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Thermal Specifications and Design Considerations

Datasheet

5.4

Platform Environment Control Interface (PECI)

5.4.1

Introduction

PECI offers an interface for thermal monitoring of Intel processor and chipset

components. It uses a single wire, thus alleviating routing congestion issues. Figure 19

shows an example of the PECI topology in a system. PECI uses CRC checking on the

host side to ensure reliable transfers between the host and client devices. Also, data

transfer speeds across the PECI interface are negotiable within a wide range (2 Kbps to

2 Mbps). The PECI interface on the processor is disabled by default and must be

enabled through BIOS.

5.4.1.1

Key Difference with Legacy Diode-Based Thermal Management

Fan speed control solutions based on PECI uses a TCONTROL value stored in the

processor IA32_TEMPERATURE_TARGET MSR. The TCONTROL MSR uses the same offset

temperature format as PECI though it contains no sign bit. Thermal management

devices should infer the TCONTROL value as negative. Thermal management algorithms

should use the relative temperature value delivered over PECI in conjunction with the

TCONTROL MSR value to control or optimize fan speeds. Figure 20 shows a conceptual

fan control diagram using PECI temperatures.

The relative temperature value reported over PECI represents the delta below the onset

of thermal control circuit (TCC) activation as indicated by PROCHOT# assertions. As the

temperature approaches TCC activation, the PECI value approaches zero. TCC activates

at a PECI count of zero.

Figure 19.

Processor PECI Topology

PECI Host

Controller

Land G5

Domain 0

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