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Thermal Specifications

98 Intel® Xeon® Processor 7400 Series Datasheet

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 Intel 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 the Intel® Xeon® Processor 7400 Series

Thermal Profiles, 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. 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® Xeon® Processor 7400 Series

Thermal Mechanical Design Guide or information on designing a thermal solution.

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

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

additional hardware, software drivers, or interrupt handling routines.

6.2.3 Intel Thermal Monitor 2

The Intel® Xeon® Processor 7400 Series adds supports for an Enhanced Thermal

Monitor capability known as Intel Thermal Monitor 2 (TM2). This mechanism provides

an efficient means for limiting the processor temperature by reducing the power

consumption within the processor. The Intel Thermal Monitor or Enhanced Thermal

Monitor must be enabled for the processor to be operating within specifications. TM2

requires support for dynamic VID transitions in the platform.

Note: Not all Intel® Xeon® Processor 7400 Series are capable of supporting TM2. More detail

on which processor frequencies will support TM2 will be provided in future releases of

the Intel® Xeon® Processor 7400 Series Specification Update when available.

When Intel Thermal Monitor 2 is enabled, and a high temperature situation is detected,

the Thermal Control Circuit (TCC) will be activated for all processor cores. The TCC

causes the processor to adjust its operating frequency (via the bus multiplier) and

input voltage (via the VID signals). This combination of reduced frequency and VID

results in a reduction to the processor power consumption.

A processor enabled for Intel Thermal Monitor 2 includes two operating points, each

consisting of a specific operating frequency and voltage, which is identical for both

processor dies. The first operating point represents the normal operating condition for

the processor. Under this condition, the core-frequency-to-system-bus multiplier

utilized by the processor is that contained in the CLOCK_FLEX_MAX MSR and the VID

that is specified in Table 2-3.

The second operating point consists of both a lower operating frequency and voltage.

The lowest operating frequency is determined by the lowest supported bus ratio (1/8

for the Intel® Xeon® Processor 7400 Series). When the TCC is activated, the processor

automatically transitions to the new frequency. This transition occurs rapidly, on the

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