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FAQ : possible display resolutions for STM32MP1

The STM32MP1 data sheet states that maximum display resolution for the LTDC controller is WXGA @60 frames /s with RGB888 pixel format.

Can STM32MP1 support other display configurations ?

Background
 

The maximum display resolution depends on the Soc bus architecture, the DDR controller and the display controller.

The STM32MP15 can support a pixel stream from a frame buffer located in DRAM into display interface with a maximum pixel clock of 90Mhz with pixels in RGB888 format.

 

The pixel clock frequency correspond to the frequency of the pixel sent to the display.

The display refresh rate defines the number of pixel displayed each second (fps).

Generally its is 60 fps and can be modified.

To display a picture each second, the display expects some blanking period with virtual pixels (no real pixels, called vertical and horizontal 'porchs'  in figure below) and period with active pixels corresponding to the pixels of the image transmitted.  Generally the banking periods lasts 40% of a frame period, this depends on the panel, and can be shorter.

 

1.png

 

answer

 

So the maximum display resolution for RGB888 pixels is such :

Display pixel width X Display nb of lines X fps X 1.4  <= maximum STM32MP1 pixel clockie 90Mhz

 

So, for example a display  1366 x 768 @ 60fps needs a pixel clock 1366*768*60*1.4 = 88MHz Display 1280 x 800 @ 60fps needs to 86MHz, is also fine.

 

One can support higher resolution by reducing the display refresh rate or the display blanking period (tolerance depending on display).

One can support various display pixel width/display nb of lines without any issue.

 

The maximum drawing rate is number of time per second the GPU or the A7 can redraw in frame buffer. Note this highly depends on the GUI application and graphical software stack optimizations. The higher the drawing rate is, the better the GUI will be fluid.

  

 

Keyword STM32MP1 WXGA , display, resolution, LTDC

Version history
Last update:
‎2020-04-06 06:28 AM