如何用STM32配置一个EXTIx中断线的I/O口-//NVIC_CONFIG（）;
//2.配置EXTIx线的中断优先级
NVIC_PriorityGroupConfig（NVIC_PriorityGroup_1）;
NVIC_InitStructure.NVIC_IRQChannel=EXTI3_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority=0;
NVIC_InitStructure.NVIC_IRQChannelSubPriority=0;
NVIC_InitStructure.NVIC_IRQChannelCmd=ENABLE;
NVIC_Init（&NVIC_InitStructure）;
