Thermal Specifications and Design Considerations
5.2
Intel® Thermal Monitor
The Intel Thermal Monitor helps control the processor temperature by activating the
TCC (Thermal Control Circuit) when the processor silicon reaches its maximum
operating temperature. The temperature at which the Intel Thermal Monitor activates
the TCC is not user configurable. 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 minor and hence not 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.
There are two automatic modes called Intel Thermal Monitor-1 and Intel Thermal
Monitor-2. These modes are selected by writing values to the 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.
The Intel Thermal Monitor automatic mode must be enabled through BIOS for the
processor to be operating within specifications. Intel recommends Intel Thermal
Monitor-1 and Intel Thermal Monitor-2 be enabled on the processor.
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 and
cannot be modified. Also, automatic mode does not require any additional hardware,
software drivers, or interrupt handling routines. Processor performance will be
decreased by the same amount as the duty cycle when the TCC is active.
When Intel Thermal Monitor-2 is enabled and a high temperature situation exists, the
processor will perform an Enhanced Intel SpeedStep Technology transition to the LFM.
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. The processor also supports Enhanced Multi Threaded Thermal
Monitoring (EMTTM). EMTTM is a processor feature that enhances Intel Thermal
Monitor-2 with a processor throttling algorithm known as Adaptive Intel Thermal
Monitor-2. Adaptive Intel Thermal Monitor-2 transitions to intermediate operating
points, rather than directly to the LFM, once the processor has reached its thermal
Datasheet
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