Intel Core 2 Duo E7300 BX80570E7300 User Manual

Thermal and Mechanical Design Guidelines   

 37 

Regardless of the configuration selected, PROCHOT# will always indicate the thermal 

status of the processor.  

The power reduction mechanism of thermal monitor can also be activated manually 
using an “on-demand” mode. Refer to Section 

4.2.5 for details on this feature. 

For testing purposes, the thermal control circuit may also be activated by setting bits 

in the ACPI MSRs. The MSRs may be set based on a particular system event (e.g., an 

interrupt generated after a system event), or may be set at any time through the 

operating system or custom driver control thus forcing the thermal control circuit on. 

This is referred to as “on-demand” mode. Activating the thermal control circuit may be 

useful for thermal solution investigations or for performance implication studies. When 

using the MSRs to activate the on-demand clock modulation feature, the duty cycle is 

configurable in steps of 12.5%, from 12.5% to 87.5%.  

For any duty cycle, the maximum time period the clocks are disabled is ~3 s. This 

time period is frequency dependent, and decreases as frequency increases. To achieve 

different duty cycles, the length of time that the clocks are disabled remains constant, 

and the time period that the clocks are enabled is adjusted to achieve the desired 

ratio. For example, if the clock disable period is 3 µs, and a duty cycle of ¼ (25%) is 

selected, the clock on time would be reduced to approximately 1 s [on time (1 s)  
total cycle time (3 + 1) s = ¼ duty cycle]. Similarly, for a duty cycle of 7/8 (87.5%), 
the clock on time would be extended to 21 s [21  (21 + 3) = 7/8 duty cycle]. 

In a high temperature situation, if the thermal control circuit and ACPI MSRs 

(automatic and on-demand modes) are used simultaneously, the fixed duty cycle 

determined by automatic mode would take precedence.  

Note:  On-demand mode can not activate the power reduction mechanism of Thermal 

Monitor 2 

Intel requires the Thermal Monitor and Thermal Control Circuit to be enabled for all 

processors. The thermal control circuit is intended to protect against short term 

thermal excursions that exceed the capability of a well designed processor thermal 

solution. Thermal Monitor should not be relied upon to compensate for a thermal 

solution that does not meet the thermal profile up to the thermal design power (TDP). 

Each application program has its own unique power profile, although the profile has 

some variability due to loop decisions, I/O activity and interrupts. In general, compute 

intensive applications with a high cache hit rate dissipate more processor power than 

applications that are I/O intensive or have low cache hit rates. 

The processor TDP is based on measurements of processor power consumption while 

running various high power applications. This data is used to determine those 

applications that are interesting from a power perspective. These applications are then 

evaluated in a controlled thermal environment to determine their sensitivity to 

activation of the thermal control circuit. This data is used to derive the TDP targets 

published in the processor datasheet.