Thermal Specifications and Design Considerations
5.1.3
Intel® Thermal Monitor
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 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. The Intel Thermal Monitor Automatic mode
must be enabled via BIOS for the processor to be operating within
specifications. The automatic mode called Intel Thermal Monitor 1 This mode is
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.
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, however, with
a properly designed and characterized thermal solution the TCC most likely will never
be activated, or only will be activated briefly during the most power intensive
applications.
The TCC may also be activated via On-Demand mode. If bit 4 of the ACPI Intel Thermal
Monitor Control Register is written to a 1, the TCC will be activated immediately,
independent of the processor temperature. When using On-Demand mode to activate
the TCC, the duty cycle of the clock modulation is programmable via bits 3:1 of the
same ACPI Intel Thermal Monitor Control Register. In automatic mode, the duty cycle is
fixed at 50% on, 50% off, however 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 at the same time Automatic mode is enabled, however,
if the system tries to enable the TCC via On-Demand mode at the same time automatic
mode is enabled and a high temperature condition exists, automatic mode will take
precedence.
An external signal, PROCHOT# (processor hot) is asserted when the processor detects
that its temperature is above the thermal trip point. Bus snooping and interrupt
latching are also active while the TCC is active.
Note:
PROCHOT# will not be asserted when the processor is in the Stop Grant, Sleep, Deep
Sleep, and Deeper Sleep low power states (internal clocks stopped), hence the thermal
diode reading must be used as a safeguard to maintain the processor junction
Datasheet
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INTEL [ INTEL ]
