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Datasheet

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

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