When we use the default configuration for HDMI-related parameters, the HDMI eye diagram test fails.
I have read in the Jetson Nano Interface Tuning and Compliance Guide that it can be solved by strengthening the driver and pre-emphasis.
Therefore, I want to confirm whether our adjustment is effective first, so that it makes sense to test it in the laboratory. But even after I adjust the values of the 4 LANEs of 0x54580138 to 0XFF, the swing measured by the oscilloscope does not change. Does this achieve the purpose of enhancing the driver?
If tuning both drive current and pre-emphasis can not make change on voltage swing, it might mean your hardware has some problem. You may need to check/change the design of HDMI. Some customer reported that changing choke is helpful.
If the values of the four LANEs of 0x54580138 are adjusted to 0xFF, is its swing expected to increase?
Our current common mode choke is 90ohm@100MHz, are you saying that its impedance is too high?
Yes, swing is expected to increase. Did you try more other values of drive current? Also you can try shorting choke. Anyway, you may need to try more hardware changes besides tuning register.
Sorry, I passed on the wrong information. The previous modification did not actually take effect, so it is reasonable to test that there is no change in swing.
But after I changed it to the default value as shown in the attached picture, the display is not output. What should I check? Do you have any suggestions?
Did you try more other values? Did you try shorting chokes?
Yes, we tried changing the values of all 4 LANE to 0xFF, but it didn’t show up either. Then we changed them to default values, but it didn’t show up either.
We haven’t shorted the common chock yet, because we want to confirm whether changing the software can solve our problem first.
You can try more other values than FF or default. Software might not solve this as it could be related to hardware design. But at least you can try more settings.
In addition to FF and the default value, we also tried more other values, but all of them resulted in no display on the HDMI port. Perhaps we can only try to change the common chock with a lower impedance.
But we still want to confirm that the HDMI port can display normally without this code, but after adding this code to the code, HDMI cannot display. Is it because I added the code to the wrong position? How should I confirm whether the position where my code is added is correct?
As I remember the prod setting of Jetson Nano could be put into device tree but not directly into driver code.
Hello, I checked the code for “nvidia,drive-current”, it seems only working for DP output. Is there any method to adjust the parameters for HDMI connector ? See the following codes.
please just put your register change to tegra210-prods.dtsi.
Hi, It is all right now. Thank you for the information.
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