#include "stm32f4xx.h"

int main ()  {

  RCC->AHB1ENR |= 0x0011;       // Enable clock for GPIOE & GPIOA
  RCC->APB1ENR |= 0x00000008;   // Enable Clock for Timer 5
  
  GPIOE->MODER |= 0x00010000;   // Output pin for time mark at port E
  GPIOA->MODER |= 0x00001000;   // output pin for LED D390
  
  NVIC_EnableIRQ(TIM5_IRQn);    // Enable IRQ for TIM5 in NVIC

  TIM5->ARR     = 84000;        // Auto Reload Register value => 1ms
  TIM5->DIER   |= 0x0001;       // DMA/IRQ Enable Register - enable IRQ on update
  TIM5->CR1    |= 0x0001;       // Enable Counting

  while (1) {
    if (GPIOE->IDR & 0x01) GPIOA->ODR |=  0x0040;   // press S370 to turn on D390
    else                   GPIOA->ODR &= ~0x0040;
  };
}

void TIM5_IRQHandler(void)
{
  TIM5->SR &= ~0x00000001;      // clear IRQ flag in TIM5
  GPIOE->ODR |=  0x0100;        // PE08 up
  GPIOE->ODR &= ~0x0100;        // PE08 down
}