Intel PentiumD 950 HH80553PG0964M User Manual

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periods of TCC activation is expected to be so minor that it would be immeasurable. 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 in some cases may result in a T

C

 that exceeds the specified maximum temperature 

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. Refer to the Intel

Mechanical Design Guidelines for information on designing a thermal solution.

The duty cycle for the TCC, when activated by the Thermal Monitor, is factory 

configured and cannot be modified. The Thermal Monitor does not require any 

additional hardware, software drivers, or interrupt handling routines.

The processor provides an auxiliary mechanism that allows system software to force 

the processor to reduce its power consumption. This mechanism is referred to as “On-

Demand” mode and is distinct from the Thermal Monitor feature. On-Demand mode is 

intended as a means to reduce system level power consumption. Systems using the 

processor must not rely on software usage of this mechanism to limit the processor 

temperature.

If bit 4 of the ACPI P_CNT Control Register (located in the processor 

IA32_THERM_CONTROL MSR) is written to a '1', the processor will immediately reduce 

its power consumption via modulation (starting and stopping) of the internal core clock, 

independent of the processor temperature. When using On-Demand mode, the duty 

cycle of the clock modulation is programmable via bits 3:1 of the same ACPI P_CNT 

Control Register. 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 in conjunction with the Thermal Monitor. If the system tries to enable On-Demand 

mode at the same time the TCC is engaged, the factory configured duty cycle of the 

TCC will override the duty cycle selected by the On-Demand mode. 

An external signal, PROCHOT# (processor hot), is asserted when the processor core 

temperature has reached its maximum operating temperature. If the Thermal Monitor 

is enabled (note that the Thermal Monitor must be enabled for the processor to be 

operating within specification), the TCC will be active when PROCHOT# is asserted. The 

processor can be configured to generate an interrupt upon the assertion or de-

assertion of PROCHOT#. Refer to the Intel Architecture Software Developer's Manuals 

for specific register and programming details.

PROCHOT# can be configured via BIOS as an output or a bi-directional signal. As an 

output, PROCHOT# (Processor Hot) will go active when the processor temperature 

monitoring sensor detects that one or both cores has reached its maximum safe 

operating temperature. This indicates that the processor Thermal Control Circuit (TCC) 

has been activated, if enabled. As an input, assertion of PROCHOT# by the system will 

activate the TCC, if enabled, for both cores. The TCC will remain active until the system 

de-asserts PROCHOT#.

If PROCHOT# is configured as an output only, the FORCEPR# signal can be driven from 

an external source to activate the TCC. This will prevent one core from asserting the 

PROCHOT# signal of the other core and unnecessarily activating the TCC of that core. 

Refer to 

 for details on the FORCEPR# signal.