screen jumps horizontally (2-3mm) every so often during fast update

Question

Hi,

We have developed a custom system based on the STM32F429 evaluation board, it is working fine for the most part. It is single tasking, with a main loop. We use rotary dials to control  information updates on the screen, sometime, but not always, during fast updates, the screen jumps momentarily horizontally. Obviously some sort of timing issue, is there way to synchronize updates to the screen? or some pointers  on where to look resolve this issue. I am processing the rotary dials  with Timer 3 interrupts at 1KHz, plus  I don't call Embedded Wizard functions from my interrupt, but do I send information to the  uart just after enabling a flag for Embedded Wizard to update the screen.

Any suggestions would be greatly appreciated.

MikeZ

Answer 1

Hi Mike,

typically, this indicates an LTDC buffer underflow. Sometimes, while the DMA2D is executing a lot of drawing operations, the display content appears horizontally shifted at a certain display line.

Is this the effect that you have on your hardware? Maybe you can post a short video sequence.

In case of LTDC buffer underflow, the problem is not related to the GUI software itself - this is more a problem of the system memory bandwidth. The LTDC does not get enough data from memory and the synchronization is lost.

What is the display size that you are using? What color format are you using?

Is your SDRAM connected as 16bit or 32bit memory?

Maybe you can try to reduce the pixel frequency - does this improve the effect?

Best regards,

Manfred.

Comments

Hi Manfred,

Thanks for your response,sorry for the delay in replying. It seems to match your description. Reducing the  pixel frequency does indeed improve things, since it was much worse originally. The SDRAM is  connected as 16-bit,  the format is RGB888, the display and  has a resolution of 480x272. I will experiment further and try to make a video.

Thanks

MikeZ