Weird Jitter when using DMA to generate PWM in GPIOs

[Okbit]

So i was trying to generate pwm on all gpio pins of a stm32F103 for my application. I found followed this guide:https://www.hackster.io/javier-munoz-saez/all-pins-as-pwm-at-the-same-time-baremetal-stm32-1df86f

the essence is using the function:

 

 

 

 

void setSoftPWM(uint16_t pin, uint32_t duty ,uint32_t *softpwmbuffer){
	for (uint32_t i = 0; i < lengthSoftPWMbuffer; ++ i) {
		if(i<duty){//set pin
			softpwmbuffer[i]&=(uint32_t)~(pin<<16);
			softpwmbuffer[i]|=(uint32_t)pin;
		}else{//reset pin
			softpwmbuffer[i]&=(uint32_t)~(pin);
			softpwmbuffer[i]|=(uint32_t)pin<<16;
		}
	}

}

 

 

 

 

 to generate a buffer array of 100 elements which contain the gpio info for the GPIOX_BSRR register depending on the duty cycle. I configure the dma in circular mode and trigger it with a timer update event.

I do the initial configuration using CubeMX and then add the following code to start the dma.

 

 

 

 

HAL_TIM_Base_Start(&htim1);
 HAL_TIM_Base_Start(&htim2);
 HAL_TIM_Base_Start(&htim4);
 HAL_DMA_Start_IT(&hdma_tim1_up, 	(uint32_t)&(dataA[0]), (uint32_t)&(GPIOA->BSRR), sizeof(dataA));
 HAL_DMA_Start_IT(&hdma_tim2_up, 	(uint32_t)&(dataB[0]), (uint32_t)&(GPIOB->ODR), sizeof(dataB));
 HAL_DMA_Start_IT(&hdma_tim4_up, 	(uint32_t)&(dataC[0]), (uint32_t)&(GPIOC->BSRR), sizeof(dataC));

 //start DMAs
 __HAL_TIM_ENABLE_DMA(&htim1, TIM_DMA_UPDATE);
 __HAL_TIM_ENABLE_DMA(&htim2, TIM_DMA_UPDATE);
 __HAL_TIM_ENABLE_DMA(&htim4, TIM_DMA_UPDATE);

 

 

 

 

 Then i use the setSoftPWM() function to initialize a pwm in different gpio pins like so:

 

 

 

 

setSoftPWM(GPIO_PIN_0, 90, (uint32_t*)&dataA); //sets gpioA
setSoftPWM(GPIO_PIN_0, 40, (uint32_t*)&dataB); //sets gpioB
setSoftPWM(GPIO_PIN_13, 60, (uint32_t*)&dataC);//sets gpioC

 

 

 

 

 

 

But when i upload to the MCU i am getting these waveforms on the pins:

 

PWM at 100% duty cycle

 

 

PWM at 0% duty cycle

 

 

PWM at 50% duty cycle:

 

 

as you can see the pwm is working somewhat but only in a very small part of the waveform. The rest of the waveform has this weird jitter.

I tried a bunch of things but am unable to eliminate the jitter. The random waveforms are completely arbitrary and change with the gpio ports and everytime i reset the MCU.

 

At first i thought maybe it is a hardware problem so i tried it in a different f103 and a L432kc but am getting the same result.

So its probably a software problem but no matter what i try, cant really explain or eliminate the jitter.

what am i missing here?

 

Regards:

Okbit

 

Here is the full code made using stm32CubeIDE

[Sarra.S]

Hello @Okbit, welcome to ST Community, 

I'd highly recommend referring to the TIM example under the STM32CubeF1

The example titled "TIM_DMA" describes how to use DMA with TIMER Update request to transfer Data from memory to TIMER Capture Compare Register. The objective of the example is to configure TIM1 channel 3 to generate a complementary PWM signal. You may take this example as a reference to correctly configure your peripheral.

[Okbit]

Thats a great resource that i wasn't aware of thanks for the info

 

[TDK]

> sizeof(dataA)

The function wants the number of transfers, not the number of bytes.

This should be sizeof(dataA) / sizeof(*dataA), or however else you want to write it such that it's the number of uint32_t values in the buffer.

[Okbit]

That was it! I never realized it was that simple!

Thank you so much i was stuck on this problem forever.