Intel 4 620 JM80547PG0722MM Data Sheet

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Enhanced HALT is a low power state entered when all logical processors have executed the HALT 
or MWAIT instructions and Enhanced HALT has been enabled via the BIOS. When one of the 
logical processors executes the HALT instruction, that logical processor is halted; however, the 
other processor continues normal operation.

The processor will automatically transition to a lower frequency and voltage operating point before 
entering the Enhanced 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 ratio and then transition to the lower VID.

While in Enhanced HALT state, the processor will process bus snoops.

The processor exits the Enhanced HALT state when a break event occurs. When the processor exits 
the Enhanced HALT state, it will first transition the VID to the original value and then change the 
bus ratio back to the original value.

When the STPCLK# signal is asserted, the Stop-Grant state of the processor is entered 20 bus 
clocks after the response phase of the processor-issued Stop Grant Acknowledge special bus cycle.

Since the GTL+ signals receive power from the FSB, these signals should not be driven (allowing 
the level to return to V

TT

) for minimum power drawn by the termination resistors in this state. In 

addition, all other input signals on the FSB should be driven to the inactive state.

BINIT# will not be serviced while the processor is in Stop-Grant state. The event will be latched 
and can be serviced by software upon exit from the Stop Grant state.

RESET# will cause the processor to immediately initialize itself, but the processor will stay in 
Stop-Grant state. A transition back to the Normal state will occur with the de-assertion of the 
STPCLK# signal.

A transition to the HALT/Grant Snoop state will occur when the processor detects a snoop on the 
FSB.

While in the Stop-Grant State, SMI#, INIT#, BINIT#, and LINT[1:0] will be latched by the 
processor, and only serviced when the processor returns to the Normal State. Only one occurrence 
of each event will be recognized upon return to the Normal state.

While in Stop-Grant state, the processor will process a FSB snoop. 

The Enhanced HALT Snoop State is used in conjunction with the new Enhanced HALT state. If 
Enhanced HALT state is not enabled in the BIOS, the default Snoop State entered will be the 
HALT Snoop State. Refer to the following sections for details on HALT Snoop State, Grant Snoop 
State and Enhanced HALT Snoop State.