Intel Xeon Processor with 800 MHz System Bus Thermal/Mechanical Design Guide

Intel® Xeon™ Processor with 800 MHz System Bus Thermal/Mechanical Design Guidelines 77
Processor Thermal Management Logic and Thermal Monitor Features
Note: Intel requires the TCC to be enabled for all Intel Xeon Processor with 800 MHz System Bus
based systems. At a minimum, the TCC provides an added level of protection against processor
thermal solution failure.
A system designed to meet the TDP and T
CASE
targets published in the processor Intel® Xeon™
Processor with 800 MHz System Bus at 2.80 GHz and 3.60 GHz Datasheet greatly reduces the
probability of real applications causing the TCC to activate under normal operating conditions.
Systems that do not meet these specifications could be subject to more frequent activation of the
TCC 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 Appendix F.1.7.2 and to the Intel® Xeon™
Processor with 800 MHz System Bus at 2.80 GHz and 3.60 GHz Datasheet.
F.1.6 Operating System and Application Software Considerations
The Thermal Monitor feature and its TCC work seamlessly with ACPI compliant operating
systems and those utilizing hardware based timing routines. 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 TCC during a non-ACPI aware operating system boot process may result in
incorrect calibration of operating system software timing loops. This is also the case with
operating systems that utilize execution based timing routines. The BIOS must disable the TCC
prior to boot and then the operating system or BIOS must enable the TCC 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.
F.1.7 Legacy Thermal Management Capabilities
In addition to Thermal Monitor, the Intel Xeon Processor with 800 MHz System Bus supports the
same thermal management features originally introduced with the Intel
®
Pentium
®
III Xeon
processor. These features include the on-die thermal diode and THERMTRIP# signal for
indicating catastrophic thermal failure.
F.1.7.1 On-Die Thermal Diode
There are two independent thermal diodes in the Intel Xeon Processor with 800 MHz System Bus.
One is the on-die thermal diode and the other is in the temperature sensor used for the Thermal
Monitor and for THERMTRIP#. The Thermal Monitor’s temperature sensor and the on-die
thermal diode are independent and isolated devices with no direct correlation to one another.
Circuit constraints and performance requirements prevent the Thermal Monitor’s temperature
sensor and the on-die thermal diode from being located at the same place on the silicon. The
temperature distribution across the die may result in significant temperature differences between
the on-die thermal diode and the Thermal Monitor’s temperature sensor. This temperature
variability across the die is highly dependent on the application being run. As a result, it is not
possible to predict the activation of the TCC by monitoring the on-die thermal diode.