STM32F4 TIM4 第二通道 配置成输入捕获，但已经进不了中断，求助。
TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
  TIM_ICInitTypeDef  TIM4_ICInitStructure;
GPIO_InitTypeDef GPIO_InitStructure;
uint16_t PrescalerValue = 0;
  NVIC_InitTypeDef NVIC_InitStructure;

  RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM4, ENABLE);
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD,ENABLE);

GPIO_InitStructure.GPIO_Pin  = GPIO_Pin_13;  
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz; //????100MHz
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP; //???ì????????
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP; //????
GPIO_Init(GPIOD, &GPIO_InitStructure);
//GPIO_ResetBits(GPIOD,GPIO_Pin_13);

GPIO_PinAFConfig(GPIOD, GPIO_PinSource13, GPIO_AF_TIM4);
  /* Time base configuration */
  TIM_TimeBaseStructure.TIM_Period = 65535;   //?????÷
  TIM_TimeBaseStructure.TIM_Prescaler = 0;  //???±??·????ó?????????÷
  TIM_TimeBaseStructure.TIM_ClockDivision = 0;
  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Down;
  TIM_TimeBaseInit(TIM4, &TIM_TimeBaseStructure);

TIM_ARRPreloadConfig(TIM4,ENABLE);   //????×???×°??

  TIM4_ICInitStructure.TIM_Channel = TIM_Channel_2; //CC1S=01 ????
  TIM4_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Falling; //??????????
  TIM4_ICInitStructure.TIM_ICSelection = TIM_ICSelection_DirectTI; //??????TI1????????
  TIM4_ICInitStructure.TIM_ICPrescaler = TIM_ICPSC_DIV1; //??????????·???
  TIM4_ICInitStructure.TIM_ICFilter = 0x00;//IC1F=0000???????????¨?÷?????¨
  TIM_ICInit(TIM4, &TIM4_ICInitStructure);

  /* Enable the TIM3 gloabal Interrupt */
  NVIC_InitStructure.NVIC_IRQChannel = TIM4_IRQn;
  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0x0;
  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0x0;
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
  NVIC_Init(&NVIC_InitStructure);
   
  /* TIM Interrupts enable */
//  TIM_ITConfig(TIM4, TIM_IT_Update, ENABLE);
TIM_ITConfig(TIM4, TIM_IT_CC2, ENABLE);

  /* TIM3 enable counter */
  TIM_Cmd(TIM4, ENABLE);