STM32H743 Weird screen flickering

[ktrofimo]

Using TouchGFX with FreeRTOS I got ​very strange screen flickering issue. For me it looks like broken LTDC buffer addresses, but I have no idea how it could happen.

https://youtu.be/sbEkdzT7yIc

Screen is updated few times every​ second.

And the thing what I can't understand is that code breaking screen has absolutely ​nothing related to LTDC or TouchGFX. For example, I can repair video by disabling one of the FreeRTOS tasks. Or comment out a function that does only some memory buffers initialization and moreover this function is not called for first 10 minutes of firmware uptime. But as soon as I uncomment this function call my screen become crazy. So it is more like kind of static memory issue.

Tasks stacks are placed in separate MCU memory region and all tasks have free stack space.​

[SofLit · Accepted solution]

Dear @ktrofimo​ ,

It smells the CM7 speculative access behavior.

Could you please disable the access to memory regions that are not used by your application using the MPU?

For more details about the issue and how to fix it, please refer to the AN4861 "Creating a graphical application with LTDC" / section 4.6 Special recommendations for Cortex-M7 (STM32F7/H7).

Also please refer to this thread: https://community.st.com/s/question/0D53W00001GlRzuSAF/information-about-mpu-settings-for-the-stm32h743

[ktrofimo]

Yes!

You are correct. My SDRAM memory was not cached and thus it was too slow for my task. Correct cache strategy made big difference!

Thanks!