Intel i7-960 AT80601002727AA User Manual

78

Datasheet 

Clock modulation is a second method of thermal control available to the processor. 

Clock modulation is performed by rapidly turning the clocks off and on at a duty cycle 

that should reduce power dissipation by about 50% (typically a 30–50% duty cycle). 

Clocks often will not be off for more than 32 µs when the TCC is active. Cycle times are 

independent of processor frequency. The duty cycle for the TCC, when activated by the 

Thermal Monitor, is factory configured and cannot be modified.

It is possible for software to initiate clock modulation with configurable duty cycles. 

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.

As mentioned above, when the TCC is activated, the processor will sequentially step 
down the ratio multipliers and VIDs in an attempt to reduce the silicon temperature. If 
the temperature continues to increase and exceeds the TCC activation temperature by 
approximately 5 °C before the lowest ratio/VID combination has been reached, then 
the processor will immediately transition to the combined TM1/TM2 condition. The 
processor will remain in this state until the temperature has dropped below the TCC 
activation point. Once below the TCC activation temperature, TM1 will be discontinued 
and TM2 will be exited by stepping up to the appropriate ratio/VID state. 

If TM2 is unable to reduce the processor temperature, then TM1 will be also be 
activated. TM1 and TM2 will then work together to reduce power dissipation and 
temperature. It is expected that only a catastrophic thermal solution failure would 
create a situation where both TM1 and TM2 are active. 

If TM1 and TM2 have both been active for greater than 20 ms and the processor 
temperature has not dropped below the TCC activation point, then the Critical 
Temperature Flag in the IA32_THERM_STATUS MSR will be set. This flag is an indicator 
of a catastrophic thermal solution failure and that the processor cannot reduce its 
temperature. Unless immediate action is taken to resolve the failure, the processor will 
probably reach the Thermtrip temperature (see 

 Thermtrip Signal) within 

a short time. To prevent possible permanent silicon damage, Intel recommends 
removing power from the processor within ½ second of the Critical Temperature Flag 
being set.

An external signal, PROCHOT# (processor hot), is asserted when the processor core 

temperature has exceeded its specification. 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#. 

Although the PROCHOT# signal is an output by default, it may be configured as bi-

directional. When configured in bi-directional mode, it is either an output indicating the 

processor has exceeded its TCC activation temperature or it can be driven from an