i.MX8M heat problem

[ollesandberg]

Hi,

We're using the i.MX8M (Quad) in a product connected to a 1080p LVDS display. We use Yocto as build system and a QT WebEngine based browser running in kiosk mode under Weston.

When we bring up a webpage in the browser and start scrolling the page (doesn't matter how simple the page is) after a short time (less than a minute) the GPU is overheated and the kernel reports:

[  930.557040] hantro receive hot notification event: 1
[  930.562170] System is too hot. GPU3D will work at 1/64 clock‍‍

We have a passive heat-sink attached to the CPU and no real CPU/GPU load except for the browser. With no user interaction the CPU temperature is ~70 C degrees and under interactions it goes up to around ~84 C before the GPU clock is decreased to 1/64.

Even if the browser is not running the CPU is idling on ~70 C degrees.

We have experienced the same problem with both a 4.9 kernel (Yocto Morty based build) and a newer 4.14 (Yocto Sumo based).

Has anyone else successfully used i.MX8M in a similar setup using passive cooling?

What can be done to lower the heat/power consumption?

BR, Olle

[tobias_wahl]

Hi Olle,

did you solve the problem?

We have nearly the same issue. We have a sumo configuration with no additional software or drivers, but the board is shutting down after a 25min cause of overheating. We tried several setups without heatsink but everytime the board is shutting down. Morty gives us better results than sumo, but not enough space for our applications. We can not accept the board shutting down in idle. So we need an solution for this.

Regards,
Tobias

[Yuri]

Hello,

  Do You use the recent i.MX8M silicon rev? 

Regards,

Yuri.

[ollesandberg]

Don't think we've got the most recent one yet. Is it supposed to lower the power consumption?

Is that the silicon used for the benchmarks in the post above?

[igorpadykov]

Hi Olle

one can try to test on NXP reference board, i.MX8M EVK with Demo Images on below link

and compare results with custom board. With a small form factor and low copper content,

compared with reference board, on custom board board heat dissipation can be issue.

Linux Binary Demo Files - i.MX 8MQuad EVK

Schematics
Design Files for the i.MX 8M Evaluation Kit (EVK)
i.MX 8M Evaluation Kit|NXP 

Some figures can be found in AN12118 i.MX8M Quad Power Consumption Measurement,

Coremark test, about 2W dissipation, die temperature = 60C, ambient temperature = 25 C.

KANZI test, about 3W dissipation die temperature = 67C, ambient temperature = 26 C.

https://www.nxp.com/docs/en/nxp/application-notes/AN12118.pdf 

Note, current greatly depends on temperature as described in

AN5381 Measuring Current in i.MX Applications sect.6.2. Current vs. ambient temperature
https://www.nxp.com/docs/en/application-note/AN5381.pdf

AN4579 Thermal Management Guidelines shows various thermal solutions
https://www.nxp.com/docs/en/application-note/AN4579.pdf

Best regards
igor
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