STM32F479 datasheet(44/91 Pages) STMICROELECTRONICS

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Creating a graphical application with LTDC

AN4861

44/91

DocID029237 Rev 2

Example: 480 x 272 display with 24 bpp

For a 480 x 272 display (the frame line width is 480 pixels) and with a 24 bpp color depth,

the line width size is equal to 1440 bytes which is not a multiple of 64 bytes.

Note:

For that resolution, to have a multiple line width size of 64 bytes, the user can use another

color depth such as RGB565.

Since the frame line is composed of 22 bursts of 64 bytes and one 32 bytes burst, the 10th

burst of the second line of the frame crosses the Kilobyte boundary. This leads to the split of

the read operation into single accesses.

The Figure 25 illustrates the kilobyte boundary cross problem for the given example.

Figure 25. Burst access crossing the kilobyte boundary

For this example we describe the two methods to solve the crossing Kilobyte boundary

issue:

•

Reduce the layer window and the framebuffer line widths: use the LTDC layer

windowing feature by reducing the window size to match the closest frame line width

multiple of 64 bytes.

Since the window width is reduced, the framebuffer size should also be reduced since

the extra 22 and 23 bursts for all frame lines are not fetched nor displayed by LTDC.

This method solves the 1 Kbyte boundary crossing issue with a slight window width

decrease (see Figure 26).

The code below is based on the HAL drivers and shows an example of setting the pitch

as described in Figure 26:

/* Setting the Layer1 window to 448x272 at positions X = 16 and Y = 0 */

pLayerCfg.WindowX0 = 16;

pLayerCfg.WindowX1 = 464;

pLayerCfg.WindowY0 = 0;

pLayerCfg.WindowY1 = 272;

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