Only getting background color on the screen. No other graphic images appear.

[TSton]

I'm trying to get a new display board working. It has an STM32F469, and external SDRAM. Using STM32CubeIDE and TouchGFX to generate code. So far, all I get on the screen is a filled background color, as set it in LTDC settings. No other graphics . Does this mean that at least the external SDRAM and frame buffer are working correctly? I'm trying to narrow down where to look for the problem since every part of this task is new.  

[Martin KJELDSEN]

That looks a bit different than the original one you showed me. Is it looking as you expect?

[TSton]

Yes. That's what I expect. I had to recreate the screen from the first time I posted it, so it is a little different. But what about the underrun interrupt? Is that something to worry about? Or can I just disable it at startup?

[TSton]

Yes. That is what I expected. I had to manually recreate the screen and didn't make it exactly the same. But about the underrun interrupt. Do I need to worry about that?

[TSton]

Also, I replaced the test boxes on the screen with the actual graphic that I need, a company logo that I can't post here, and now the logo is a jittery mess across the screen. If I lower the pixel clock down to 24MHz, was 38MHz, the image is stable, but I get a visible flicker on the screen. How do I compensate for that? I'm running the processor and SDRAM at 166MHz, which is the fasted allowed on the RAM.

[Martin KJELDSEN]

Hi, well, this smells like memory contention now that we're talking about images, so the LTDC and DMA2D are accessing the ram at the same time. What you've done by reducing the pixel clock (Any other speeds that work up to a max of 38 MHZ?) is slow down the VSYNC a bit which relieves the pressure a bit.

Now you can try to go full speed on pixel clock and then hal.lockDMAToFrontPorch(true); - This will tell us if DMA2D/LTDC have issues accessing memory at same time.

/Martin

[TSton]

Hi Martin,

I tried going back to 38MHz, and locking DMA to front porch, but I still get a scrambled image instead.

Terry