Features
The Enhanced HALT state must be enabled by way of the BIOS for the processor to
remain within its specifications. The Enhanced HALT state requires support for dynamic
VID transitions in the platform.
Figure 7-1. Stop Clock State Machine
HALT or MWAIT Instruction and
HALT Bus Cycle Generated
Enhanced HALT or HALT State
BCLK running
Normal State
INIT#, BINIT#, INTR, NMI, SMI#,
RESET#, FSB interrupts
Normal execution
Snoops and interrupts allowed
Snoop
Event
Occurs Serviced
Snoop
Event
STPCLK#
Asserted
STPCLK#
De-asserted
Enhanced HALT Snoop or HALT
Snoop State
BCLK running
Service snoops to caches
Snoop Event Occurs
Snoop Event Serviced
Stop Grant State
Stop Grant Snoop State
BCLK running
BCLK running
Snoops and interrupts allowed
Service snoops to caches
7.2.3
Stop-Grant State
When the STPCLK# pin 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. Once the STPCLK# pin has been asserted, it may only be deasserted
once the processor is in the Stop Grant state. For the Dual-Core Intel Xeon Processor
5000 series, all logical processor cores will enter the Stop-Grant state once the
STPCLK# pin is asserted. Additionally, all logical cores must be in the Stop Grant state
before the deassertion of STPCLK#.
Since the AGTL+ signal pins receive power from the front side bus, these pins should
not be driven (allowing the level to return to VTT) for minimum power drawn by the
termination resistors in this state. In addition, all other input pins on the front side bus
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.
Dual-Core Intel® Xeon® Processor 5000 Series Datasheet
85
INTEL [ INTEL ]
