Thermal Specifications
6.2
Processor Thermal Features
6.2.1
Thermal Monitor
The Thermal Monitor (TM1) feature helps control the processor temperature by
activating the Thermal Control Circuit (TCC) when the processor silicon reaches its
maximum operating temperature. The TCC reduces processor power consumption as
needed by modulating (starting and stopping) the internal processor core clocks. The
Thermal Monitor (TM1) must be enabled for the processor to be operating within
specifications. The temperature at which Thermal Monitor activates the thermal control
circuit is not user configurable and is not software visible. 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.
When the Thermal Monitor is enabled and a high temperature situation exists (that is,
TCC is active), the clocks will be modulated by alternately turning the clocks off and on
at a duty cycle specific to the processor (typically 30 -50%). Cycle times are processor
speed dependent and will decrease as processor core frequencies increase. A small
amount of hysteresis has been included to prevent rapid active/inactive transitions of
the TCC when the processor temperature is near its maximum operating temperature.
Once the temperature has dropped below the maximum operating temperature, and
the hysteresis timer has expired, the TCC goes inactive and clock modulation ceases.
With a thermal solution designed to meet Thermal Profile A, 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. A
thermal solution that is designed to Thermal Profile B may cause a noticeable
performance loss due to increased TCC activation. Thermal Solutions that exceed
Thermal Profile B will exceed the maximum temperature specification and 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 Dual-Core Intel® Xeon® Processor 5000 Series
Thermal/Mechanical Design Guidelines for information on designing a thermal solution.
The duty cycle for the TCC, when activated by the TM1, is factory configured and
cannot be modified. The TM1 does not require any additional hardware, software
drivers, or interrupt handling routines.
6.2.2
On-Demand Mode
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 utilizing the
Dual-Core Intel Xeon Processor 5000 series must not rely on software usage of this
mechanism to limit the processor temperature. If bit 4 of the
IA32_CLOCK_MODULATION MSR is set 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
IA32_CLOCK_MODULATION MSR. 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; however, if
Dual-Core Intel® Xeon® Processor 5000 Series Datasheet
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