User Guide

Datasheet, Volume 1 of 2 89

Thermal Management

5.1.5.7 Low-Power States and PROCHOT# Behavior

Depending on package power levels during package C-states, outbound PROCHOT#

may de-assert while the processor is idle as power is removed from the signal. Upon

wake up, if the processor is still hot, the PROCHOT# will re-assert. Although, typically

package idle state residency should resolve any thermal issues. The PECI interface is

fully operational during all C-states and it is expected that the platform continues to

manage processor IA core and package thermals even during idle states by regularly

polling for thermal data over PECI.

5.1.5.8 THERMTRIP# Signal

Regardless of enabling the automatic or on-demand modes, in the event of a

catastrophic cooling failure, the package will automatically shut down when the silicon

has reached an elevated temperature that risks physical damage to the product. At this

point, the THERMTRIP# signal will go active.

5.1.5.9 Critical Temperature Detection

Critical Temperature detection is performed by monitoring the package temperature.

This feature is intended for graceful shutdown before the THERMTRIP# is activated.

However, the processor execution is not guaranteed between critical temperature and

THERMTRIP#. If the Adaptive Thermal Monitor is triggered and the temperature

remains high, a critical temperature status and sticky bit are latched in the

PACKAGE_THERM_STATUS MSR 1B1h and the condition also generates a thermal

interrupt, if enabled. For more details on the interrupt mechanism, refer to the Intel

64 and IA-32 Architectures Software Developer’s Manual (see Related Documents

section).

5.1.5.10 On-Demand Mode

The processor provides an auxiliary mechanism that allows system software to force

the processor to reduce its power consumption using clock modulation. This

mechanism is referred to as “On-Demand” mode and is distinct from Adaptive Thermal

Monitor and bi-directional PROCHOT#. The processor platforms should not rely on

software usage of this mechanism to limit the processor temperature. On-Demand

Mode can be accomplished using processor MSR or chipset I/O emulation. On-Demand

Mode may be used in conjunction with the Adaptive Thermal Monitor. However, if the

system software tries to enable On-Demand mode at the same time the TCC is

engaged, the factory configured duty cycle of the TCC will override the duty cycle

selected by the On-Demand mode. If the I/O based and MSR-based On-Demand modes

are in conflict, the duty cycle selected by the I/O emulation-based On-Demand mode

will take precedence over the MSR-based On-Demand Mode.

5.1.5.11 MSR Based On-Demand Mode

If Bit 4 of the IA32_CLOCK_MODULATION MSR is set to 1, the processor will

immediately reduce its power consumption using modulation of the internal processor

IA core clock, independent of the processor temperature. The duty cycle of the clock

modulation is programmable using bits [3:1] of the same IA32_CLOCK_MODULATION

MSR. In this mode, the duty cycle can be programmed in either 12.5% or 6.25%

increments (discoverable using CPUID). Thermal throttling using this method will

modulate each processor IA core's clock independently.