Intel® Xeon® Processor E5-1600/E5-2600/E5-4600 Product Families 77
Datasheet Volume One
Temperature readings from the processor are always negative in a 2’s complement
format, and imply an offset from the processor Tjmax (PECI = 0). For example, if the
processor Tjmax is 100°C, a PECI thermal reading of -10 implies that the processor is
running at approximately 10°C below Tjmax or at 90°C. PECI temperature readings are
not reliable at temperatures above Tjmax since the processor is outside its operating
range and hence, PECI temperature readings are never positive.
The changes in PECI data counts are approximately linear in relation to changes in
temperature in degrees centigrade. A change of ‘1’ in the PECI count represents
roughly a temperature change of 1 degree centigrade. This linearity is approximate and
cannot be guaranteed over the entire range of PECI temperatures, especially as the
offset from the maximum PECI temperature (zero) increases.
2.5.7.3 Temperature Filtering
The processor digital thermal sensor (DTS) provides an improved capability to monitor
device hot spots, which inherently leads to more varying temperature readings over
short time intervals. Coupled with the fact that typical fan speed controllers may only
read temperatures at 4Hz, it is necessary for the thermal readings to reflect thermal
trends and not instantaneous readings. Therefore, PECI supports a configurable low-
pass temperature filtering function that is expressed by the equation:
TN = (1-α) * TN-1 + α * TSAMPLE
where TN and TN-1 are the current and previous averaged PECI temperature values
respectively, TSAMPLE is the current PECI temperature sample value and the variable
‘α’ = 1/2X, where ‘X’ is the ‘Thermal Averaging Constant’ that is programmable as
described in Section 2.5.2.6.21.
2.5.7.4 Reserved Values
Several values well out of the operational range are reserved to signal temperature
sensor errors. These are summarized in Tabl e 2-24 .
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Table 2-24. Error Codes and Descriptions
Error Code Description
0x8000 General Sensor Error (GSE)
0x8001 Reserved
0x8002 Sensor is operational, but has detected a temperature below its operational range
(underflow)
0x8003-0x81ff Reserved