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5.2.1.3.4
Low-Power States and PROCHOT# Behavior
If the processor enters a low-power package idle state such as C3 or C6 with
PROCHOT# asserted, PROCHOT# will remain asserted until:
•
The processor exits the low-power state
•
The processor junction temperature drops below the thermal trip point
Note that the PECI interface is fully operational during all C-states and it is expected
that the platform continues to manage processor core thermals even during idle states
by regularly polling for thermal data over PECI.
5.2.1.4
On-Demand Mode
The processor provides an auxiliary mechanism that allows system software to force
the processor to reduce its power consumption via clock modulation. This mechanism is
referred to as "On-Demand" mode and is distinct from Adaptive Thermal Monitor and
bi-directional PROCHOT#. Platforms must not rely on software usage of this
mechanism to limit the processor temperature. On-Demand Mode can be done via
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.
5.2.1.4.1
MSR Based On-Demand Mode
If Bit 4 of the IA32_CLOCK_MODULATION MSR is set to a 1, the processor will
immediately reduce its power consumption via modulation of the internal core clock,
independent of the processor temperature. The duty cycle of the clock modulation is
programmable via Bits 3:1 of the same IA32_CLOCK_MODULATION MSR. In this mode,
the duty cycle can be programmed from 12.5% on/87.5% off to 87.5% on/12.5% off in
12.5% increments. Thermal throttling using this method will modulate each processor
core's clock independently.
5.2.1.4.2
I/O Emulation-Based On-Demand Mode
I/O emulation-based clock modulation provides legacy support for operating system
software that initiates clock modulation through I/O writes to ACPI defined processor
clock control registers on the chipset (PROC_CNT). Thermal throttling using this
method will modulate all processor cores simultaneously.
62
Thermal Management
Datasheet
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