64-bit Intel Xeon Processorwith 1MB L2 Cache Thermal/Mechanical Design Guidelines

R
Thermal/Mechanical Reference Design
64-bit Intel
®
Xeon™ Processor MP with 1 MB L2 Cache 13
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 MP with 1 MB L2 cache, the Tcontrol 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:
T
CONTROL
= T
CONTROL_BASE
+ Offset Equation 2
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.
The T
CONTROL_BASE
value for this processor is 50°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 2-4 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
).
Figure 2-4. T
CONTROL
and Thermal Profile Interaction
Pcontrol_base
TDP
T
CASE
T
CASE
MAX
T
CASE
@
Pcontrol_base
Power
Thermal Profile
T
CASE
@ T
CONTROL
Pcontrol
1
2
Pcontrol_base
TDP
T
CASE
T
CASE
MAX
T
CASE
@
Pcontrol_base
Power
Thermal Profile
T
CASE
@ T
CONTROL
Pcontrol
1
2
T
CASE
MAX @
T
CONTROL
T
CASE
MAX @
Pcontrol_base
T
CASE
MAX
Pcontrol_base
TDP
T
CASE
T
CASE
MAX
T
CASE
@
Pcontrol_base
Power
Thermal Profile
T
CASE
@ T
CONTROL
Pcontrol
1
2
Pcontrol_base
TDP
T
CASE
T
CASE
MAX
T
CASE
@
Pcontrol_base
Power
Thermal Profile
T
CASE
@ T
CONTROL
Pcontrol
1
2
T
CASE
MAX @
T
CONTROL
T
CASE
MAX @
Pcontrol_base
T
CASE
MAX
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
, the case temperature is permitted to exceed the Thermal Profile,
but the diode temperature must remain at or below T
CONTROL
. In other words, there is no T
CASE
specification for the processor at power levels less than Pcontrol. The thermal solution for the
processor must be able to keep the processor’s T
CASE
at or below the T
CASE
values defined by the