Sporadic screen distortions on stm32f7 with SDRAM

[Zed]

Hi everyone!
Can you guys help me to identify the reason of the strange screen distortions that I’m getting from time to time on my custom board based on stm32f746 with external SDRAM. The display is controlled by LTDC controller.
 

Example of distortions

Has it something to do with LTDC controller or with SDRAM?
I appreciate any help!
THX

[PeterVang]

Hello Zed,

I is difficult to tell based on this one screenshot. My first guess is LTDC underrun, caused by the RAM bandwidth being to low to support the display resolution. Can you give more information about your setup, like:

• Display resolution
• Color depth
• Framebuffer strategy
• RAM interface bandwidth

Best regards,

Peter

[Zed]

Hi Peter,
thank you very much for your response!

• Display resolution is 800x480
• Color depth 16bit = 565 mode
• Framebuffer is controlled by STemWin
• RAM interface is 16 bit wide at 100MHz, total of 32Mb

For reasons that had nothing to do with display distortions we had to remove “defect” MCU and soldered a new one and after that all screen distortions were gone. Anyway, I would be glad to hear every idea why such distortions may happen.
THX

[Ejack1979]

we had to remove “defect” MCU and soldered a new one and after that all screen distortions were gone.

Sounds like an issue of poor soldering…
If mass-producted you should pay more attention to similar cases and product batch yield.