在 void USB_Interrupts_Config(void) 里面为什么要加外部中断的配置
/* Configure the EXti line 18 connected internally to the USB IP */
EXTI_ClearITPendingBit(EXTI_Line18);
EXTI_InitStructure.EXTI_Line = EXTI_Line18; // USB resume from suspend mode
EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Rising;
EXTI_InitStructure.EXTI_LineCmd = ENABLE;
EXTI_Init(&EXTI_InitStructure);