User Guide

Thermal Management
86 Datasheet, Volume 1 of 2
5.1.5.1.2 Frequency / Voltage Control
Upon Adaptive Thermal Monitor activation, the processor attempts to dynamically
reduce processor temperature by lowering the frequency and voltage operating point.
The operating points are automatically calculated by the processor IA core itself and do
not require the BIOS to program them as with previous generations of Intel processors.
The processor IA core will scale the operating points such that:
• The voltage will be optimized according to the temperature, the processor IA core
bus ratio and number of processor IA cores in deep C-states.
• The processor IA core power and temperature are reduced while minimizing
performance degradation.
Once the temperature has dropped below the trigger temperature, the operating
frequency and voltage will transition back to the normal system operating point.
Once a target frequency/bus ratio is resolved, the processor IA core will transition to
the new target automatically.
• On an upward operating point transition the voltage transition precedes the
frequency transition.
• On a downward transition the frequency transition precedes the voltage transition.
• The processor continues to execute instructions. However, the processor will halt
instruction execution for frequency transitions.
If a processor load-based Enhanced Intel SpeedStep Technology/P-state transition
(through MSR write) is initiated while the Adaptive Thermal Monitor is active, there are
two possible outcomes:
• If the P-state target frequency is higher than the processor IA core optimized
target frequency, the P-state transition will be deferred until the thermal event has
been completed.
• If the P-state target frequency is lower than the processor IA core optimized target
frequency, the processor will transition to the P-state operating point.
5.1.5.1.3 Clock Modulation
If the frequency/voltage changes are unable to end an Adaptive Thermal Monitor
event, the Adaptive Thermal Monitor will utilize clock modulation. Clock modulation is
done by alternately turning the clocks off and on at a duty cycle (ratio between clock
“on” time and total time) specific to the processor. The duty cycle is factory configured
to 25% on and 75% off and cannot be modified. The period of the duty cycle is
configured to 32 microseconds when the Adaptive Thermal Monitor is active. Cycle
times are independent of processor frequency. A small amount of hysteresis has been
included to prevent excessive clock modulation 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 Adaptive
Thermal Monitor goes inactive and clock modulation ceases. Clock modulation is
automatically engaged as part of the Adaptive Thermal Monitor activation when the
frequency/voltage targets are at their minimum settings. Processor performance will be
decreased when clock modulation is active. Snooping and interrupt processing are
performed in the normal manner while the Adaptive Thermal Monitor is active.
Clock modulation will not be activated by the Package average temperature control
mechanism.