STM32 How to use LTDC

[kulfi27]

Hi, I designed a board with uC STM32H743 that works with a 480x800 display connected through the LTDC peripheral, I don't quite know how to use the LTDC, I don't have ram for the buffer of the entire display. What I can do is fill the background with color, but on layer1 I can only display one buffer at a time, when I display another one, the previous one disappears. In various videos I see that even small uCs can handle a larger display without a large buffer. My question is, what should the procedure for loading smaller buffers into layer1 look like?

[MM..1]

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@kulfi27 wrote:

uCs can handle a larger display without a large buffer.

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you miss, this is valid only for displays with internal frame memory. Or for displays with sloooow refresh rate.

743 provides 1 to 2 Mbytes Flash memory, 1 Mbyte of SRAM with the following architecture: 192 Kbytes of TCM RAM (including 64 Kbytes of ITCM RAM and 128 Kbytes of DTCM RAM for time-critical routines and data), 512 Kbytes, 288 Kbytes and 64 Kbytes of user SRAM ...

I see here plenty space for one L8 or 565 framebuffer, when your display dont have internal memory...

 

[kulfi27]

Thank you for your response, I already understand how the LTDC peripheral is supposed to work. I don't know how to place data in other sectors of SRAM, the compiler loads everything into RAM_D1 memory. Can someone help me with this issue?

[Tesla DeLorean]

Does your design include a screen with it's own controller and buffer, or are you trying to send R G B signals to the pane?

LTDC is primarily a frame buffer DMA unit

Small uC's typically use panels with their own frame buffer, and you manipulate that, either moving bit maps, or painting/drawing type primitives implemented on the controller.

[kulfi27]

I'm using LTDC to drive an 800x480 RGB565 display. Due to limited internal RAM and LTDC being able to access only SDRAM1 (512KB), I implemented partial screen updates using two 800x160 buffers and the LTDC line interrupt.

Each frame is split into 3 sections (160 lines each). In the LTDC line interrupt, I switch buffers and update the and to display one section at a time. The switching works for the first two sections (0 and 1), but the third section (2) shows only the background color — missing all text or drawn content.WVPCRCFBAR

When debugging step-by-step with breakpoints, the missing content does appear correctly, which suggests a timing/synchronization issue.

It seems that LTDC may require buffer and window updates to be applied ahead of time (before it starts drawing the section). I tried updating , , and triggering in the line interrupt and even pre-setting the to fire ~20 lines earlier, but the problem persists.CFBARWVPCRSRCRLIPCR

Any suggestions on the correct timing to safely update LTDC layer address and window region before a partial refresh?