STM32F7 LTDC Flickering

I turn D-Cache on with the standard CMSIS function (SCB_EnableDCache). Don't know about FMC/SDRAM cache. And yes, I write to SDRAM directly from CPU (SDRAM is memory mapped to 0xD0000000). I draw the graphics in it and than copy it with DMA2D to the screen buffer. All these operations are synchronized so there is no concurrency access to SDRAM. For instance, if I would write to SDRAM in other task in parallel I will receive heavy screen flickering all the time.

It seems to me that it is some strange internal CPU overload for some operations like FPU or context switch. And in this particular overload tick LTDC skips its scan/refresh cycle. Flickr could happen once in a minute or 20 minutes, or 5 times per second. It depends on, I think, instructions sequence. For example, on 746 it was a situation where I clear the rectangural area in black and than write some digits in white and it heavy glitches, but when I clear the same area in blue - it works fine. It sounds crazy but it was.

Moreover, on 767 with double precision flickrs happen much rarely than when the program was compiled with single precision.

Now I know that disabled D-Cache helps. But application speed is slow. I need to optimize it.

And I plan to change all the ariphmetics to soft FPU and try.

If your floating point calculations are part of your screen rendering, the D-Cache accelerates your code, but may delay the content of your screen. Flush the D-Cache with SCB_CleanDCache(); after you finished your Screen calculations and before you swap the Screen buffers.

Had the same Problems with STM32F7, same code worked fine on a STM32F4.

Dear

Turvey.Clive.002

I'll try to enable FPUwhich you toldwith me.

Thank you.