软件进入外部中断就停在startups.s中的B处
int main(void)
{
delay_init();
GPIOCLKInit();
UserLEDInit();
TIM2_Init();
MotorInit();
RedRayInit();
EXTI3_Config();
while(1)
{  
  CarGo();
  EXTI_GenerateSWInterrupt(EXTI_Line3);      
}
中断配置：

#include "interface.h"
#include "misc.h"
EXTI_InitTypeDef   EXTI_InitStructure;
GPIO_InitTypeDef   GPIO_InitStructure;
NVIC_InitTypeDef   NVIC_InitStructure;
void GPIOCLKInit(void)
{
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA , ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB , ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOC , ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOD , ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOE , ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOF , ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOG , ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO, ENABLE);
}

void EXTI3_Config()
{
/* Enable GPIOA clock */
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
  
  /* Configure PA.00 pin as input floating */
  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_3;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPU;
  GPIO_Init(GPIOA, &GPIO_InitStructure);
  /* Enable AFIO clock */
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO, ENABLE);
  /* Connect EXTI0 Line to PA.00 pin */
  GPIO_EXTILineConfig(GPIO_PortSourceGPIOA, GPIO_PinSource3);
  /* Configure EXTI0 line */
  EXTI_InitStructure.EXTI_Line = EXTI_Line3;
  EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt;
  EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Falling;  
  EXTI_InitStructure.EXTI_LineCmd = ENABLE;
  EXTI_Init(&EXTI_InitStructure);
  /* Enable and set EXTI0 Interrupt to the lowest priority */
  NVIC_InitStructure.NVIC_IRQChannel = EXTI3_IRQn;
  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0x0F;
  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0x0F;
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
  NVIC_Init(&NVIC_InitStructure);
}
中断服务程序：

void EXTI3_IRQHandle()
{
EXTI_ClearITPendingBit(EXTI_Line3);
EXTI_ClearFlag(EXTI_Line3);
}