RNG clock messing up LTDC

troy1818 · ‎2016-04-24

Posted on April 24, 2016 at 14:02

Hi,

I have configured my stm32f756xx mcu to run LTDC. Everything works fine. However when I activate the RNG clock like so:

__HAL_RCC_RNG_CLK_ENABLE();

I seem to get a myriad of red pixels (static snow) on the screen (whole screen, not only the window that I have configured, see attachment). This is problem in silicon perhaps? or the hal library ?

I am using HAL library V1.0.3.

Regards,

Rygelxvi

AndyJT · ‎2016-04-25

Posted on April 25, 2016 at 19:04

When enabling the RNG clock, are you also changing anything to do with the PLLSAI? It sounds like the new clock setup is changing the LTDC pixel clock coming from PLLSAI1...

Amel NASRI · ‎2016-04-26

Posted on April 26, 2016 at 12:20

Hi rygelxvi,

I cannot reproduce the issue with the example STM32Cube_FW_F7_V1.3.0\Projects\STM32746G-Discovery\Examples\LTDC\LTDC_Display_1Layer.

Is it possible for you to try the same example and let us know if you face a problem when you add code to enable the RNG clock?

Please note that last HAL drivers version is 1.0.4 available in STM32CubeF7 V1.3.0.

-Mayla-

To give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

troy1818 · ‎2016-04-29

Posted on April 29, 2016 at 09:40

Hi,

Thanks for answering.

I am not doing anything other than the one line that I wrote in my last comment (activating clock for RNG).

@Mayla

In a couple of days I will take a deeper look at this and come back to you.

Regards,

Rygelxvi

troy1818 · ‎2016-06-13

Posted on June 13, 2016 at 22:42

Hi again,

I just checked this issue. It seems that if you configure ltdc wrong, where you choose GPIO_AF14_LTDC for the pins PB0 and PB1 where it should have been GPIO_AF9_LTDC (4 ltdc pins use 9 instead of 14) AND you turn on the clock for RND, then you will get the problem I shown in this thread.

After I corrected my code to use AF9 I cannot reproduce the problem and I can have RND clock on all the time :)

Regards,

Rygelxvi