PECI Interface

7PECI Interface

7.1Platform Environment Control Interface (PECI)

7.1.1Introduction

PECI uses a single wire for self-clocking and data transfer. The bus requires no additional control lines. The physical layer is a self-clocked one-wire bus that begins each bit with a driven, rising edge from an idle level near zero volts. The duration of the signal driven high depends on whether the bit value is a logic ‘0’ or logic ‘1’. PECI also includes variable data transfer rate established with every message. In this way, it is highly flexible even though underlying logic is simple.

The interface design was optimized for interfacing to Intel processors in both single processor and multiple processor environments. The single wire interface provides low board routing overhead for the multiple load connections in the congested routing area near the processor and chipset components. Bus speed, error checking, and low protocol overhead provides adequate link bandwidth and reliability to transfer critical device operating conditions and configuration information.

The PECI bus offers:

•A wide speed range from 2 Kbps to 2 Mbps

•CRC check byte used to efficiently and atomically confirm accurate data delivery

•Synchronization at the beginning of every message minimizes device timing accuracy requirements.

For single processor temperature monitoring and fan speed control management purposes, the PECI 3.0 commands that are commonly implemented includes Ping(),

GetDIB(), GetTemp(), TCONTROL and TjMax(TCC) read. The TCONTROL and TCC read command can be implemented by utilizing the RdPkgConfig() command.

7.1.1.1Fan Speed Control with Digital Thermal Sensor

Processor fan speed control is managed by comparing DTS temperature data against

the processor-specific value stored in the static variable, TCONTROL. When the DTS temperature data is less than TCONTROL, the fan speed control algorithm can reduce the speed of the thermal solution fan. This remains the same as with the previous guidance for fan speed control. Please refer to Section 6.1.6 for guidance where the DTS temperature data exceeds TCONTROL.

The DTS temperature data is delivered over PECI, in response to a GetTemp() command, and reported as a relative value to TCC activation target. The temperature data reported over PECI is always a negative value and represents a delta below the onset of thermal control circuit (TCC) activation, as indicated by the PROCHOT# signal. Therefore, as the temperature approaches TCC activation, the value approaches zero degrees.

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Thermal/Mechanical Specifications and Design Guidelines

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