one of the processor cores executes the HALT instruction, that
processor core is halted; however, the other processor core continues normal
operation. The Extended HALT state is a lower power state than the HALT state or Stop
Grant state. The Extended HALT state must be enabled for the processor to remain
within its specifications.
The processor will automatically transition to a lower core frequency and voltage
operating point before entering the Extended HALT state. Note that the processor FSB
frequency is not altered; only the internal core frequency is changed. When entering
the low power state, the processor will first switch to the lower bus to core frequency
ratio and then transition to the lower voltage (VID).
While in the Extended HALT state, the processor will process bus snoops.
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