#include "stm32f4xx_conf.h"

static uint32_t messwert=0;
static float frequenz=0;

void init(void)
{
  GPIO_InitTypeDef GPIO_InitStructure;
  TIM_ICInitTypeDef TIM_ICInitStructure;
  NVIC_InitTypeDef NVIC_InitStructure;
  TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;

  // Clock Enable
  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOC, ENABLE);

  // Clock enable
  RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);

  // Config des Pins als AF-Input
  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
  GPIO_Init(GPIOC, &GPIO_InitStructure);

  // Alternative-Funktion mit dem IO-Pin verbinden
  GPIO_PinAFConfig(GPIOC, GPIO_PinSource9, GPIO_AF_TIM3);

  TIM_TimeBaseStructure.TIM_Period = 65535;
  TIM_TimeBaseStructure.TIM_Prescaler = 0;
  TIM_TimeBaseStructure.TIM_ClockDivision = 0;
  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
  TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;
  TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);

  // Vorteiler einstellen (83 => 1MHz)
  TIM_PrescalerConfig(TIM3, 1, TIM_PSCReloadMode_Immediate);

  // Channel 4
  TIM_ICInitStructure.TIM_Channel = TIM_Channel_4;
  TIM_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Falling;
  TIM_ICInitStructure.TIM_ICSelection = TIM_ICSelection_DirectTI;
  TIM_ICInitStructure.TIM_ICPrescaler = TIM_ICPSC_DIV1;
  TIM_ICInitStructure.TIM_ICFilter = 0x0;
  TIM_ICInit(TIM3, &TIM_ICInitStructure);

  // Timer enable
  TIM_Cmd(TIM3, ENABLE);

  NVIC_InitStructure.NVIC_IRQChannel = TIM3_IRQn;
  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
  NVIC_Init(&NVIC_InitStructure);

  TIM_ITConfig(TIM3, TIM_IT_CC4, ENABLE);
}

void TIM3_IRQHandler(void)
{
  static uint16_t pos=0;
  static uint32_t t1=0;
  static uint32_t t2=0;


  if(TIM_GetITStatus(TIM3, TIM_IT_CC4) == SET) {
    // Interrupt Flags loeschen
    TIM_ClearITPendingBit(TIM3, TIM_IT_CC4);

    if(pos==0) {
      pos=1;
      t1=TIM_GetCapture4(TIM3);
    }
    else {
      t2=TIM_GetCapture4(TIM3);

      if(t2>=t1) {
        messwert=t2-t1;

      }
      else {
        messwert=(0xFFFF - t1) + t2;
      }
      t1 = t2;
    }
  }
}

int main(void)
{
	init();
	SystemInit();

    while(1)
    {
    	frequenz = 42000000/messwert;
    }
}