ETRA SOM/ETRA Hardware/Electrical Thermal and Mechanical Features/Thermal management and heat dissipation

History
Issue Date	Notes
2021/02/24	First Release
2023/08/03	Added Software thermal protection

Thermal management

The ETRA SOM is designed to support the maximum available temperature range declared by the manufacturer.

The customer shall define and conduct a reasonable number of tests and verification in order to qualify the DUT capabilities to manage the heat dissipation.

Any heatsink, fan etc shall be defined case by case.

DAVE Embedded Systems' team is available for any additional information, please contact sales@dave.eu.

Software thermal protection

In DESK-MP1-L, two software thermal protection mechanisms are implemented. Both are based on the processor's temperature sensor. It is worth remembering that maximum junction temperature (also denoted as Tj in the rest of the document) is:

• 105°C for extended commercial parts
• 125°C for industrial parts

ATF

At Arm Trusted Firmware level, automatic boot procedure is halted until Tj is smaller than (following temperatures might seem excessively low but they take into account the intrinsic poor precision of the temperature sensor to provide a reasonable safe margin):

Section not completed yet

Linux kernel

At Linux level, a more sophisticated protection mechanism is implemented. Please refer to the following sections for more details.

The default temperature threshold depend on the silicon grade, as follows:

• for industrial parts
  • critical threshold: 125°C

Practically speaking, for DESK-MP1-L this mechanism makes use of one threshold, denoted as trip_point0 (also known as critical threshold).

If Tj reaches trip_point0, a complete shutdown is triggered:

thermal thermal_zone0: cpu-thermal: critical temperature reached, shutting down

By default, temperature thresholds are set up as follows:

• trip_point0: 120°C

Trip point threshold can be accessed via sysfs interface from user space. The following example shows how to read the value of the trip point:

root@desk-mp1:~# cat /sys/devices/virtual/thermal/thermal_zone0/trip_point_0_temp
120000

This example shows how to set trip points 0 to 95°C:

echo 95000 > /sys/class/thermal/thermal_zone0/trip_point_0_temp

Please note that it is possible to set up trip points greater than the maximum junction temperature indicated by manufacturer datasheet exceeding maximum junction temperature indicated by manufacturer datasheet may cause permanent damage

To read current processor temperature please issue this command (reported temperature is 36.676°C in the example):

root@desk-mp1:~# cat /sys/class/thermal/thermal_zone0/temp
36676

For more details about this functionality, please refer to Documentation/thermal/sysfs-api.txt in the kernel sources.

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