NEC Intel Xeon E5-2420 N8101-571F User Manual

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Intel® Xeon® Processor E5-1600/E5-2600/E5-4600 Product Families

Datasheet Volume One

Clock modulation is performed by alternately turning the clocks off and on at a duty 
cycle specific to the processor (factory configured to 37.5% on and 62.5% off for TM1). 

The period of the duty cycle is configured to 32 microseconds when the TCC is active. 
Cycle times are independent of processor frequency. A small amount of hysteresis has 

been included to prevent rapid active/inactive transitions of the TCC when the 

processor temperature is near its maximum operating temperature. Once the 
temperature has dropped below the maximum operating temperature, and the 

hysteresis timer has expired, the TCC goes inactive and clock modulation ceases. Clock 

modulation is automatically engaged as part of the TCC activation when the Frequency/
SVID targets are at their minimum settings. It may also be initiated by software at a 

configurable duty cycle.

The processor provides an auxiliary mechanism that allows system software to force 
the processor to reduce its power consumption. This mechanism is referred to as “On-

Demand” mode and is distinct from the Adaptive Thermal Monitor feature. On-Demand 

mode is intended as a means to reduce system level power consumption. Systems 
must not rely on software usage of this mechanism to limit the processor temperature. 

If bit 4 of the IA32_CLOCK_MODULATION MSR is set to a ‘1’, the processor will 

immediately reduce its power consumption via modulation (starting and stopping) of 
the internal core clock, independent of the processor temperature. When using On-

Demand mode, the duty cycle of the clock modulation is programmable via bits 3:0 of 

the same IA32_CLOCK_MODULATION MSR. In On-Demand mode, the duty cycle can 
be programmed from 6.25% on / 93.75% off to 93.75% on / 6.25% off in 6.25% 

increments. On-Demand mode may be used in conjunction with the Adaptive Thermal 

Monitor; however, if the system tries to enable On-Demand mode at the same time the 
TCC is engaged, the factory configured duty cycle of the TCC will override the duty 

cycle selected by the On-Demand mode.

An external signal, PROCHOT_N (processor hot), is asserted when the processor core 
temperature has reached its maximum operating temperature. If Adaptive Thermal 

Monitor is enabled (note it must be enabled for the processor to be operating within 

specification), the TCC will be active when PROCHOT_N is asserted. The processor can 
be configured to generate an interrupt upon the assertion or de-assertion of 

PROCHOT_N. 

The PROCHOT_N signal is bi-directional in that it can either signal when the processor 
(any core) has reached its maximum operating temperature or be driven from an 

external source to activate the TCC. The ability to activate the TCC via PROCHOT_N can 

provide a means for thermal protection of system components. 

As an output, PROCHOT_N will go active when the processor temperature monitoring 

sensor detects that one or more cores has reached its maximum safe operating 

temperature. This indicates that the processor Thermal Control Circuit (TCC) has been 
activated, if enabled. As an input, assertion of PROCHOT_N by the system will activate 

the TCC, if enabled, for all cores. TCC activation due to PROCHOT_N assertion by the 
system will result in the processor immediately transitioning to the minimum frequency 

and corresponding voltage (using Freq/SVID control). Clock modulation is not activated 

in this case. The TCC will remain active until the system de-asserts PROCHOT_N.