Intel IA-32 - Manual (Page 516)

13-6 Vol. 3A
POWER AND THERMAL MANAGEMENT
13.4.1 Catastrophic Shutdown Detector
P6 family processors introduced a thermal sensor that acts as a catastrophic shutdown 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 cali-
brated below the temperature assigned to the catastrophic shutdown detector.
13.4.2.1 Thermal Monitor 1
The Pentium 4 processor uses the second temperature sensor in conjunction with a mechanism
called TM1 (Thermal Monitor 1) 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.
13.4.2.2 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. 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.
Support for TM2 is indicated by CPUID.1:ECX.TM2[bit 8] = 1.
13.4.2.3 Two Methods for Enabling TM2
On processors with CPUID family/model/stepping signature encoded as 0x69n or 0x6Dn (early
Pentium M processors), TM2 is enabled if the TM_SELECT flag (bit 16) of the