We have a Technexion pico-imx7d with QCA wifi/bt in our device, and we're running Linux 4.9 build with Yocto (Technexion BSP).
We notice that during idling in linux the cpu load is approx 1-5%, but the core temp reaches 52°C which is a lot!
When we compare to Raspberry PI 3 (quad core), this idles at 42°C. Considering IMX7D is a low power chip, this outcome is far from expected. This becomes problematic for us when we deploy our devices in summer, when ambient temperature increases to over 65°C instead of the ambient temperature of approx 20-25°C that we currently have in our labs. The system will be triggered into shutdown!
I've noticed Application Notes such AN5317, AN5388 and i.MX Linux Reference Manual.
From what I can tell, dynamic cpu frequency scaling and DVFS is working, and cpu is running at 800MHz most of the time. Available frequencies are 800 and 1000 MHz. The guess the Cortex M4 is also disabled:
root@pico-imx7:~# devmem2 0x30390000 w
Memory mapped at address 0x76f01000.
Read at address 0x30390000 (0x76f01000): 0x000000A0
What other tricks do we have in software to lower the thermal output / power usage?
Sleep is no option.