Phase shift with swapping polarity

[RLD]

Hi
I am working on a STM32G484QET6 uC. On a timer I have configured two output channels with Output Compare Toggle Mode. So that I get a quadrature signal.
When configuring the first value, everything works perfectly. The duty cycle is 50% and the phase shift is 90 degrees to each other.
But in my application I have to change the frequency during the run, means also the CCR value to keep the 50% duty cycle. When I update the values, I stop the timer and then, after updating I restart it. Now I have the problem that the polarity is sometimes swapping after changing the values. For example, the channel 1 signal is behind channel 2 and I want it the other way around.
How do I change the values so that this doesn't happen?

Thank you!
RLD

[RLD]

Addition: The pulse for changing the frequency is triggered by a button via interrupt. So there is not much to do in terms of the timing of the change in frequency and timer values.

[Sarra.S]

Hello @RLD, welcome to ST Community, 

I think the right sequence will be 

1. Stop the timer 

2. Update CCR values 

3. Generate an update event (set UG bit in the TIMx_EGR register) to make sure that the new CCR values are loaded correctly 

4. Restart the timer 

Would you give it a try and let me know how it went? 

 

[RLD]

Hello @Sarra.S

Sadly, it still doesn't work. The polarity of the phase shift still sometimes changes after calling up the function to change the frequency.

Here is my function, if that might help:

 

void UpdateTimerFrequencyPhaseShift(uint16_t frequency, double phaseShift)
{
	uint32_t psc = 1;
	uint32_t arr;

	//================================================================
	//Calculate optimal prescaler and auto reload register for given new frequency (irrelevant for my problem)
	while(psc < 2 * MCU_CLK / 0x10000){
		arr = MCU_CLK / psc / frequency;
		if(arr <= 0x10000){
			psc--;
			arr--;

			break;
		}
		psc *= 2;
		}
	//================================================================
 HAL_TIM_OC_Stop(&htim1, TIM_CHANNEL_1);
 HAL_TIM_OC_Stop(&htim1, TIM_CHANNEL_2);

	TIM1->PSC = psc;
	TIM1->ARR = arr/2;
	TIM1->CCR2 = 1 + (arr*(phaseShift/360));

	TIM1->EGR |= TIM_EGR_UG;

	HAL_TIM_OC_Start(&htim1, TIM_CHANNEL_1);
	HAL_TIM_OC_Start(&htim1, TIM_CHANNEL_2);
}

 

The frequency, the phase shift and the 50% duty cycle work perfectly, it's just this problem with the polarity swapping.

Thank You!

RLD

 

 

 

 

[waclawek.jan]

TIM1->EGR |= TIM_EGR_UG;

Don't.

JW

[RLD]

Thank You!

It works now, generating the update event was not necessary.
I have now solved it with activating the register preload feature.

RLD