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Vol. 3 14-19
POWER AND THERMAL MANAGEMENT
14.5.5.2 Reading the Digital Sensor
Unlike traditional analog thermal devices, the output of the digital thermal sensor is
a temperature relative to the maximum supported operating temperature of the
processor.
Temperature measurements returned by digital thermal sensors are always at or
below TCC activation temperature. Critical temperature conditions are detected
using the “Critical Temperature Status” bit. When this bit is set, the processor is
operating at a critical temperature and immediate shutdown of the system should
occur. Once the “Critical Temperature Status” bit is set, reliable operation is not guar
-
anteed.
See Figure 14-11 for the layout of IA32_THERM_STATUS MSR. Bit fields include:
• Thermal Status (bit 0, RO) — This bit indicates whether the digital thermal
sensor high-temperature output signal (PROCHOT#) is currently active. Bit 0 = 1
indicates the feature is active. This bit may not be written by software; it reflects
the state of the digital thermal sensor.
• Thermal Status Log (bit 1, R/WC0) — This is a sticky bit that indicates the
history of the thermal sensor high temperature output signal (PROCHOT#).
Bit 1 = 1 if PROCHOT# has been asserted since a previous RESET or the last time
software cleared the bit. Software may clear this bit by writing a zero.
• PROCHOT# or FORCEPR# Event (bit 2, RO) — Indicates whether PROCHOT#
or FORCEPR# is being asserted by another agent on the platform.
Figure 14-11. IA32_THERM_STATUS Register
63
0
Reserved
15
Reading Valid
12345810
16222327
Resolution in Deg. Celsius
Digital Readout
Thermal Threshold #2 Log
Thermal Threshold #2 Status
Thermal Threshold #1 Log
Thermal Threshold #1 Status
Critical Temperature Log
679
3132
Critical Temperature Status
PROCHOT# or FORCEPR# Log
PROCHOT# or FORCEPR# Event
Thermal Status Log
Thermal Status