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6.2.2.2
Clock Modulation
Clock modulation is performed by alternately turning the clocks off and on at a duty
cycle specific to the processor (factory configured to 37.5% on and 62.5% off for TM1).
The period of the duty cycle is configured to 32 microseconds when the TCC is active.
Cycle times are independent of processor frequency. 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. Clock
modulation is automatically engaged as part of the TCC activation when the
Frequency/SVID targets are at their minimum settings. It may also be initiated by
software at a configurable duty cycle.
6.2.3
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 Adaptive Thermal Monitor feature. On-Demand
mode is intended as a means to reduce system level power consumption. Systems
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 using 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 using bits 3:0
of the same IA32_CLOCK_MODULATION MSR. In On-Demand mode, the duty cycle can
be programmed from 6.25% on / 93.75% off to 93.75% on / 6.25% off in 6.25%
increments. On-Demand mode may be used in conjunction with the Adaptive Thermal
Monitor; however, if the system tries to enable On-Demand mode at the same time the
TCC is engaged, the factory configured duty cycle of the TCC will override the duty
cycle selected by the On-Demand mode.
6.2.4
PROCHOT_N Signal
An external signal, PROCHOT_N (processor hot), is asserted when the processor core
temperature has reached its maximum operating temperature. If Adaptive Thermal
Monitor is enabled (note it must be enabled for the processor to be operating within
specification), the TCC will be active when PROCHOT_N is asserted.
The PROCHOT_N signal is bi-directional in that it can either signal when the processor
(any core) has reached its maximum operating temperature or be driven from an
external source to activate the TCC. The ability to activate the TCC using PROCHOT_N
can provide a means for thermal protection of system components.
As an output, PROCHOT_N will go active when the processor temperature monitoring
sensor detects that one or more cores has reached its maximum safe operating
temperature. This indicates that the processor Thermal Control Circuit (TCC) has been
activated, if enabled. As an input, assertion of PROCHOT_N by the system will activate
the TCC, if enabled, for all cores. TCC activation due to PROCHOT_N assertion by the
system will result in the processor immediately transitioning to the minimum frequency
and corresponding voltage (using Freq/SVID control). Clock modulation is not activated
in this case. The TCC will remain active until the system de-asserts PROCHOT_N.
PROCHOT_N can allow voltage regulator (VR) thermal designs to target maximum
sustained current instead of maximum current. Systems should still provide proper
cooling for the VR, and rely on PROCHOT_N as a backup in case of system cooling
50
Thermal Management Specifications
Thermal/Mechanical Specifications and Design Guide
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