void TIM2_Cap_Init(u16 arr,u16 psc)
{

  GPIO_InitTypeDef GPIO_InitStructure;
  NVIC_InitTypeDef NVIC_InitStructure;
TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
  TIM_ICInitTypeDef  TIM_ICInitStructure;
  /* TIM2 clock enable */
  RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);

  /* GPIOA clock enable */
  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
  
  
  GPIO_InitStructure.GPIO_Pin =  GPIO_Pin_0;
  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_UP;
  GPIO_Init(GPIOA, &GPIO_InitStructure);
GPIO_SetBits(GPIOA,GPIO_Pin_0); //PA0 ??
  /* Connect TIM pins to AF2 */
  GPIO_PinAFConfig(GPIOA, GPIO_PinSource0, GPIO_AF_TIM2);
  
  //初始化定时器2

TIM_TimeBaseStructure.TIM_Period = arr; //设定计数器自动重装值 
TIM_TimeBaseStructure.TIM_Prescaler =psc; //预分频器   
TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1; //设置时钟分割:TDTS = Tck_tim
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;  //TIM向上计数模式
TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure); //根据TIM_TimeBaseInitStruct中指定的参数初始化TIMx的时间基数单位
   TIM_ICInitStructure.TIM_Channel = TIM_Channel_1;
  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(TIM2, &TIM_ICInitStructure);
  

  /* Enable the TIM2 global Interrupt */
  NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQn;
  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
  NVIC_Init(&NVIC_InitStructure);
    /* TIM enable counter */
TIM_ITConfig(TIM2,TIM_IT_Update|TIM_IT_CC1,ENABLE);//允许更新中断 ,允许CC1IE捕获中断

    TIM_Cmd(TIM2,ENABLE ); //使能定时器5
}

u8  TIM2CH1_CAPTURE_STA=0; //输入捕获状态    
u16 TIM2CH1_CAPTURE_VAL; //输入捕获值
 u16 t=0;
//定时器5中断服务程序  
void TIM2_IRQHandler(void)
{ 

if((TIM2CH1_CAPTURE_STA&0X80)==0)//??????
{  
if (TIM_GetITStatus(TIM2, TIM_IT_Update) != RESET)
 
{    
if(TIM2CH1_CAPTURE_STA&0X40)//?????????
{
if((TIM2CH1_CAPTURE_STA&0X3F)==0X3F)//??????
{
TIM2CH1_CAPTURE_STA|=0X80;//?????????
TIM2CH1_CAPTURE_VAL=0XFFFF;
}
else TIM2CH1_CAPTURE_STA++;
}  
}
if (TIM_GetITStatus(TIM2, TIM_IT_CC1) != RESET)//捕获1发生捕获事件
{
if(TIM2CH1_CAPTURE_STA&0X40) //捕获到一个下降沿
{  
t++;
TIM2CH1_CAPTURE_STA|=0X80; //标记成功捕获到一次上升沿
TIM2CH1_CAPTURE_VAL=TIM_GetCapture1(TIM2);
  TIM_OC1PolarityConfig(TIM2,TIM_ICPolarity_Falling); //CC1P=0 设置为上升沿捕获
}else   //还未开始,第一次捕获上升沿
{
TIM2CH1_CAPTURE_STA=0; //清空
TIM2CH1_CAPTURE_VAL=0;
TIM_SetCounter(TIM2,0);
TIM2CH1_CAPTURE_STA|=0X40; //标记捕获到了上升沿
  TIM_OC1PolarityConfig(TIM2,TIM_ICPolarity_Rising); //CC1P=1 设置为下降沿捕获
}    
}           
  }
 
    TIM_ClearITPendingBit(TIM2, TIM_IT_CC1|TIM_IT_Update); //清除中断标志位
 
}


int main(void)
{

    NVIC_Configuration(); //设置NVIC中断分组2:2位抢占优先级，2位响应优先级
uart_init(115200); //串口初始化为9600  
LED_Init();
// TIM_Config();

TIM3_PWM_Init(1999,83);
TIM_SetCompare1(TIM3,400);
TIM_SetCompare2(TIM3,800);
TIM_SetCompare3(TIM3,1200);
TIM_SetCompare4(TIM3,1600);
TIM2_Cap_Init(0XFFFF,83);
  while (1)
  {
if(TIM2CH1_CAPTURE_STA&0X80)//成功捕获到了一次上升沿
{
temp=TIM2CH1_CAPTURE_STA&0X3F;
temp*=65536;//溢出时间总和
temp+=TIM2CH1_CAPTURE_VAL;//得到总的高电平时间
printf("HIGH:%d us ",temp);//打印总的高点平时间
printf("Count:%d times ",t);
TIM2CH1_CAPTURE_STA=0;//开启下一次捕获
}
delay_ms(200);

  }
}

STM32F407输入捕获程序，参照原子的例程配置的，捕获低电平持续时间，但是测量的数值总是少了1us，请问下有谁知道是什么原因吗？