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TIMER 3 Interrupt

Question asked by sanjay kumawat on Apr 25, 2018
Latest reply on May 2, 2018 by sanjay kumawat

Hi all,

This is a question regarding STM32F0 TIM3.

I have written this code in keil compiler

/***** main.c*****/

void GPIO_Init(void); 
void TIM3_Init(void);

int main()
 GPIO_Init();         // Intializing PA5


void GPIO_Init()

 // Enable clock for GPIOA
 RCC->AHBENR |= (1<<17);
 //Configuration of PA5
 GPIOA->MODER |= (1<<10);             // PA5 as general purpose output mode
 GPIOA->OTYPER &= ~(1<<5);            // PA5 as output push pull
 GPIOA->OSPEEDR |= ((1<<10)|(1<<11)); // PA5 at high speed
 GPIOA->PUPDR &= ~((1<<10)|(1<<11));  // PA5 as no pull-up, pull-down
 GPIOA->ODR = 0;            // PA5 as Output Low

void TIM3_Init()
 RCC->APB1ENR |= (1<<1);        // Enable clock for TIM3
 TIM3->PSC = 999;           // Int clk divided by 1000(999+1)
 TIM3->ARR = 7999;           // Counts from 0 to 7999
 TIM3->DIER = 1;            // Update interrupt enable
 __NVIC_SetPriority(TIM3_IRQn, 0);   // Set TIM3 interrupt vector priority to 0
 __NVIC_EnableIRQ(TIM3_IRQn);     // Enable TIM3 interrupt vector
 TIM3->CR1 = 1;            // Enable TIM3 counter

void ISR()
   TIM3->SR = 0;
   GPIOA->ODR ^= (1<<5);      // Toggle PA5 Output




/**** it.c*****/

void ISR(void);

void TIM3_IRQHandler(void)


Here system clock freq and timer clock freq is 8Mhz(internal oscillator).

when I run this code I found that my led on PA5 toggles per second that should be as per code.

But there is an problem in output that when microcontroller is done reset by a reset button the PA5 Is immediately high and then toggles @ per second i.e. the tim3 generate a update interrupt when it is enabled. I want that first interrupt should come after timer completion means 1 sec. so that when I reset the microcontroller output can be at low and after 1 sec it toggles( goes high)  and so on.


"My question is why microcontroller is making High to the UIF bit TIM3->SR reg. when TIM3 counting is enabled. I think it should be after timer completion".waclawek.janNesrine M