Display corruption problem with async update using ST7735_t3 library (using an ST7796 on a T4.1)

M

Mike Chambers

Well-known member
I got this 4" 320x480 ST7796 LCD from Amazon. I'm trying to use it in my project, but whenever I try to use the async display mode to speed things up, the output is complete garbage.

I'm initializing the tft with this:

C: 
// For 3.5" or 4.0" TFT with ST7796
ST7796_t3 tft = ST7796_t3(TFT_CS, TFT_DC, TFT_RST);

And here's my code for the init:

C: 
  tft.init(320, 480);
  tft.fillScreen(ST7735_BLACK);
  tft.setRotation(3);
  tft.useFrameBuffer(true);
  fbout = tft.getFrameBuffer();

Then when I fill in fbout and use tft.updateScreen() as in the non-async one, it looks perfect, like this:

PXL_20250530_031927401.jpg


All is well and good, right? Well, when I change that line to tft.updateScreenAsync(false); then it looks like this. If you look closely, there are a few messed up blue lines at the top. You can see a few white pixels in there from some of the text too.

PXL_20250530_032120965.jpg


Any idea what's wrong? Is the library just broken for the ST7796? If so, how do I fix it? I really, really need async. Normal update is just too slow for this project.
 
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