Guide

Thermal and Mechanical Design
44 Intel® Xeon® Processor E7 2800/4800/8800 v2 Product Family
Thermal/ Mechanical Specifications and Design Guide
The recommended time interval between energy readings is 1 second. This helps
ensure the power calculation is accurate by making the error between time stamps
small as compared to the duration between time stamps.
The PECI command for energy is RdPkgConfig(), the service is called Accumulated CPU
Energy, the bit numbers 31:0.
2.2.3.2.3 Averaging the DTS Based Thermal Specification
Averaging the DTS Based Thermal Specification helps keep the rate of change of the
temperature specification on the same scale as the actual processor temperature, and
helps avoid rapid changes in fan speed when power changes rapidly.
An exponential average of the specification can be calculated using a two time constant
model:
T
DTS_f
= α
f
x Δt x T
DTS_max
+ T
DTS_f_previous
x (1- α
f
x Δt)
T
DTS_s
= α
s
x Δt x T
DTS_max
+ T
DTS_s_previous
x (1- α
s
x Δt)
T
DTS_ave
= C x T
DTS_f
x (1-C) x T
DTS_s
Where:
T
DTS_max
is the instantaneous spec
T
DTS_f
and T
DTS_s
are the fast and slow time averages
T
DTS_ave
is the final two time constant average specification
α
f
and α
s
are the time constant coefficients
C is a scale factor
Δt is the scan rate and is recommended to be approximately 1 second
Table 2-11 below shows the initial coefficients recommended for averaging. These
values may change per processor SKU. Customers should tune these coefficients based
on their thermal solutions.
2.2.3.2.4 Absolute Processor Temperature
Intel does not test any third party software that reports absolute processor
temperature. As such, Intel cannot recommend the use of software that claims this
capability. Since there is part-to-part variation in the TCC (thermal control circuit)
activation temperature, use of software that reports absolute temperature can be
misleading.
Please consult the BIOS Writer’s Guide for details regarding the use of the
IA32_TEMPERATURE_TARGET register which reports the minimum absolute
temperature at which the TCC will be activated and PROCHOT# will be asserted. The
IA32_TEMPERATURE_TARGET register may be different for each processor SKU.
2.2.3.2.5 Considerations for Follow-on Processor
The follow-on processor will have new capabilities as compared to Intel® Xeon®
Processor E7 2800/4800/8800 v2 Product FamilySheet. As such, customers may want
to write fan speed control algorithms that are tolerant of the follow-on processor’s
capabilities.
For the follow-on processor, the intercept and slope terms from the T
DTS
equations
(T
LA
, Ψ
pa
), as defined in Section 2.2.3.2.1, are stored in the processor. This allows
margin (M) to be reported by the processor. The PECI command for margin (M) will be
RdPkgConfig(), Index 10.
M < 0; gap to spec, fan speed must increase