EXIT的步骤

涉及到 NVIC,GPIO,EXIT,AFIO 四个外设

RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA|RCC_APB2Periph_AFIO,ENABLE);
	NVIC_InitTypeDef NCIC_InitStructure;
	NVIC_PriorityGroupConfig(NVIC_PriorityGroup_1);
	NCIC_InitStructure.NVIC_IRQChannel=EXTI0_IRQn;
	NCIC_InitStructure.NVIC_IRQChannelCmd=ENABLE;
	NCIC_InitStructure.NVIC_IRQChannelPreemptionPriority=1;
	NCIC_InitStructure.NVIC_IRQChannelSubPriority=1;
	NVIC_Init(&NCIC_InitStructure);
```

	
	GPIO_EXTILineConfig(GPIO_PortSourceGPIOA,GPIO_PinSource0);
	//RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA|RCC_APB2Periph_AFIO,ENABLE);
	GPIO_InitTypeDef GPIO_InitStructure;
	GPIO_InitStructure.GPIO_Mode=GPIO_Mode_IN_FLOATING;
	GPIO_InitStructure.GPIO_Pin=GPIO_Pin_0;
	//GPIO_InitStructure.GPIO_Speed=GPIO_Speed_50MHz;	
	GPIO_Init(GPIOA,&GPIO_InitStructure);
	
	EXTI_InitTypeDef EXTI_InitStructure;
	EXTI_InitStructure.EXTI_Line=EXTI_Line0;
	EXTI_InitStructure.EXTI_LineCmd=ENABLE;
	EXTI_InitStructure.EXTI_Mode=EXTI_Mode_Interrupt;
	EXTI_InitStructure.EXTI_Trigger=EXTI_Trigger_Rising;
	EXTI_Init(&EXTI_InitStructure);`
```
void EXTI0_IRQHandler(void)
{
  //确保是否产生了EXTI Line中断
	if(EXTI_GetITStatus(EXTI_Line0) != RESET) 
	{
		Led_Toggle();// LED1 取反		
		
    //清除中断标志位
		EXTI_ClearITPendingBit(EXTI_Line0);     
	}  
}
```