输入捕获进入中断不准确

tiM1的通道1捕获
#include<STM32f10x_lib.h>
#include "delay.h"
#include "sys.h"
void TIM1_CC_IRQHandler(){
GPIOE->ODR|=0x00000001;//指示灯亮
TIM1->SR&=~(1<<1);//清除捕获/比较1事件中断标志位
}
void Timerx_Init(u16 arr,u16 psc){//输入捕获
RCC->APB2ENR|=1<<(2+0);
GPIOA->CRH&=0xFFFFFFF0;
GPIOA->CRH|=0x00000004;
GPIOA->ODR|=0x00000100;
RCC->APB2ENR|=1<<11;//TIM1定时器时钟开启
TIM1->ARR=arr;
TIM1->SC=psc;
TIM1->CCMR1&=0xFFFC;
TIM1->CCMR1|=0x0001;//CC1通道配置为输入，IC1映射到IT1上
TIM1->CCMR1&=0xFF0F;
TIM1->CCMR1|=0x0030;//fsampling=fck_int,N=8
TIM1->CCER&=~(1<<1);//上升沿有效
TIM1->CCMR1&=0xFFF3;//无预分频器，上升沿时产生捕获
TIM1->CCER|=1<<0;//捕获使能
TIM1->DIER|=1<<1;// 使能中断
TIM1->CR1|=1<<0;//计数器使能
riorityGroup_Config(2);
riority_Config(1,3,TIM1_CC_IRQChannel,2);
}
void GPIO_Config(){
RCC->APB2ENR|=1<<(2+4);
GPIOE->CRL&=0xFFFFFFF0;
GPIOE->CRL|=0x00000003;
GPIOE->ODR&=0x00000000;//初始化指示灯灭
}
int main(){
Stm32_Clock_Init(9);
delay_init(72);
GPIO_Config();
Timerx_Init(65535,65535);
while(1);
}
发现复位就进中断了
如果把PA8口先拉高，然后拉低有时可以进中断，有时要等下才进中断？这是怎么回事？