void TIM2_Handler(void)
{    TIM2->SR &=~ TIM_SR_UIF;
    GPIOA->BSRR =GPIO_BSRR_BS3;
       GPIOA->BSRR =GPIO_BSRR_BR3;  
}


int main(void)
{
        
  RCC->APB2ENR    |= RCC_APB2ENR_IOPAEN;
  GPIOA->CRL    &= ~GPIO_CRL_CNF3;
  GPIOA->CRL   |= GPIO_CRL_MODE3_0;    

  GPIOA->CRL    &= ~GPIO_CRL_CNF2;
  GPIOA->CRL   |= GPIO_CRL_MODE2_0;    
      
          RCC->APB1ENR |= RCC_APB1ENR_TIM2EN;
        
        TIM2->PSC=2;
        TIM2->ARR=60;
        TIM2->DIER |= TIM_DIER_UIE;
        TIM2->CR1  |= (TIM_CR1_CEN | TIM_CR1_ARPE);
        
        
         NVIC_EnableIRQ (TIM2_IRQn);
         TIM2->SR &=~ TIM_SR_UIF;
      __enable_irq ();


         while(1)
    {
               
        GPIOA->BSRR =GPIO_BSRR_BS2
        GPIOA->BSRR =GPIO_BSRR_BR2;    
          
    }

}