Thermal Specifications

take place. This sequence of temperature checking and Frequency/VID reduction will continue until either the minimum frequency has been reached or the processor temperature has dropped below the TCC activation point.

If the processor temperature remains above the TCC activation point even after the minimum frequency has been reached, then clock modulation (described below) at that minimum frequency will be initiated.

There is no end user software or hardware mechanism to initiate this automated TCC activation behavior.

A small amount of hysteresis has been included to prevent rapid active/inactive transitions of the TCC when the processor temperature is near the TCC activation temperature. Once the temperature has dropped below the trip temperature, and the hysteresis timer has expired, the operating frequency and voltage transition back to the normal system operating point via the intermediate VID/frequency points. Transition of the VID code will occur first, to insure proper operation as the frequency is increased. Refer to Figure 6-7for an illustration of this ordering.

Figure 6-7. Frequency and Voltage Ordering

Temperature

fMAX

f1

f2Frequency

VIDfMAX

VIDf1

VIDf2

VID

 

PROCHOT#

6.2.2.2Clock Modulation

Clock modulation is a second method of thermal control available to the processor. Clock modulation is performed by rapidly turning the clocks off and on at a duty cycle that should reduce power dissipation by about 50% (typically a 30-50% duty cycle). Clocks often will not be off for more than 32 microseconds when the TCC is active. Cycle times are independent of processor frequency. The duty cycle for the TCC, when activated by the Thermal Monitor, is factory configured and cannot be modified.

It is possible for software to initiate clock modulation with configurable duty cycles.

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Thermal/Mechanical Specifications and Design Guidelines