Thermal Specifications
Refer to the definition of each command in Section 6.3.2 for a specific definition of
possible command codes or FCS responses for a given command. The following
response policy definition is generic, and more advanced response policies may be
employed at the discretion of the originator developer.
Table 6-18. Originator Response Guidelines
Response
Bad FCS
After 1 Attempt
Retry
After 3 attempts
Fail with PECI client device error
Abort FCS
CC: Fail
Retry
Retry
Fail with PECI client device error. May be due to illegal command codes.
Either the PECI client doesn’t support the current command code, or it has
failed in its attempts to construct a response.
None (all 0’s) Force bus idle
(1ms low), retry
Fail with PECI client device error. Client may be dead or otherwise non-
responsive (in RESET or S1, for example).
CC: Pass
Pass
Pass
n/a
n/a
Good FCS
6.3.6
Temperature Data
6.3.6.1
Format
The temperature is formatted in a 16-bit, 2’s complement value representing a number
of 1/64 degrees centigrade. This format allows temperatures in a range of ±512°C to
be reported to approximately a 0.016°C resolution.
Figure 6-22. Temperature Sensor Data Format
MSB
MSB
LSB
LSB
Upper nibble
Lower nibble
Upper nibble
Lower nibble
S
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
Sign
Integer Value (0-511)
Fractional Value (~0.016)
6.3.6.2
Interpretation
The resolution of the processor’s Digital Thermal Sensor (DTS) is approximately 1°C,
which can be confirmed by a RDMSR from IA32_THERM_STATUS MSR (0x19C) where it
is architecturally defined. 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 reference TCC activation temperature. As an
example, assume that the TCC activation temperature reference is 100°C. A PECI
thermal reading of -10 indicates that the processor is running approximately 10°C
below the TCC activation temperature, or 90°C. PECI temperature readings are not
reliable at temperatures above TCC activation (since the processor is operating out of
specification at this temperature). Therefore, the readings are never positive.
6.3.6.3
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 4 Hz, it is necessary for the thermal readings to reflect thermal
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