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void EXTI_Config(){
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    GPIO_InitTypeDef GPIO_InitStructure;
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    EXTI_InitTypeDef EXTI_InitStructure;
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    NVIC_InitTypeDef NVIC_InitStructure;
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    // 配置 PA1
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    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
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    GPIO_InitStructure.GPIO_Mode  = GPIO_Mode_IPU;
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    GPIO_InitStructure.GPIO_Pin   = GPIO_Pin_1;
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    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
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    GPIO_Init(GPIOA, &GPIO_InitStructure);
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    RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO, ENABLE);
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    // Line1 中断线使用来自 GPIOA 的信号
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    GPIO_EXTILineConfig(GPIO_PortSourceGPIOA, GPIO_PinSource1);
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    EXTI_InitStructure.EXTI_Line    = EXTI_Line1;
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    EXTI_InitStructure.EXTI_LineCmd = ENABLE;
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    EXTI_InitStructure.EXTI_Mode    = EXTI_Mode_Interrupt;  // EXTI 中断模式
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    EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Falling; // 按下时触发
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    EXTI_Init(&EXTI_InitStructure);
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    NVIC_InitStructure.NVIC_IRQChannel = EXTI1_IRQn;
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    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
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    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1; // 抢占优先级
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    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0; // 响应优先级
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    NVIC_Init(&NVIC_InitStructure);
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}
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// EXTI_Line1 的中断处理函数，可从 startup_stm32xxx.s 中查到
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void EXTI1_IRQHandler(){
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    // 避免错误进入中断
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    if(EXTI_GetITStatus(EXTI_Line1) != RESET){
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        // 处理中断, 不要在这儿写复杂的运算或是Delay
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        // 清除请求挂起寄存器对应位
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        EXTI_ClearITPendingBit(EXTI_Line1);
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    }
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}
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int main(void){
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  // 务必配置中断优先级分组
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  NVIC_SetPriorityGrouping(2);
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  EXTI_Config();
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  // ...
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}