How to use DMA to change PWM frequency?

[Caraffa]

Hi! I know overall idea of DMA and i need to use it but i have no idea how to do it.

I found one post with same question but i didn't found any helpful info for me. I'm not advanced in case of using registers. I used them to directly change CCR and ARR sometimes, so I need a direct answer.

Edit: It is worth mentioning that I use CubeIDE

​

Thanks for help

[waclawek.jan]

Make TIMx_ARR to be the target of the DMA transfer on the peripheral side. Make sure ARR preload is switched on.

JW

[Caraffa]

Could you explain it further, especially first part? How i can make TIMx_ARR target of the DMA transfer? ​

[waclawek.jan]

You write it in the Peripheral address register of DMA channel/stream, while the channel/stream is set to transfer memory-to-peripheral.

Read the DMA chapter first. You may also want to read the Timer cookbook AN4776. And next time start with stating which STM32 are you using.

JW

[Caraffa]

I'm using stm32f407g

[Javier1]

I use here a DMA(triggered with a timer)---->PWM(timer) to create a neopixel LED driver, maybe you can fish something out, specially the DMA+PWMtest.

The mcu shouldnt matter as long as you have DMA and TIM available to use.

I tested this with stm32f103 and stm32f7

[Caraffa]

You use HAL_TIM_PWM_Start_DMA function but if i understand it correctly, it can access only TIMx_CCRx registry but i need TIMx_ARR

[Javier1]

what if you try this inside HAL_TIM_PWM_Start_DMA()

//instead of this:
 if (HAL_DMA_Start_IT(htim->hdma[TIM_DMA_ID_CC1], (uint32_t)pData, (uint32_t)&htim->Instance->CCR1, Length) != HAL_OK)
 {
 
//do this :
 
 if (HAL_DMA_Start_IT(htim->hdma[TIM_DMA_ID_CC1], (uint32_t)pData, (uint32_t)&htim->Instance->ARR, Length) != HAL_OK)
 {

[Caraffa]

It turned out that i don't need DMA at all. I thought I needed because weird things were happening when i was updating ARR directly with TIMx->ARR = y. It turned out that I was doing that when counter was waaay beyond my y value. I just added line to reset CNT value and everything works like a charm.

[waclawek.jan]

Look at my first reply:

> Make sure ARR preload is switched on.

Read the TIM chapter. ARR preload is switched on by setting TIMx_CR1.ARPE.

JW