下午学习了中断和外部中断，其中NVIC控制和EXTI控制，NVIC给每个中断赋予先占优先级和次占优先级，NVIC通过优先级分组来分配先占优先级和次占优先级的数量。EXTI负责管理映射到GPIO引脚上的外中断和片内几个集成外设的中断以及软件中断。
NVIC_InitStructure.NVIC_IRQChannel = EXTI0_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);
GPIO_EXTILineConfig(GPIO_PortSourceGPIOB, GPIO_PinSource0);
EXTI_InitStructure.EXTI_Line = EXTI_Line0;
EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt;
EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Falling;
EXTI_InitStructure.EXTI_LineCmd = ENABLE;
EXTI_Init(&EXTI_InitStructure);
EXTI0_IRQn的值，其实就是EXTI0中断向量在中断向量表中的位置。
