我的程序是下面这么写的，PE2,PE3,PE4，PA0连接的按键都是正常工作，但是一复位或者关掉电源重启PA0（wk_up）引脚的按键就不起作用了，这是为什么啊？？

void exti_init(void)
{
        key_init();
       
        /*开启AFIO时钟*/
        RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO,ENABLE);
       
        /*声明EXTI和NVIC结构体*/
        EXTI_InitTypeDef EXTI_InitStructure;
        NVIC_InitTypeDef NVIC_InitStructure;
       
        GPIO_EXTILineConfig(GPIO_PortSourceGPIOE,GPIO_PinSource2);        //将GPIOE的Pin2映射到中断线
       
       
        /*编写中断服务函数*/
        EXTI_InitStructure.EXTI_Line = EXTI_Line2;
        EXTI_InitStructure.EXTI_LineCmd = ENABLE;
        EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt;
        EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Falling;
       
        EXTI_Init(&EXTI_InitStructure);
       
       
       
        GPIO_EXTILineConfig(GPIO_PortSourceGPIOE,GPIO_PinSource3);
       
        EXTI_InitStructure.EXTI_Line = EXTI_Line3;
       
        EXTI_Init(&EXTI_InitStructure);
       
       
       
        GPIO_EXTILineConfig(GPIO_PortSourceGPIOE,GPIO_PinSource4);
       
        EXTI_InitStructure.EXTI_Line = EXTI_Line4;
       
        EXTI_Init(&EXTI_InitStructure);
       
       
        GPIO_EXTILineConfig(GPIO_PortSourceGPIOA,GPIO_PinSource0);
       
        EXTI_InitStructure.EXTI_Line = EXTI_Line0;
        EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Rising;
        EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt;
       
        EXTI_Init(&EXTI_InitStructure);
       
        NVIC_InitStructure.NVIC_IRQChannel = EXTI0_IRQn;
        NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
        NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority =0x02;
        NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0x03;
       
        NVIC_Init(&NVIC_InitStructure);
       
        NVIC_InitStructure.NVIC_IRQChannel = EXTI2_IRQn;
        NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
        NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority =0x02;
        NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0x00;
       
        NVIC_Init(&NVIC_InitStructure);
       
        NVIC_InitStructure.NVIC_IRQChannel = EXTI3_IRQn;
        NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
        NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0x02;
        NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0x01;
       
        NVIC_Init(&NVIC_InitStructure);
       
        NVIC_InitStructure.NVIC_IRQChannel = EXTI4_IRQn;
        NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
        NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0x02;
        NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0x02;
       
        NVIC_Init(&NVIC_InitStructure);
}
/*EXTI2中断处理函数*/
void EXTI0_IRQHandler(void)
{
        delay_ms(10);
        if(key_up==1)
        {
                BEEP=!BEEP;
        }
        EXTI_ClearITPendingBit(EXTI_Line0);
}

void EXTI2_IRQHandler(void)
{
        delay_ms(10);
        //if(EXTI_GetITStatus(EXTI_Line2)!=RESET)
        if(key1==0)
        {
                LED0=!LED0;
        }
        EXTI_ClearITPendingBit(EXTI_Line2);
}

void EXTI3_IRQHandler(void)
{
        delay_ms(10);
        if(key2==0)
        {
                LED1=!LED1;
        }
        EXTI_ClearITPendingBit(EXTI_Line3);
}

void EXTI4_IRQHandler(void)
{
        delay_ms(10);
        if(key3==0)
        {
                LED0=!LED0;
                LED1=!LED1;
        }
        EXTI_ClearITPendingBit(EXTI_Line4);        //清除标志位
}