How to limit TouchGFX to 30 fps

[nico23]

I'm using an STM32H7S78-DK with TouchGFX and FreeRTOS. I would like to limit the framerate of the target to 30fps but withouth reducing the LTDC frequency.

Basically having the VSYNC fired at 30fps

I've already set the 

    ((touchgfx::HALSDL2*)&hal)->setVsyncInterval(33.333);

In the simulator

Is there a way to force it on the target?

[unsigned_char_array]

Increase your porch sizes.

[nico23]

what? Would you be more precise

[unsigned_char_array · Accepted solution]

You can increase the front and back porches in your LTDC. 
This way you use more clock cycles per frame so your frame rate drops.

[nico23]

Hi @unsigned_char_array 

Thanks a lot for the answer. My goal in reducing the refresh rate was to save CPU cycles for other operations; with the approach you propose, it feels like I'm just burning CPU cycles to drop the FPS, without really removing work to process the frame, or am I wrong?

Studying a bit, I've found out that another way is to use a custom timer set to 30Hz and toggle the VSYNC pin, but I think that's way more tricky than changing parameters in CubeMX

[unsigned_char_array]

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@nico23 wrote:

Hi @unsigned_char_array 

Thanks a lot for the answer. My goal in reducing the refresh rate was to save CPU cycles for other operations; with the approach you propose, it feels like I'm just burning CPU cycles to drop the FPS, without really removing work to process the frame, or am I wrong?

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 The CPU is not busy waiting (blocking) for LTDC interrupts. You'll actually get more idle time per frame.

https://support.touchgfx.com/docs/development/touchgfx-hal-development/scenarios/scenarios-measure-performance#performance-metrics