Intel Pentium 4 Processor on 90 nm Process Thermal and Mechanical Design Guidelines

Thermal Requirements
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28 Intel
®
Pentium
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4 on 90 nm Process Thermal Design Guide
3.4.6 System Considerations
The Thermal Monitor feature may be used in a variety of ways, depending on the system design
requirements and capabilities.
Note: Intel requires the Thermal Monitor and Thermal Control Circuit to be enabled for all
Pentium 4 processor on 90 nm process -based systems. The thermal control circuit is intended
to protect against short term thermal excursions that exceed the capability of a well designed
processor thermal solution. Thermal Monitor should not be relied upon to compensate for a
thermal solution that does not meet the thermal design power (TDP) or the thermal profile.
Each application program has its own unique power profile, although the profile has some
variability due to loop decisions, I/O activity and interrupts. In general, compute intensive
applications with a high cache hit rate dissipate more processor power than applications that are
I/O intensive or have low cache hit rates.
The processor thermal design power (TDP) is based on measurements of processor power
consumption while running various high-power applications. This data is used to determine those
applications that are interesting from a power perspective. These applications are then evaluated
in a controlled thermal environment to determine their sensitivity to activation of the thermal
control circuit. This data is used to derive the TDP targets published in the processor datasheet.
A system designed to meet the thermal profile at the TDP and T
C-MAX
values targets published in
the processor datasheet greatly reduces the probability of real applications causing the thermal
control circuit to activate under normal operating conditions. Systems that do not meet these
specifications could be subject to more frequent activation of the thermal control circuit
depending upon ambient air temperature and application power profile. Moreover, if a system is
significantly under designed, there is a risk that the Thermal Monitor feature will not be capable
of maintaining a safe operating temperature and the processor could shutdown and signal
THERMTRIP#.
For information regarding THERMTRIP#, refer to Section 3.4.8.2 and to the Intel
®
Pentium
®
4
Processor on 90 nm Process Datasheet.
3.4.7 Operating System and Application Software
Considerations
The Thermal Monitor feature and its thermal control circuit work seamlessly with ACPI
compliant operating systems. The Thermal Monitor feature is transparent to application software
since the processor bus snooping, ACPI timer, and interrupts are active at all times.
Activation of the thermal control circuit during a non-ACPI aware operating system boot process
may result in incorrect calibration of operating system software timing loops. The BIOS must
disable the thermal control circuit prior to boot and then the operating system or BIOS must
enable the thermal control circuit after the operating system boot process completes.
Intel has worked with the major operating system vendors to ensure support for non-execution
based operating system calibration loops and ACPI support for the Thermal Monitor feature.