64-bit Intel Xeon Processor with 2MB L2 Cache Thermal/Mechanical Design Guidelines

Thermal/Mechanical Reference Design
16 64-bit Intel® Xeon™ Processor with 2MB L2 Cache Thermal/Mechanical Design Guidelines
2.2.2 T
CONTROL
Definition
T
CONTROL
is a temperature specification based on a temperature reading from the processor’s
thermal diode. T
CONTROL
defines the lower end of the Thermal Profile line for a given processor,
and it can be described as a trigger point for fan speed control implementation. The value for
T
CONTROL
is calibrated in manufacturing and configured for each processor individually. For the
64-bit Intel Xeon Processor with 2MB L2 Cache, the T
CONTROL
value is obtained by reading a
processor model specific register (MSR) and adding this offset value to a base value. The equation
for calculating T
CONTROL
is:
Equation 2-2. T
CONTROL
= T
CONTROL_BASE
+ Offset
Where:
T
CONTROL_BASE
=A fixed base value defined for a given processor generation as published in
the processor datasheet.
Offset= A value programmed into each processor during manufacturing that can be
obtained by reading the IA32_TEMPERATURE_TARGET MSR. This is a static and a unique
value. Refer to the
IA-32 Intel
®
Architecture Software Developer's Manual Volume 3:
System Programming Guide
for further details.
The T
CONTROL_BASE
value for the 64-bit Intel Xeon Processor with 2MB L2 Cache is 50
o
C. The
Offset value, which depends on several factors (i.e. leakage current), can be any number between 0
and (T
CASE
MAX - T
CONTROL_BASE
). Figure 2-3 depicts the interaction between the Thermal
Profile and T
CONTROL
for an Offset value that is greater than 0 (i.e. T
CONTROL
greater than
T
CONTROL_BASE
).
Since T
CONTROL
is a processor diode temperature value, an equivalent T
CASE
temperature must be
determined to plot the T
CASE
MAX @ T
CONTROL
point on the Thermal Profile graph. Location 1
on the Thermal Profile represents a T
CASE
value corresponding to an Offset of 0 (the theoretical
minimum for the given processor family). Any Offset value greater than 0 moves the point where
the Thermal Profile must be met upwards, as shown by location 2 on the graph. If the diode
temperature is less than T
CONTROL
, then the case temperature is permitted to exceed the Thermal
Figure 2-3. T
CONTROL
and Thermal Profile Interaction