求助：在论坛上参考了好像是战舰版的示例程序，可以用定时器输入捕获的方式计算方波的高电平时间，于是在那个程序的基础上做了些修改，想要套用在计算正弦波的周期上，但是计算出的周期不正确，下面贴出来部分程序：请大家帮忙分析分析问题，谢谢

void TIM3_Cap_Init(u16 arr,u16 psc)
{  
    TIM_ICInitTypeDef  TIM3_ICInitStructure;
    GPIO_InitTypeDef GPIO_InitStructure;
    TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
    NVIC_InitTypeDef NVIC_InitStructure;

    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE); 
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE); 

    GPIO_InitStructure.GPIO_Pin  = GPIO_Pin_7;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPD; 
    GPIO_Init(GPIOA, &GPIO_InitStructure);
    GPIO_ResetBits(GPIOA,GPIO_Pin_7);

    TIM_TimeBaseStructure.TIM_Period = arr; 
    TIM_TimeBaseStructure.TIM_Prescaler =psc;
    TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1; 
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);
  
    TIM3_ICInitStructure.TIM_Channel = TIM_Channel_2; 


    TIM3_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Rising;
    TIM3_ICInitStructure.TIM_ICSelection = TIM_ICSelection_DirectTI; 
    TIM3_ICInitStructure.TIM_ICPrescaler = TIM_ICPSC_DIV1;
    TIM3_ICInitStructure.TIM_ICFilter = 0x00;
    TIM_ICInit(TIM3, &TIM3_ICInitStructure);

    TIM_ITConfig(TIM3,TIM_IT_Update|TIM_IT_CC2,ENABLE);
    TIM_Cmd(TIM3,ENABLE );

    NVIC_InitStructure.NVIC_IRQChannel = TIM3_IRQn; 
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 2; 
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0; 
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; 
    NVIC_Init(&NVIC_InitStructure); 
}

void TIM3_IRQHandler(void)
{ 
   TIM3CH2_CAPTURE_VAL=TIM_GetCapture2(TIM3);
   TIM_ClearITPendingBit(TIM3, TIM_IT_CC2|TIM_IT_Update);
   TIM3CH2_CAPTURE_VAL = 0;
}