Thermal Considerations
VL-EPU-3311 Reference Manual
56
The decision as to which thermal solution to use can be based on several factors including:
Number of CPU cores in the SoC (single, dual, or quad)
CPU and video processing utilization by the user application
Temperature range within which the EPU-3311 will be operated
Air movement (or lack of air movement)
Most of these factors involve the demands of the user application on the EPU-3311 and cannot
be isolated from the overall thermal performance. Due to the interaction of the user application,
the Osprey thermal solution, and the overall environment of the end system, thermal performance
cannot be rigidly defined.
The ambient air surrounding the EPU-3311 needs to be maintained at 85 ºC or below. This
would include the space between the two main boards as well as the space beneath an installed
Mini PCIe expansion board. Standard methods for addressing this requirement include the
following:
Provide a typical airflow of 100 linear feet per minute (LFM) / 0.5 linear meters per second
(as described in the section titled EPU-3311 Thermal Characterization, beginning on page
59) within the enclosure
Position the EPU-3311 board to allow for convective airflow
Lower the system level temperature requirement as needed
CPU Thermal Trip Points
The CPU cores in the Osprey have their own thermal sensors. Coupled with these sensors are
specific reactions to three thermal trip points. Table 16 describes the three thermal trip points.
Note that these are internal temperatures that are about 10 ºC above the heat plate temperature.
Table 16: CPU Thermal Trip Points
Trip Point
Description
Passive (Note 1)
At this temperature, the CPU cores throttle back to a lower speed. This
reduces the power draw and heat dissipation, but lowers the processing
speed.
Critical (Note 2)
At this temperature, the operating system typically puts the board into a
sleep or other low-power state.
Maximum core temperature
The CPU turns itself off when this temperature is reached. This is a fixed
trip point and cannot be adjusted.
Notes:
1. The default value in the BIOS Setup utility for this trip point is 90 ºC.
2. The default value in the BIOS Setup utility for this trip point is 100 ºC.
These trip points allow maximum CPU operational performance while maintaining the lowest
CPU temperature possible. The long-term reliability of any electronic component is degraded
when it is continually run near its maximum thermal limit. Ideally, the CPU core temperatures
will be kept well below 100 ºC with only brief excursions above.
CPU temperature monitoring programs are available to run under both Windows and Linux.
Table 17 lists some of these hardware monitoring programs.
