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===Software thermal protection ===
In [[DESK-MP1-L | 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):
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|'''Section not completed yet'''
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====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 [[ETRA_SOM/DESK-MP1-L | DESK-MX6-L]] this mechanism makes use of one threshold, denoted as <code>trip_point0</code> (also known as ''critical threshold'').
If Tj reaches <code>trip_point0</code>, a complete shutdown is triggered:
<pre>
thermal thermal_zone0: cpu-thermal: critical temperature reached, shutting down
</pre>
By default, temperature thresholds are set up as follows:
*<code>trip_point0</code>: 120°C
Trip point threshold can be accessed via <code>sysfs</code> interface from user space. The following example shows how to read the value of the trip point:
<pre>
root@desk-mp1:~# cat /sys/devices/virtual/thermal/thermal_zone0/trip_point_0_temp
120000
</pre>
This example shows how to set trip points 0 to 95°C:
<pre>
echo 95000 > /sys/class/thermal/thermal_zone0/trip_point_0_temp
</pre>
{{ImportantMessage|text=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):
<pre>
root@desk-mp1:~# cat /sys/class/thermal/thermal_zone0/temp
36676
</pre>
For more details about this functionality, please refer to <code>Documentation/thermal/sysfs-api.txt</code> in the kernel sources.
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[[Category:ETRA]]
