Intel P8700 Data Sheet - Page 111
Digital Thermal Sensor, PROCHOT# will not be asserted when the processor is in the Stop Grant
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Thermal Specifications and Design Considerations 5.1.3 Besides the thermal sensor and thermal control circuit, the Intel Thermal Monitor also includes one ACPI register, one performance counter register, three MSR, and one I/O pin (PROCHOT#). All are available to monitor and control the state of the Intel Thermal Monitor feature. The Intel Thermal Monitor can be configured to generate an interrupt upon the assertion or deassertion of PROCHOT#. PROCHOT# will not be asserted when the processor is in the Stop Grant, Sleep, Deep Sleep, and Deeper Sleep low-power states, hence the thermal diode reading must be used as a safeguard to maintain the processor junction temperature within maximum specification. If the platform thermal solution is not able to maintain the processor junction temperature within the maximum specification, the system must initiate an orderly shutdown to prevent damage. If the processor enters one of the above low-power states with PROCHOT# already asserted, PROCHOT# will remain asserted until the processor exits the low-power state and the processor junction temperature drops below the thermal trip point. However, PROCHOT# will de-assert for the duration of Deep Power Down Technology state (C6) residency. If Thermal Monitor automatic mode is disabled, the processor will be operating out of specification. Regardless of enabling the automatic or on-demand modes, in the event of a catastrophic cooling failure, the processor will automatically shut down when the silicon has reached a temperature of approximately 125 °C. At this point the THERMTRIP# signal will go active. THERMTRIP# activation is independent of processor activity and does not generate any bus cycles. When THERMTRIP# is asserted, the processor core voltage must be shut down within the time specified in Chapter 3. In all cases the Intel Thermal Monitor feature must be enabled for the processor to remain within specification. Digital Thermal Sensor The processor also contains an on-die Digital Thermal Sensor (DTS) that can be read via an MSR (no I/O interface). Each core of the processor will have a unique digital thermal sensor whose temperature is accessible via the processor MSRs. The DTS is the preferred method of reading the processor die temperature since it can be located much closer to the hottest portions of the die and can thus more accurately track the die temperature and potential activation of processor core clock modulation via the Thermal Monitor. The DTS is only valid while the processor is in the normal operating state (the Normal package level low-power state). Unlike traditional thermal devices, the DTS outputs a temperature relative to the maximum supported operating temperature of the processor (TJ,max). It is the responsibility of software to convert the relative temperature to an absolute temperature. The temperature returned by the DTS will always be at or below TJ,max. Catastrophic temperature conditions are detectable via an Out Of Specification status bit. This bit is also part of the DTS MSR. When this bit is set, the processor is operating out of specification and immediate shutdown of the system should occur. The processor operation and code execution is not ensured once the activation of the Out of Specification status bit is set. The DTS-relative temperature readout corresponds to the Thermal Monitor (TM1/TM2) trigger point. When the DTS indicates maximum processor core temperature has been reached, the TM1 or TM2 hardware thermal control mechanism will activate. The DTS and TM1/TM2 temperature may not correspond to the thermal diode reading since the thermal diode is located in a separate portion of the die and thermal gradient between the individual core DTS. Additionally, the thermal gradient from DTS to thermal diode can vary substantially due to changes in processor power, mechanical and thermal attach, and software application. The system designer is required to use the DTS to ensure proper operation of the processor within its temperature operating specifications. Datasheet 111