STM32F0 Timer interrupt problem

[zenobik]

Posted on May 11, 2018 at 13:05

I'm using STM32F030R8 @ 40MHz and TIM6. I want to wait for some time without blocking main function, so i used TIM6 - code below:

TIM6->CR1 |= TIM_CR1_ARPE | TIM_CR1_OPM;//auto-reload, one-pulse

TIM6->PSC = 4000-1;//100usec

TIM6->ARR = 5000-1; //500ms for test

TIM6->DIER |= TIM_DIER_UIE; //enable update interrupt

NVIC_EnableIRQ(TIM6_IRQn);

EXTI interrupt turns on the timer (TIM6->CR1 |= TIM_CR1_CEN). But after the first EXTI interrupt, first timer update interrupt is executing after 130us instead of 500ms. After the first interrupt everything works properly - I get 500ms delay.

EXTI interrupt code:

void EXTI4_15_IRQHandler(void)

{

if(EXTI->PR & EXTI_PR_PR13)

{

TIM6->CR1 |= TIM_CR1_CEN;

GPIOA->BSRR = GPIO_BSRR_BS_5;

EXTI->PR |= EXTI_PR_PR13;

}

}

TIM6 interrupt code:

void TIM6_IRQHandler(void)

{

GPIOA->BSRR = GPIO_BSRR_BR_5;

TIM6->SR &= ~(TIM_SR_UIF);

}

Do you know what I'm doing wrong?

[Tesla DeLorean]

Posted on May 11, 2018 at 13:23

Well UPDATE is defines as CNT == 0, so yes will fire immediately.

Don't do this

TIM6->SR &= ~(TIM_SR_UIF);

The hardware is designed to clear like this without the hazard your RMW version induces.

TIM6->SR = ~(TIM_SR_UIF);

[henry.dick]

Posted on May 11, 2018 at 14:42

'

I get 500ms delay.'

if can be done so much more easily with a free-running timer, without any of the complexity involved here.

[Jan Waclawek]

Posted on May 11, 2018 at 17:44

TIMx_PSC is preloaded, i.e. the value you write does not get 'active' until the next update event. You can force an update by writing 1 to TIMx_EGR.UG, but then you'll to clear the update flag in SR to avoid immediate interrupt to fire.

I've participated in a related thread recently (there's a timing gotcha) and this comes up here regularly, try to search here.

JW

[waclawek.jan]

Posted on May 11, 2018 at 23:49

https://community.st.com/0D50X00009XkWWcSAN

[zenobik]

Posted on May 13, 2018 at 12:02

Thanks for advices. So, working code looks like that:

TIM6->ARR = 5000-1;

TIM6->CR1 |= TIM_CR1_CEN; //enable timer to generate update

TIM6->EGR = TIM_EGR_UG; //software generated update - to set ARR

TIM6->CR1 |= TIM_CR1_ARPE | TIM_CR1_OPM;//auto-reload, one-pulse

TIM6->DIER |= TIM_DIER_UIE; //enable update interrupt

TIM6->PSC = 4000-1;

TIM6->SR = ~(TIM_SR_UIF);

NVIC_EnableIRQ(TIM6_IRQn);

There are few instructions between setting EGR and celaring SR flag, so everything works fine.

henry.****

‌ - timerhave to be fired by EXTI interrupt. Free-running timer is useless in my case.