Guide

Thermal and Mechanical Design
Intel® Xeon® Processor E7 2800/4800/8800 v2 Product Family 49
Thermal/ Mechanical Specifications and Design Guide
The PECI temperature reading from the processor can be compared to this T
CONTROL
value. A fan speed control scheme can be implemented as described in Table 2-14
without compromising the long-term reliability of the processor.
The PECI command for DTS is GetTemp(). Though use of a sign bit, the value returned
from PECI is negative.
The PECI command for T
CONTROL
is RdPkgConfig(), Temperature Target Read, 15:8. The
value returned from PECI is unsigned (positive), however is negative by definition.
There are many different ways of implementing fan speed control, including FSC based
on processor ambient temperature, FSC based on processor Digital Thermal Sensor
(DTS) temperature, or a combination of the two. If FSC is based only on the processor
ambient temperature, low acoustic targets can be achieved under low ambient
temperature conditions. However, the acoustics cannot be optimized based on the
behavior of the processor temperature. If FSC is based only on the Digital Thermal
Sensor, sustained temperatures above T
CONTROL
drive fans to maximum RPM. If FSC is
based both on the ambient and Digital Thermal Sensor, ambient temperature can be
used to scale the fan RPM controlled by the Digital Thermal Sensor. This would result in
an optimal acoustic performance. Regardless of which scheme is employed, system
designers must ensure that the Thermal Profile specification is met when the processor
Digital Thermal Sensor temperature exceeds the T
CONTOL
value for a given processor.
2.3.3 Tcontrol Relief
Near launch, Intel may provide T
CONTROL
Relief, in other words provide T
CONTROL
values
closer to 0, as compared to the factory configured T
CONTROL
values.
Factory configured T
CONTROL
values are available in the appropriate Dear Customer
Letter or may be extracted by issuing a Mailbox or an RDMSR instruction.
In some situations, use of T
CONTROL
Relief can reduce average fan power and improve
acoustics. There are no plans to change Intel's specification or the factory configured
T
CONTROL
values on individual processors.
Implementing T
CONTROL
Relief is optional. To implement this relief, customers must
rewrite the code and set the T
CONTROL
to the reduced values. Alternately, the factory
configured T
CONTROL
values or a value between the factory configured and the relief
guidance can still be used. Regardless of T
CONTROL
values used, BIOS needs to identify
the processor type.
Implementation of T
CONTROL
Relief maintains Intel standards of reliability (based on
modeling of the Intel Reference Design). Thermal Profile still applies. If PECI
>=T
CONTROL
Relief, then the temperature must meet the T
CASE
or the DTS based
Thermal Profile.
In some cases, use of T
CONTROL
Relief as the trigger point for fan speed control may
result in excessive TCC activation. To avoid this, the adjusted trigger point for fan
speed control (FSC) is defined as:
T
control_FSC
= - T
CONTROL
+ T
control_offset
T
control_offset
must be chosen such that T
control_FSC
< T
CONTROL
Relief. As such,
T
control_FSC
is an earlier trigger point for fan speed control, as compared to Tcontrol
Relief, and can be interpreted as over cooling. When over cooling to T
control_FSC
, margin
as defined in Section 2.2.3.2.1 and Section 2.2.3.2.5 can be ignored. Overcooling to
T
control_FSC
as compared to cooling to T
CONTROL
Relief: