Tearing Effect signal

[Ricko]

Hi,

we are planning to use the display shown in the attached datasheet.

It is MIPI-DSI and also has a Tearing Effect Output signal. How is the Tearing Effect signal connected to the micro? I could not find any dedicated pin but from reading online about that signal, it looks like it is for syncronization which makes me think that is needs to be very high speed (MIPI-DSI speed?) and no latency. But there is no such pin on any of the micros we looked at.

Does that signal need to be connected to a specific pin?

If so, which one?

Thank you

[GaetanGodart]

Hello @Ricko ,

You do not need a specific pin for the tearing effect, a general gpio is enough. it is because the screen will update every 16.6 ms, so the latency of the tearing effect will have little to no effect on the refresh rate.

I hope this helps!
If this comment answers your question, I invite you to select it as "best answer".

Regards,

[Ricko]

Thank you @GaetanGodart 

then it is not clear how the display that is updated directly and automatically from the DMA is going to synch with the tearing signal.

Could you please explain.

Thank you :)

[GaetanGodart]

Hello @Ricko ,

To prevent tearing, you can use the pin called DSIHOST_TE in STM32CubeMX:

This pin is setup when you enable the DSI host in STM32CubeMX. This is the pin you should connect to your screen to prevent tearing.

However, if you want to measure performances, you can look at the pin VSYNC-FREQ that you have to manually set :

Regards,

[GaetanGodart · Accepted solution]

Hello @Ricko ,

Have you been able to move forward with your project?

If you run in video mode , you can just control your screen as a LTDC.
If you run in command mode you need the tearing effect to prevent changing the framebuffer while you are updating the screen.
But I can't figure out if your display have an integrated memory.

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then it is not clear how the display that is updated directly and automatically from the DMA is going to synch with the tearing signal. :)

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I don't understand why the display is directly and automatically updated from the DMA.
However, the tearing effect prevent the screen from being updated while the framebuffer is being updated.

You board has a Tearing Effect Output, you can use that to tell TouchGFX when it is safe to update the framebuffer.

Regards,

[Ricko]

Hi @GaetanGodart 

thank you for following up on this.

That does also help on what I was looking into.

I am now waiting from some clarifications from the display manufacturer and depending on their feedback I will either ask you further clarification or close the ticket with your answer as the solution.

Thank you

[GaetanGodart]

Thank you for keeping us updated! :smiling_face_with_smiling_eyes:

Sure, don't hesitate if it is not clear!

Regards,

[GaetanGodart]

Hello @Ricko ,

Have you been able to move forward with your question?

Regards,

[Ricko]

Hi @GaetanGodart 

still doing some research because I had to prioritise other parts of the PCB design. I do have other questions related to this, but will open a new ticket once I have read more about them if I don't find an explanation somewhere else.

Thank you for your help and for following up on this.

Have a great weekend. :)

[Ricko]

Forgot to select your reply as solution. Done now. :)