STM32 timer settings changing

Question

I'm using an STM32F407VG. I created a 28 kHz square wave by using timer PWM generation. When I look at the oscilloscope, I can see it clearly. I'm having trouble changing the frequency of the PWM without stopping it.

I found two functions which are __HAL_TIM_SET_PRESCALER() and __HAL_TIM_SET_AUTORELOAD().

HAL_TIM_PWM_Start(&htim2, TIM_CHANNEL_1);
__HAL_TIM_SET_AUTORELOAD(&htim2,99);
__HAL_TIM_SET_PRESCALER(&htim2,29);

I set prescaler and autoreload in CubeMX. Prescaler is 2 and ARR is 999, but I want to change the prescaler to 29 and ARR to 99. I can see a square wave with HAL_TIM_PWM_Start(), but when I add 2 other functions it goes away. I commented those prescaler and ARR functions and I saw that PWM was working.

I don't know how to change the prescaler and ARR values without stopping the PWM.

Answer 1

I solved my problem today. I was changing ARR and Prescaler together. But i have seen a guy's comment which was about missing part of changing.

So i decided to change all of them at the same time.

__HAL_TIM_SET_AUTORELOAD();
__HAL_TIM_SET_PRESCALER();
__HAL_TIM_SET_COMPARE();

When i had done like this. It worked. I hope it will be helpful for anyone who faces the same struggle.

Answer 2

Let's say you update ARR as 90 when your CNT register is 95, when do you think the next update/reload happens?

Options:

when you set ARR check CNT if it's higher than next ARR value.(poor)

set CNT to 0 when you are updating ARR.(OK)

Enable relevant timer interrupt, update ARR only in timer overflow ISR.(Best in my opinion)