Intel 64 and IA-32 Architectures Software Developers Manual Volume 3A, System Programming Guide, Part 1

13-6 Vol. 3A
POWER AND THERMAL MANAGEMENT
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.
13.4.1 Catastrophic Shutdown Detector
P6 family processors introduced a thermal sensor that acts as a catastrophic shut-
down detector. This catastrophic shutdown detector was also implemented in
Pentium 4, Intel Xeon and Pentium M processors. It is always enabled. When
processor core temperature reaches a factory preset level, the sensor trips and
processor execution is halted until after the next reset cycle.
13.4.2 Thermal Monitor
Pentium 4, Intel Xeon and Pentium M processors introduced a second temperature
sensor that is factory-calibrated to trip when the processor’s core temperature
crosses a level corresponding to the recommended thermal design envelop. The trip-
temperature of the second sensor is calibrated below the temperature assigned to
the catastrophic shutdown detector.
Figure 13-2. Processor Modulation Through Stop-Clock Mechanism
Clock Applied to Processor
Stop-Clock Duty Cycle
25% Duty Cycle (example only)