DAVE Embedded Systems' team is available for any additional information, please contact [mailto:sales@dave.eu sales@dave.eu].
===Software thermal protection ''TODO: verificare l'implementazione nel BSP'' ===
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 commercial and industrial parts
*125°C for automotive parts.
====U-Boot====
At U-Boot 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):
*90 for commercial and industrial parts
*110°C for automotive parts.
====Linux kernel====
At Linux level, a more sophisticated protection mechanism is implemented. Please refer to the following sections for more details.
The default temperature thresholds depend on the silicon grade, as follows:
*for commercial and industrial parts
** passive threshold: 95°C
** critical threshold: 100°C
*for automotive parts
** passive threshold: 115°C
** critical threshold: 120°C.
Practically speaking, for DESK-MP1-L this mechanism makes use of two different thresholds, denoted as <code>trip_point0</code> (also known as ''passive threshold'') and <code>trip_point1</code> (also known as ''critical threshold''.
When Tj reaches <code>trip_point0</code>, Linux kernel scales down processor frequency:
<pre>
System is too hot. GPU3D will work at 1/64 clock.
</pre>
If Tj reaches <code>trip_point1</code>, a complete shutdown is triggered:
<pre>
thermal thermal_zone0: critical temperature reached(100 C),shutting down
</pre>
By default, temperature thresholds are set up as follows:
*<code>trip_point0</code>: 85°C
*<code>trip_point1</code>: 100°C.
Trip point thresholds can be accessed via <code>sysfs</code> interface from user space. The following example shows how to read the values of the trip points:
<pre>
root@axel-lite:~# cat /sys/devices/virtual/thermal/thermal_zone0/trip_point_0_temp
85000
root@axel-lite:~# cat /sys/devices/virtual/thermal/thermal_zone0/trip_point_1_temp
100000
</pre>
This example shows how to set trip points 0 and 1 to 95°C and 100°C respectively:
<pre>
echo 95000 > /sys/class/thermal/thermal_zone0/trip_point_0_temp
echo 100000 > /sys/class/thermal/thermal_zone0/trip_point_1_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@axel-lite:~# 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]]
