Intel Pentium D 830 HH80551PG0802MN Data Sheet

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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 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

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 Pentium D 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 Pentium D 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.

For the Pentium D processor, 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.