TIM4_ICInitStructure.TIM_Channel = TIM_Channel_3; //       
          TIM4_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Rising;       
          TIM4_ICInitStructure.TIM_ICSelection = TIM_ICSelection_DirectTI;
          TIM4_ICInitStructure.TIM_ICPrescaler = TIM_ICPSC_DIV1;         //配置输入分频,不分频
          TIM4_ICInitStructure.TIM_ICFilter = 0x00;//IC1F=0000
          TIM_ICInit(TIM4, &TIM4_ICInitStructure);
请问这个实现什么功能？
        TIM_ITConfig(TIM4,TIM_IT_Update|TIM_IT_CC3,ENABLE);
TIM_OC3PolarityConfig(TIM4,TIM_ICPolarity_Rising);
  TIM_ClearITPendingBit(TIM4, TIM_IT_CC3|TIM_IT_Update);
我就是这些通道分不清楚