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Thermal Specifications and Design Considerations
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5.1.3
Intel
The Intel Thermal Monitor helps control the processor temperature by activating the TCC when the
processor silicon reaches its maximum operating temperature. The temperature at which Intel
Thermal Monitor activates the thermal control circuit is not user configurable and is not software
visible. Bus traffic is snooped in the normal manner, and interrupt requests are latched (and
serviced during the time that the clocks are on) while the TCC is active.
With a properly designed and characterized thermal solution, it is anticipated that the TCC would
only be activated for very short periods of time when running the most power intensive
applications. The processor performance impact due to these brief periods of TCC activation is
expected to be so minor that it would not be detectable. An under-designed thermal solution that is
not able to prevent excessive activation of the TCC in the anticipated ambient environment may
cause a noticeable performance loss, and may affect the long-term reliability of the processor. In
addition, a thermal solution that is significantly under designed may not be capable of cooling the
processor even when the TCC is active continuously.
The Intel Thermal Monitor controls the processor temperature by modulating (starting and
stopping) the processor core clocks or by initiating an Enhanced Intel SpeedStep technology
transition when the processor silicon reaches its maximum operating temperature. The Intel
Thermal Monitor uses two modes to activate the TCC: Automatic mode and On-Demand mode. If
both modes are activated, Automatic mode takes precedence.
Caution: The Intel Thermal Monitor Automatic Mode mst be enabled via BIOS for the processor to be
operating within specifications.
There are two automatic modes called Intel Thermal Monitor 1 and Intel Thermal Monitor 2. These
modes are selected by writing values to the Model Specific registers (MSRs) of the processor. After
Automatic mode is enabled, the TCC will activate only when the internal die temperature reaches
the maximum allowed value for operation.
Likewise, when Intel Thermal Monitor 2 is enabled, and a high temperature situation exists, the
processor will perform an Enhanced Intel SpeedStep technology transition to a lower operating
point. When the processor temperature drops below the critical level, the processor will make an
Enhanced Intel SpeedStep technology transition to the last requested operating point. Intel Thermal
Monitor 2 is the recommended mode on the Intel
If a processor load based Enhanced Intel SpeedStep technology transition (through MSR write) is
initiated when an Intel Thermal Monitor 2 period is active, there are two possible results:
1.If the processor load based Enhanced Intel SpeedStep technology transition target frequency is
higher than the Intel Thermal Monitor 2 transition based target frequency, the processor load-
based transition will be deferred until the Intel Thermal Monitor 2 event has been completed.
2.If the processor load-based Enhanced Intel SpeedStep technology transition target frequency is
lower than the Intel Thermal Monitor 2 transition based target frequency, the processor will
transition to the processor load-based Enhanced Intel SpeedStep technology target frequency
point.
When Intel Thermal Monitor 1 is enabled, and a high temperature situation exists, the clocks will
be modulated by alternately turning the clocks off and on at a 50% duty cycle. Cycle times are
processor speed dependent and will decrease linearly as processor core frequencies increase. Once
the temperature has returned to a non-critical level, modulation ceases and TCC goes inactive. A
small amount of hysteresis has been included to prevent rapid active/inactive transitions of the
TCC when the processor temperature is near the trip point. The duty cycle is factory configured
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Thermal Monitor
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Pentium
M processors.
Datasheet
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