Screen tearing

Question

Dear Embedded wizard support,

 

I am the following problem:

The screen will tear when the platform is moving, otherwise i have a clean picture.

The ball moving does not create tear.

Touching the screen to move the platform will also create tear.

    

 

Any suggestions how to solve for this would be appreciated! 

 

Thank you in advance!

Answer 1

Hello,

it seems to be a memory bandwidth issue. As soon as the DMA2D is transferring large memory areas, the LTDC does not get enough data. The result is a buffer underflow and a flickering on the display.

I think we had a similar discussion, but a couple of answers were missing. Maybe you can provide a summary of your target:

What color format of the framebuffer are you using?

What is the screen size?

What size of SDRAM are you using?

How is the SDRAM connected (16 or 32 bit)?

What MCU are you using?

What Embedded Wizard version are you using?

Best regards,

Manfred.

Comments

What color format of the framebuffer are you using?

i am using RGB888, this is because of the Telerex 800x480 interface comes with 8xR, 8xG, and 8xB data lines.

What is the screen size?

The screen size is 800x480.

What size of SDRAM are you using?

The SDRAM size is 8MB (256Mb, or 0x800000), the chip is IS42S32800J, same as on the stm32f756-g-EVAL.

How is the SDRAM connected (16 or 32 bit)?

SDRAM is connected as default, 32 bit.

What MCU are you using?

Instead of the STM32F756-g i am using the SMT32F767BIT6 (is compatible, but why it is chosen i heard is because of memory issues).

What Embedded Wizard version are you using?

Using Embedded Wizard free edition 9.30.

(to get the platform running before purchasing any PRO edition, we have very old 7.10 PRO, but never used). 

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i changed it to RGB565 as suggested often times by Embedded wizard experts.

then the result is better, but i have 'embedded wizard evaluation edition' graphic not as clean as in the rgb888 version, and i suspect this will again result in the circle from the https://ask.embedded-wizard.de/4835/example-projects-not-working-smooth which is a similar element as the 'embedded wizard evaluation edition' graphic.

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i think problem is solved now, 

happend because project is setup in stm32-cubeide, and the linker for libegfx-m7-gcc still was using RGB888 instead of newly selected RGB565!

 

ALSO CIRCLE IS WORKING NOW!

 

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Great to hear! Of course, you should use the suitable library and the suitable header files / source codes!

Concerning the RGB888, let me recommend the AN4861 from ST - there you will find some additional information to optimize the SDRAM access and LTDC configuration. For example in case of RGB888 the framebuffer width should have a multiple of 64 bytes. This means in case of 800x480 display size, you should try to set the framebuffer width to 832 pixel (there is no need to change the ScreenSize within the GUI project).

Best regards.

Manfred.

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Thank you, 

i have rgb888 working now also!

​​​​​​​

 

 

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i have looked a little further, different examples and now i have yellow vertical lines instead of white lines.

 

this is on RGB565 aswell as RGB888.

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What do you mean with yellow vertical lines? How do they look? Are these lines statically or do they appear dynamically (just for one frame) and disappear?

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Here these horizontal grid/table lines should be white.

on the previous page i have this problem also, static, but only for right side now,

they stay, on RGB888 they look a bit corrupted (not straight line).

 

 

edit:

i think i have caused this problem, not solved yet but i have some attempts which i need to restore.

edit 2:

problem is gone,