Data Sheet

Thermal Management
94 Datasheet, Volume 1 of 2
• If the P-state target frequency is lower than the processor IA core optimized target
frequency, the processor will transition to the P-state operating point.
5.1.5.1.3 Clock Modulation
If the frequency/voltage changes are unable to end an Adaptive Thermal Monitor event,
the Adaptive Thermal Monitor will utilize clock modulation. Clock modulation is done by
alternately turning the clocks off and on at a duty cycle (ratio between clock “on” time
and total time) specific to the processor. The duty cycle is factory configured to 25% on
and 75% off and cannot be modified. The period of the duty cycle is configured to 32
microseconds when the Adaptive Thermal Monitor is active. Cycle times are
independent of processor frequency. A small amount of hysteresis has been included to
prevent excessive clock modulation when the processor temperature is near its
maximum operating temperature. Once the temperature has dropped below the
maximum operating temperature, and the hysteresis timer has expired, the Adaptive
Thermal Monitor goes inactive and clock modulation ceases. Clock modulation is
automatically engaged as part of the Adaptive Thermal Monitor activation when the
frequency/voltage targets are at their minimum settings. Processor performance will be
decreased when clock modulation is active. Snooping and interrupt processing are
performed in the normal manner while the Adaptive Thermal Monitor is active.
Clock modulation will not be activated by the Package average temperature control
mechanism.
5.1.5.2 Digital Thermal Sensor
Each processor has multiple on-die Digital Thermal Sensor (DTS) that detects the
processor IA, GT and other areas of interest instantaneous temperature.
Temperature values from the DTS can be retrieved through:
• A software interface using processor Model Specific Register (MSR).
• A processor hardware interface as described in Platform Environmental Control
Interface (PECI).
When temperature is retrieved by the processor MSR, it is the instantaneous
temperature of the given DTS. When temperature is retrieved using PECI, it is the
average of the highest DTS temperature in the package over a 256 ms time window.
Intel recommends using the PECI reported temperature for platform thermal control
that benefits from averaging, such as fan speed control. The average DTS temperature
may not be a good indicator of package Adaptive Thermal Monitor activation or rapid
increases in temperature that triggers the Out of Specification status bit within the
PACKAGE_THERM_STATUS MSR 1B1h and IA32_THERM_STATUS MSR 19Ch.
Code execution is halted in C1 or deeper C- states. Package temperature can still be
monitored through PECI in lower C-states.
Unlike traditional thermal devices, the DTS outputs a temperature relative to the
maximum supported operating temperature of the processor (Tj
MAX
), regardless of TCC
activation offset. It is the responsibility of software to convert the relative temperature
to an absolute temperature. The absolute reference temperature is readable in the
TEMPERATURE_TARGET MSR 1A2h. The temperature returned by the DTS is an implied
negative integer indicating the relative offset from Tj
MAX
. The DTS does not report
temperatures greater than Tj
MAX
. Refer to the appropriate processor family BIOS
Specification (Refer Related Documents section) for specific register details. The DTS-
relative temperature readout directly impacts the Adaptive Thermal Monitor trigger