STM32H747XI: Is it possible to use a MIPI screen with greater resolution than the max. of 1024x768

[ELegr.2]

Hi,

For a POC, we want to connect a MIPI screen with resolution of 1280x720 but the datasheet of the STM32H747XI states "LCD-TFT controller up to XGA resolution".

XGA resolution is 1024x768.

Is this max resolution is a hardware limitation (due to memory or bandwith) or this can be overcome with some drawbacks (as lower framerate for example) ?

[Tesla DeLorean]

It's ultimately a bandwidth thing.

The DSI ceiling for 16bpp is 62.5 MHz pixel clock, 41.66 MHz for 24 bpp

You'd want 32-bit wide SDRAM

Yes you can drop the frame rate to 25 or 30 Hz if the display supports that.

Seem to recall getting some 1388x768 and 1280x720 modes working on the F7 boards, the configuration is very flexible, the display just needs to be agreeable. Check the spec sheets.

[Robmar]

Okay but not everyone is using DSI and it's differentially serial signalling, many are using the standard RGB(888) HV parallel interfaces to their LCDs, which will easily support higher resolutions than XGA.
Of course the MCU will need more than the current maximum 512KB internal RAM on the AXI bus to support XGA resolution, the datasheet states:
"The LCD-TFT display controller, LTDC, uses a 64-bit bus, connected to the AXI bus matrix, through which it can access internal AXI SRAM and Flash memories, and external memories through the Octo-SPI controller and the FMC."  Does it state that it can access RAM not mapped directly onto the AXI bus, such as RAM shared between ITCM and AXI and TCM RAM, and if it could, what would be the performance hit?
Anyway, the FMC memory controller can support two banks of 128 MB SDRAM, why can't that be used with the LCD controller for RGB interfaces at much higher resolutions than XGA?

[Tesla DeLorean]

The OP was specifically asking about MIPI-DSI. I don't recall saying SDRAM couldn't be used.

Pretty much any large resolution display for the STM32 series is going to be using external memory, and the pins counts for RGB and SDRAM get to be quite large pushing into more exotic part packages and boards. There's very little flexibility in the pin choices, so escaping these, and getting a workable mix of parts is going to be a challenge. ie Getting 2x 256MB and 24-bit RGB sounds good on paper, going to be a difficult board.

The LTDC is limited by the counter widths rather than VGA, XGA dimensions. Its more a game then of meeting the min/max refresh rates and pixel clocks, and not overwhelming the SDRAM with the needs of the display, and your needs to modify or paint the screen.

Limits apt to be 2047x1023, but don't see FHD or UHD to be achievable.

Do the math, find the bandwidth, find the pins.

[Robmar]

The clock is lower when RGB888 is used to interface to the LCD, right?  Talking with STM they think it might reach FHD at 30 FPS but are checking and have said they will get back to me.

In the meantime, it seems that the H723ZG (144pins) cannot be configured for LTDC RGB888 and 16-bit SDRAM, and it looks like 8-bit SDRAM will not handle the bandwidth needed for the SDRAM to be used as a frame buffer at 800x480 pixels (8BPP+CLUT).
STM have a $16 billion dollar turnover yet it's difficult for clients to get answers to straight-forward questions.  Perhaps an AI could be set-up to handle all the parts specifications and combinations so that clients could get accurate answers more quickly without having to learn all the datasheets.

So a simple question that maybe you could answer, as an STM expert: Can any STM MCU that operates >= 480 MHz with DSP, ideally FMAC, handle and 800x480 RGB888 LCD interface, using SDRAM as an external frame buffer (which probably needs 16-bit)?