Thermal Specifications and Design Considerations
80 Datasheet
5.3 Platform Environment Control Interface (PECI)
5.3.1 Introduction
PECI offers an interface for thermal monitoring of Intel processor and chipset
components. It uses a single wire; thus, alleviating routing congestion issues. 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.
5.3.1.1 T
CONTROL
and TCC Activation on PECI-Based Systems
Fan speed control solutions based on PECI use a T
CONTROL
value stored in the processor
IA32_TEMPERATURE_TARGET MSR. The T
CONTROL
MSR uses the same offset
temperature format as PECI though it contains no sign bit. Thermal management
devices should infer the T
CONTROL
value as negative. Thermal management algorithms
should use the relative temperature value delivered over PECI in conjunction with the
T
CONTROL
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 20. Conceptual Fan Control on PECI-Based Platforms
Min
Max
Fan Speed
(RPM)
T
CONTROL
Setting
TCC Activation
Temperature
PECI = 0
PECI = -10
PECI = -20
Temperature
Note: Not intended to depict actual implementation
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