Reduce Display EMC/ Verify Pinmux

Technical Support
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1

Hello!

I’m currently trying to reduce the Display EMC. According to the following guides

I need to modify the device-tree.

So I modified the lines 651-672 in the following file: imx6qdl-colibri.dtsi « dts « boot « arm « arch - linux-toradex.git - Linux kernel for Apalis, Colibri and Verdin modules
I set all values to 0x8 (Speed: Low, DSE: 150 Ohm, SRE: Slow), which should be the lowest possible value.
After that, i created a patch, and applied it to our build system, build the image and flashed it.
I still have a working display so I would like to verify the new pinmux, How do I do that?
I was able to find the node in /proc and also got a dump with hexdump, but I don’t know how to compare it with my modified pinmux.

hexdump of the device tree node:

root@colibri-imx6:~# hexdump -C /proc/device-tree/soc/aips-bus@02000000/iomuxc@020e0000/ipu1/ipu1grp-lcd/fsl,pins
00000000  00 00 00 9c 00 00 03 b0  00 00 00 00 00 00 00 00  |................|
00000010  00 00 00 00 00 00 00 08  00 00 00 a0 00 00 03 b4  |................|
00000020  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 08  |................|
00000030  00 00 00 a4 00 00 03 b8  00 00 00 00 00 00 00 00  |................|
00000040  00 00 00 00 00 00 00 08  00 00 00 a8 00 00 03 bc  |................|
00000050  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 08  |................|
00000060  00 00 00 b0 00 00 03 c4  00 00 00 00 00 00 00 00  |................|
00000070  00 00 00 00 00 00 00 08  00 00 00 b4 00 00 03 c8  |................|
00000080  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 08  |................|
00000090  00 00 00 e0 00 00 03 f4  00 00 00 00 00 00 00 00  |................|
000000a0  00 00 00 00 00 00 00 08  00 00 00 f4 00 00 04 08  |................|
000000b0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 08  |................|
000000c0  00 00 00 f8 00 00 04 0c  00 00 00 00 00 00 00 00  |................|
000000d0  00 00 00 00 00 00 00 08  00 00 00 fc 00 00 04 10  |................|
000000e0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 08  |................|
000000f0  00 00 01 00 00 00 04 14  00 00 00 00 00 00 00 00  |................|
00000100  00 00 00 00 00 00 00 08  00 00 01 04 00 00 04 18  |................|
00000110  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 08  |................|
00000120  00 00 01 08 00 00 04 1c  00 00 00 00 00 00 00 00  |................|
00000130  00 00 00 00 00 00 00 08  00 00 01 0c 00 00 04 20  |............... |
00000140  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 08  |................|
00000150  00 00 00 b8 00 00 03 cc  00 00 00 00 00 00 00 00  |................|
00000160  00 00 00 00 00 00 00 08  00 00 00 bc 00 00 03 d0  |................|
00000170  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 08  |................|
00000180  00 00 00 c0 00 00 03 d4  00 00 00 00 00 00 00 00  |................|
00000190  00 00 00 00 00 00 00 08  00 00 00 c4 00 00 03 d8  |................|
000001a0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 08  |................|
000001b0  00 00 00 c8 00 00 03 dc  00 00 00 00 00 00 00 00  |................|
000001c0  00 00 00 00 00 00 00 08  00 00 00 cc 00 00 03 e0  |................|
000001d0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 08  |................|
000001e0  00 00 00 d0 00 00 03 e4  00 00 00 00 00 00 00 00  |................|
000001f0  00 00 00 00 00 00 00 08  00 00 00 d4 00 00 03 e8  |................|
00000200  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 08  |................|
00000210

EDIT: Okay I found a way. The hexdump contains 00 00 00 08 exactly 22 times, which is the amount of lines i modified and set to 0x8. So I am assuming, that I successfully modified the device tree. Just one last question: Is my described way the correct one, to reduce the EMC of the display?

2

hi @cheesi

Perfect that you’re able to check if you applied the device tree correctly.

Concerning EMC, your new settings should reduce EMC. Just you have to check if your image is still correctly displayed on the screen. If not, then you have to change the settings till you get a good image.

For EMC reducing, you could also add shielding around the display cable and connect this shielding to Ground.

Best regards
Jaski

3

Hi @jaski.tx !

Thanks for your answer. Display works well.

Also thanks for the advice about shielding, we already included that after our last laboratory test.

BR Christian

4

Perfect, that it works. Thanks for the feedback.