hdmi Wrong colors and rendering output in HDMI with Linux base system

[Luighi Vitón]

Dear Digilent Engineers,

I am having a trouble when displaying images in the HDMI output. Although I tried to follow all the recommendations for the generation of the Zybo-base-linux project, the Linux kernel configuration and the devicetree, I had wrong colors and rendering in the HDMI output. I am using the Ubuntu based Linaro filesystem which comes with a graphical interface (I wonder it is the last version which have this feature).

Do you know which element could produce this behaviour and which changes I could apply to correct it. I attach a screenshot and a photo of my HDMI screen. I checked the cable and screen and those are correct. I also probed a precompiled image from the Zybot project and it shows a normal behaviour. However I need to add some modules to the base-linux so I have to compile it by myself.

Hope you could help to solve with this problem. Thanks.

[Luighi Vitón]

Hi @Ciprian,

After some time, I managed to solve this issue. In fact, It was a problem in the hardware and device tree configuration.

I discovered it when probing with another example project named Zybo-hdmi-out (https://github.com/Digilent/Zybo-hdmi-out). However, as this project is for a previous version of Vivado, I tested with Vivado 2017.4. Surprisingly, it worked fine but with another pixel-format in the device tree. The Zybo-base-linux project which I used, has a pixel format in DRM device tree configuration set to "rgb888", however, for the Zybo-hdmi-out, it displayed correctly with pixel-format "xrgb8888". If I use other pixel formats, no output is displayed in both cases. 

Going deep into the configuration of both projects, I discovered that there are some differences in the VDMA and Subset converter settings, which changed to the configuration in Zybo-hdmi-out, solves the problem of colors and rendering, considering also a pixel format in the devicetree equal to "xrgb8888". I attached the images of both configurations.

In addition to this, I managed to update the design for the Vivado version I use (2018.2) with no more differences that a change in the AXI memory interconnect replaced by the AXI Smart connect in the newer version, which is added automatically when using Vivado autoconnect tool for the VDMA block.

Hope this information could help others which run in the same issue. Thanks for your help.

Luighi Vitón 

[jpeyron]

Hi @Luighi Vitón,

Sorry for the delayed response. We reached out to more experienced embedded linux engineers about this thread. Unfortunately, They do not have any good suggestions at this point.

best regards,

Jon

[Ciprian]

Hi @Luighi Vitón,

I'm not sure it's a HDMI issue, have you tried to use X11 over SSH do you get the same result?

-Ciprian

[Ciprian]

Hi @Luighi Vitón,

Thanks for your reply and for your heads up, I'm glad you managed to get it working.

--Ciprian