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76 Intel® Xeon® Processor E5-1600 v2/E5-2600 v2 Product Families
Datasheet Volume One of Two
2.5.7.2 Interpretation
The resolution of the processor’s Digital Thermal Sensor (DTS) is approximately 1°C,
which can be confirmed by a RDMSR from the IA32_THERM_STATUS MSR where it is
architecturally defined. The MSR read will return only bits [13:6] of the PECI
temperature sensor data defined in Figure 2-50. PECI temperatures are sent through a
configurable low-pass filter prior to delivery in the GetTemp() response data. The
output of this filter produces temperatures at the full 1/64°C resolution even though
the DTS itself is not this accurate.
Temperature readings from the processor are always negative in a 2’s complement
format, and imply an offset from the processor T
Prochot
(PECI = 0). For example, if the
processor T
Prochot
is 100°C, a PECI thermal reading of -10 implies that the processor is
running at approximately 10°C below T
Prochot
or 90°C. PECI temperature readings are
not reliable at temperatures above T
Prochot
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 Celsius. A change of ‘1’ in the PECI count represents roughly a
temperature change of 1 degree Celsius. 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:
T
N
= (1-α) * T
N-1
+ α * T
SAMPLE
where T
N
and T
N-1
are the current and previous averaged PECI temperature values
respectively,
T
SAMPLE
is the current PECI temperature sample value and the variable
‘α’ = 1/2
X
, 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 Table 2-24.
§
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