LCD flicker following new FW being flashed

[jchernus-fikst]

Hi all,

I have a screen with an RGB interface (Focus LCD E35KA-FW1000-N) that's being driven by an STM32H747 with the framebuffer in external RAM (over FMC). I'm presently using a double framebuffer strategy, but this same behaviour occurs when I used single.

After flashing new FW, the screen flickers quite badly, and then over a few minutes it settles down and I have a beautiful screen with immediate transitions and no flickering. While it's flickering, you'll see the previous image it was displaying in the background. I'm not too worried about this, it disappears once the flicker is gone.

What could be causing this? 

I can't share the project (under NDA), but I'll gladly answer any relevant questions that can help someone help me solve this. Thanks in advance,

Julia

[GaetanGodart]

Hello @jchernus-fikst ,

 

Can you share your setup parameter for the screen?
Perhaps your LTDC configurations?

This datasheet : https://www.hpinfotech.ro/ILI9488.pdf tells you some timings to follow :

 

Is the horizontal synchronization, vertical back porch and DOTCLK Frequency correctly setup?

 

Regards,

[jchernus-fikst]

Hey @GaetanGodart,

Thanks for responding. Here is the information you asked for:

The values for the first two sections, "Synchronization for Width" and "Synchronization for Height" were provided by Focus LCD. The Signal Polarity I worked out myself.

The DOTCLK frequency is set to 12,307692MHz, which is just above 389 x 507 x 62 = 12.227.826

I believe these all to be within the acceptable bounds. Like I mentioned in my last post - the screen performs wonderfully a few minutes after flashing and has no artifacts during a power cycle. It only happens while flashing.

My problem with this behaviour is that it sticks around for several minutes and looks unprofessional, so I need to fix this before we get this product into the hands of Beta customers. 

Thanks for your help!

Julia

 

[jchernus-fikst]

Some more settings, in case they're relevant - to avoid going back and forth.

More from LTDC

TouchGFX

DMA2D

Thanks again!

Julia

[jchernus-fikst]

@GaetanGodart any suggestions for how to proceed? Thanks!

[GaetanGodart]

Hello @jchernus-fikst ,

 

Just checking in, did you manage to fix your display flickering?

 

Regards,

[jchernus-fikst]

Hi Gaetan,

No, every time we flash the unit with new FW, it flashes back at us for ~2 minutes. We decided we could live with it through some user-research and early prototypes, but now we're moving onto Beta and I need to get it fixed.

To answer your previous questions,

I am resetting the screen (hard & soft) on every initialization.

I tried increasing the DOTCLK and it made no difference, I'm within the range you shared, 10-20MHz.

We are operating at a VSYNC_FREQ of 16ms, i.e. ~60fps.

 

Thank you,

Julia

[Tesla DeLorean]

Does flickering occur in the non-TouchGFX cases, ie you just painting a static (or different) images from the frame buffer?

Say a more stand-alone example like the PicturesFromSD, etc that come in the Cube repos for DISCO, DK and EVAL boards?

Not sure what TouchGFX would be doing in the minutes after an Internal/External memory update that wouldn't be occurring at every other power cycle.