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Vol. 3 14-11
POWER AND THERMAL MANAGEMENT
consumption; this is in addition to the reduction offered by automatic thermal
monitoring mechanisms.
4. On-die digital thermal sensor and interrupt mechanisms permit the OS to
manage thermal conditions natively without relying on BIOS or other system
board components.
The first mechanism is not visible to software. The other three mechanisms are
visible to software using processor feature information returned by executing CPUID
with EAX = 1.
The second mechanism includes:
• Automatic thermal monitoring provides two modes of operation. One mode
modulates the clock duty cycle; the second mode changes the processor’s
frequency. Both modes are used to control the core temperature of the processor.
• Adaptive thermal monitoring can provide flexible thermal management on
processors made of multiple cores.
The third mechanism modulates the clock duty cycle of the processor. As shown in
Figure 14-5, the phrase ‘duty cycle’ does not refer to the actual duty cycle of the
clock signal. Instead it refers to the time period during which the clock signal is
allowed to drive the processor chip. By using the stop clock mechanism to control
how often the processor is clocked, processor power consumption can be modulated.
For previous automatic thermal monitoring mechanisms, software controlled mecha-
nisms that changed processor operating parameters to impact changes in thermal
conditions. Software did not have native access to the native thermal condition of the
processor; nor could software alter the trigger condition that initiated software
program control.
The fourth mechanism (listed above) provides access to an on-die digital thermal
sensor using a model-specific register and uses an interrupt mechanism to alert soft
-
ware to initiate digital thermal monitoring.
Figure 14-5. Processor Modulation Through Stop-Clock Mechanism
Clock Applied to Processor
Stop-Clock Duty Cycle
25% Duty Cycle (example only)