14-26 Vol. 3B
POWER AND THERMAL MANAGEMENT
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Critical Temperature Log (bit 5, R/WC0) — Sticky bit that indicates whether the critical temperature
detector output signal has been asserted since the last clearing of this bit or reset. If bit 5 = 1, the output
signal has been asserted. Software may clear this bit by writing a zero.
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Thermal Threshold #1 Status (bit 6, RO) — Indicates whether the actual temperature is currently higher
than or equal to the value set in Thermal Threshold #1. If bit 6 = 0, the actual temperature is lower. If
bit 6 = 1, the actual temperature is greater than or equal to TT#1. Quantitative information of actual
temperature can be inferred from Digital Readout, bits 22:16.
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Thermal Threshold #1 Log (bit 7, R/WC0) — Sticky bit that indicates whether the Thermal Threshold #1
has been reached since the last clearing of this bit or a reset. If bit 7 = 1, the Threshold #1 has been reached.
Software may clear this bit by writing a zero.
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Thermal Threshold #2 Status (bit 8, RO) — Indicates whether actual temperature is currently higher than
or equal to the value set in Thermal Threshold #2. If bit 8 = 0, the actual temperature is lower. If bit 8 = 1, the
actual temperature is greater than or equal to TT#2. Quantitative information of actual temperature can be
inferred from Digital Readout, bits 22:16.
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Thermal Threshold #2 Log (bit 9, R/WC0) — Sticky bit that indicates whether the Thermal Threshold #2
has been reached since the last clearing of this bit or a reset. If bit 9 = 1, the Thermal Threshold #2 has been
reached. Software may clear this bit by writing a zero.
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Power Limitation Status (bit 10, RO) — Indicates whether the processor is currently operating below OS-
requested P-state (specified in IA32_PERF_CTL) or OS-requested clock modulation duty cycle (specified in
IA32_CLOCK_MODULATION). This field is supported only if CPUID.06H:EAX[bit 4] = 1. Package level power
limit notification can be delivered independently to IA32_PACKAGE_THERM_STATUS MSR.
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Power Notification Log (bit 11, R/WCO) — Sticky bit that indicates the processor went below OS-
requested P-state or OS-requested clock modulation duty cycle since the last clearing of this or RESET. This
field is supported only if CPUID.06H:EAX[bit 4] = 1. Package level power limit notification is indicated indepen-
dently in IA32_PACKAGE_THERM_STATUS MSR.
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Digital Readout (bits 22:16, RO) — Digital temperature reading in 1 degree Celsius relative to the TCC
activation temperature.
0: TCC Activation temperature,
1: (TCC Activation - 1) , etc. See the processor’s data sheet for details regarding TCC activation.
A lower reading in the Digital Readout field (bits 22:16) indicates a higher actual temperature.
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Resolution in Degrees Celsius (bits 30:27, RO) — Specifies the resolution (or tolerance) of the digital
thermal sensor. The value is in degrees Celsius. It is recommended that new threshold values be offset from the
current temperature by at least the resolution + 1 in order to avoid hysteresis of interrupt generation.
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Reading Valid (bit 31, RO) — Indicates if the digital readout in bits 22:16 is valid. The readout is valid if
bit 31 = 1.
Changes to temperature can be detected using two thresholds (see Figure 14-28); one is set above and the other
below the current temperature. These thresholds have the capability of generating interrupts using the core's local
APIC which software must then service. Note that the local APIC entries used by these thresholds are also used by
the Intel
®
Thermal Monitor; it is up to software to determine the source of a specific interrupt.