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the Stop Grant SBC on the bus before allowing the processor to be transitioned into one
of the lower processor power states. Refer to the applicable chipset specification and
the Conroe and Woodcrest Processor Family BIOS Writer's Guide for more information.
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. Refer to the Conroe and
Woodcrest Processor Family BIOS Writer's Guide. 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 has 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 Intel® 64 and IA-32 Intel® Architecture
Software 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 all four 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 cores continue 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. The processor
exits the Extended HALT state when a break event occurs. When the processor exits
the Extended HALT state, it will first transition the VID to the original value and then
change the bus to core frequency ratio back to the original value.
106
Quad-Core Intel® Xeon® Processor 5300 Series Datasheet
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