Intel ARCHITECTURE IA-32 User Manual download pdf (Page 521)

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Vol. 3A 13-11

POWER AND THERMAL MANAGEMENT

13.4.4 Detection of Thermal Monitor and Software Controlled

Clock Modulation Facilities

The ACPI flag (bit 22) of the CPUID feature flags indicates the presence of the

IA32_THERM_STATUS, IA32_THERM_INTERRUPT, IA32_CLOCK_MODULATION

MSRs, and the xAPIC thermal LVT entry.

The TM1 flag (bit 29) of the CPUID feature flags indicates the presence of the automatic thermal

monitoring facilities that modulate clock duty cycles.

13.4.5 On Die Digital Thermal Sensors

On die digital thermal sensor can be read using an MSR (no I/O interface). In Intel Core Duo

processors, each core has a unique digital sensor whose temperature is accessible using an MSR.

The digital thermal sensor is the preferred method for reading the die temperature because (a) it

is located closer to the hottest portions of the die, (b) it enables software to accurately track the

die temperature and the potential activation of thermal throttling.

13.4.5.1 Digital Thermal Sensor Enumeration

The processor supports a digital thermal sensor if CPUID.06H.EAX[0] = 1. If the processor

supports digital thermal sensor, EBX[bits 3:0] determine the number of thermal thresholds that

are available for use.

Software sets thermal thresholds by using the IA32_THERM_INTERRUPT MSR. Software

reads output of the digital thermal sensor using the IA32_THERM_STATUS MSR.

13.4.5.2 Reading the Digital Sensor

Unlike traditional analog thermal devices, the output of the digital thermal sensor is a tempera-

ture relative to the maximum supported operating temperature of the processor ( Tj(Max), as

specified in the processor’s data sheet). It is software’s responsibility to convert the relative

temperature to an absolute temperature.

Temperature measurements returned by digital thermal sensors are always at or below Tj(Max).

Over temperature conditions are detected using the out-of-spec status bit. When this bit is set,

the processor is operating out of specification and immediate shutdown of the system should

occur. Once the out-of-spec status bit is set, reliable operation is not guaranteed.

See Figure 13-8 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

1 2 ... 516 517 518 519 520 521 522 523 524 525 526 ... 635 636

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