Intel 220 LE80557RE009512 Data Sheet

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Datasheet

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 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 through BIOS for the 

processor to be operating within specifications. 

The processor supports an automatic mode called Intel Thermal Monitor 1 (TM1). This 

mode is enabled 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. 

During high temperature situations, TM1 will modulate the clocks 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. 

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.