Intel ARCHITECTURE IA-32 User Manual download pdf (Page 523)

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101

Vol. 3A 13-13

POWER AND THERMAL MANAGEMENT

• 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.

• Digital Readout (bits 22:16, RO) — Digital temperature reading in 1 degree Celsius

relative to Tj(Max). 0 = Tj(Max); 1 = Tj(Max) - 1

C; etc. See the processor’s data sheet

for details regarding Tj(Max).

• 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.

• 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 13-9); 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.

See Figure 13-9 for the layout of IA32_THERM_INTERRUPT MSR. Bit fields include:

• High-Temperature Interrupt Enable (bit 0, R/W) — This bit allows the BIOS to enable

the generation of an interrupt on the transition from low-temperature to a high-temperature

threshold. Bit 0 = 0 (default) disables interrupts; bit 0 = 1 enables interrupts.

• Low-Temperature Interrupt Enable (bit 1, R/W) — This bit allows the BIOS to enable

the generation of an interrupt on the transition from high-temperature to a low-temper-

ature. Bit 0 = 0 (default) disables interrupts; bit 0 = 1 enables interrupts.

Figure 13-9. IA32_THERM_INTERRUPT Register

Reserved

Threshold #2 Interrupt Enable

12345814

16222324

Threshold #2 Value

Threshold #1 Interrupt Enable

Threshold #1 Value

Overheat Interrupt Enable

FORCPR# Interrupt Enable

THERMTRIP Interrupt Enable

Low Temp. Interrupt Enable

High Temp. Interrupt Enable

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Intel ARCHITECTURE IA-32 User Manual Page 523

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