Intel Xeon E5540 P4X-DPE5540-253-8M586 User Manual

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Intel

®

 Xeon

®

 Processor 5500 Series Datasheet, Volume 1

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). 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/VID 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 
utilizing the Intel Xeon processor 5500 series 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 3:1 of the same 
IA32_CLOCK_MODULATION MSR. In On-Demand mode, the duty cycle can be 
programmed from 12.5% on/ 87.5% off to 87.5% on/12.5% off in 12.5% 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# (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# is asserted. The processor can 

be configured to generate an interrupt upon the assertion or de-assertion of 

PROCHOT#.

The PROCHOT# 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# can 

provide a means for thermal protection of system components. 

As an output, PROCHOT# 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# by the system will activate 
the TCC, if enabled, for all cores. TCC activation due to PROCHOT# assertion by the 
system will result in the processor immediately transitioning to the minimum frequency 
and corresponding voltage (using Freq/VID control). Clock modulation is not activated 
in this case. The TCC will remain active until the system de-asserts PROCHOT#.