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14-12 Vol. 3
POWER AND THERMAL MANAGEMENT
14.5.1 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.
14.5.2 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.
14.5.2.1 Thermal Monitor 1
The Pentium 4 processor uses the second temperature sensor in conjunction with a
mechanism called Thermal Monitor 1 (TM1) to control the core temperature of the
processor. TM1 controls the processor’s temperature by modulating the duty cycle of
the processor clock. Modulation of duty cycles is processor model specific. Note that
the processors STPCLK# pin is not used here; the stop-clock circuitry is controlled
internally.
Support for TM1 is indicated by CPUID.1:EDX.TM[bit 29] = 1.
TM1 is enabled by setting the thermal-monitor enable flag (bit 3) in
IA32_MISC_ENABLE [see Appendix B, “Model-Specific Registers (MSRs)”]. Following
a power-up or reset, the flag is cleared, disabling TM1. BIOS is required to enable
only one automatic thermal monitoring modes. Operating systems and applications
must not disable the operation of these mechanisms.
14.5.2.2 Thermal Monitor 2
An additional automatic thermal protection mechanism, called Thermal Monitor 2
(TM2), was introduced in the Intel Pentium M processor and also incorporated in
newer models of the Pentium 4 processor family. Intel Core Duo and Solo processors,
and Intel Core 2 Duo processor family all support TM1 and TM2. TM2 controls the
core temperature of the processor by reducing the operating frequency and voltage
of the processor and offers a higher performance level for a given level of power
reduction than TM1.
TM2 is triggered by the same temperature sensor as TM1. The mechanism to enable
TM2 may be implemented differently across various IA-32 processor families with
different CPUID signatures in the family encoding value, but will be uniform within an
IA-32 processor family.