Display Artefacts

Question

Hello,

out application is running on one kind of hardware. No we have to verify another display. On this hardware, the display shows concentric circles within the lower black part of the image:

Also this image is flickering, but only at black/grey parts of the picture.

We did a lot of measurement on the signal lines, but the signals seem to be ok.

The real image looks like this.It has a slow transition from black at the border to grey in the middle:

Comments

Also it's very strange, that the display is only working, if we use maximum 19,2 MHz clock. For higher clock rates there is no display on both types of hardware.

Is this related to the EW grahics system or the used RGBA8888 format?

There is no difference, when I switch double buffering on or off.

Answer 1

Hello,

it's difficult to give you good advices based on the provided information...

I assume that the display is connected only with 5 or 6 bits per color component or that the display is only able to show colors in RGB565 format or you are using the color format RGB565 within your profile.

In all cases your radial gradients will result in some radial color steps.

In you can verify that when you place some color gradients into your application - as it is shown within the example 'ColorFormats' that is provided in all Build Environments:

In case of RGB565 you will see color steps:

Best regards,

Manfred Schweyer.

 

 

Comments

Thanks Mafred,

it seems your right:

Since I do use RGBA8888 in my profile and this is displayed correctly on our first choice of hardware, there must be an issue with the other hardware.

One additional question:

We tried some different clock settings and realized, that the EW app stopps loading, when the screen refresh rate exceeds 20 Hz:

Initialize Graphics Engine...                System halted! [HardFault_Handler]

Is this correlated to the SDRAM rate?

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If you are changing the entire system clock configuration it will have an impact to more units than the display. If you are just changing the LTDC settings, this will not influence the timing of other hardware parts. Of course it will have an impact to the memory bandwidth, but this is another topic.

Let me refer to the tool CubeMX that is used to create proper clock settings for your target.

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OK, I understand this. We just changed the display clock.

Is there any limitation, that EW is not capable of displaying at a higher refresh rate than 40Hz?

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There is no limitation from Embedded Wizard point of view concerning the display refresh rate or the graphics performance.