Undesired Square Wave on Pin configured as GPIO_Output used for SPI Slave Select

[SMano.1]

I have a STM32G0B0KET6. I have configured Pin A4 as a GPIO Output. However, I see a 506.000 Hz Square Wave instead of it being high.

It sometimes works correctly as a slave select. At one point the line goes to 0V. If I reset the controller after this, I now see the Square Wave on the Pin. The rest of the controller functionality works fine.

[SMano.1]

It sometimes works correctly as a slave select. However, at one point the line goes low. When it's low, if I reset the controller, I then see a Square Wave with a frequency of 506.000 Hz. I have no idea why this is happening. I have tried configuring the pin as an input and the same thing happens.

[Tesla DeLorean]

Is this on some board? What exactly are we dealing with here?

512 Hz might be an RTC test thing, but not something ringing any bells currently.

[TDK]

PA4 is an RTC_OUT1 which allows output of a 512Hz signal. I believe this feature supersedes whatever you have set up in the GPIOx registers. Examine the relevant RTC registers.

[SMano.1]

I enabled RTC_OUT1, and saw the exact same 506.00 Hz Square Wave. Now I just need to figure out why the pin changes mode on reset.

[waclawek.jan]

Cube/HAL? Maybe uninitialized field in init-struct when initializing RTC.

JW

[SMano.1]

I came up with a workaround for my application. I am not using the RTC, do I did a DeInit on it.

	if(hrtc.Instance->CR&(1<<23))
	{
		HAL_RTC_DeInit(&hrtc);
	}

I added this code in the loop that uses the pin.