User Guide

Datasheet, Volume 1 of 2 87
Thermal Management
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
. The DTS-relative temperature readout directly
impacts the Adaptive Thermal Monitor trigger point. When a package DTS indicates
that it has reached the TCC activation (a reading of 0x0, except when the TCC
activation offset is changed), the TCC will activate and indicate an Adaptive Thermal
Monitor event. A TCC activation will lower both processor IA core and graphics core
frequency, voltage, or both. Changes to the temperature can be detected using two
programmable thresholds located in the processor thermal MSRs. These thresholds
have the capability of generating interrupts using the processor IA core's local APIC.
Refer to the Intel 64 and IA-32 Architectures Software Developer’s Manual for specific
register and programming details.
5.1.5.2.1 Digital Thermal Sensor Accuracy (Taccuracy)
The error associated with DTS measurements will not exceed ±5 °C within the entire
operating range.
5.1.5.2.2 Fan Speed Control with Digital Thermal Sensor
Digital Thermal Sensor based fan speed control (T
FAN
) is a recommended feature to
achieve optimal thermal performance. At the T
FAN
temperature, Intel recommends full
cooling capability before the DTS reading reaches Tj
MAX
.
5.1.5.3 PROCHOT# Signal
PROCHOT# (processor hot) is asserted by the processor when the TCC is active. Only a
single PROCHOT# pin exists at a package level. When any DTS temperature reaches
the TCC activation temperature, the PROCHOT# signal will be asserted. PROCHOT#
assertion policies are independent of Adaptive Thermal Monitor enabling.