我是用STM32做一个酒精检测，超声波测距和密码锁，酒精检测采用MQ-3，直接AD转换；超声波测距是计高电平时间，利用公式计算出距离。

之前做好了酒精检测和超声波测距，但是后来莫名其妙超声波测距测不准了；现在加了密码锁之后，密码输入正确后，直接死了！

求大神帮助，下午检查成果。
超声波的程序
#include "ultrasonic.h"
#include "delay.h"
#include "stm32f10x.h"

int overcount1=0;

void NVIC_Config(void)
{
NVIC_InitTypeDef NVIC_InitStructer;
NVIC_InitStructer.NVIC_IRQChannelPreemptionPriority=0;
NVIC_InitStructer.NVIC_IRQChannelSubPriority=3;
NVIC_InitStructer.NVIC_IRQChannel=TIM4_IRQn;
NVIC_InitStructer.NVIC_IRQChannelCmd=ENABLE;
NVIC_Init(&NVIC_InitStructer);
}

void Ultrasonic_Init(void)
{
GPIO_InitTypeDef GPIO_InitStructer;
TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructer;
RCC_APB2PeriphClockCmd( RCC_APB2Periph_GPIOB, ENABLE);
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM4, ENABLE);
       

GPIO_InitStructer.GPIO_Speed=GPIO_Speed_50MHz;
GPIO_InitStructer.GPIO_Mode=GPIO_Mode_Out_PP;//íÆíìêä3ö
GPIO_InitStructer.GPIO_Pin=GPIO_Pin_7;
GPIO_Init(GPIOB, &GPIO_InitStructer);


GPIO_InitStructer.GPIO_Mode=GPIO_Mode_IN_FLOATING;
GPIO_InitStructer.GPIO_Pin=GPIO_Pin_6;
GPIO_Init(GPIOB, & GPIO_InitStructer);


TIM_DeInit(TIM4);
TIM_TimeBaseInitStructer.TIM_Period=999;
TIM_TimeBaseInitStructer.TIM_Prescaler=71;
TIM_TimeBaseInitStructer.TIM_ClockDivision=TIM_CKD_DIV1;
TIM_TimeBaseInitStructer.TIM_CounterMode=TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM4,&TIM_TimeBaseInitStructer);
TIM_ITConfig(TIM4,TIM_IT_Update,ENABLE);


NVIC_Config();
TIM_Cmd(TIM4,DISABLE);


}


float Distance_Gets(void)
{
float length=0,sum=0;
u16 tim;
int i=0;

while(i!=5)
{
//PBout(7)=1;  //à-¸ßTRIO
        GPIO_SetBits(GPIOB,GPIO_Pin_7);
  delay_us(20);  
//PBout(7)=0;
  GPIO_ResetBits(GPIOB,GPIO_Pin_7);

  while(GPIO_ReadInputDataBit(GPIOB,GPIO_Pin_6)==RESET);
  TIM_Cmd(TIM4,ENABLE);


i+=1;
while(GPIO_ReadInputDataBit(GPIOB,GPIO_Pin_6)==SET);

TIM_Cmd(TIM4,DISABLE);


tim=TIM_GetCounter(TIM4);

length=(tim+overcount1*1000)/10000*340/2;


sum=length+sum;
TIM4->CNT=0;  
overcount1=0;  
delay_ms(100);
}
length=sum/5;
return length;

}



void TIM4_IRQHandler(void)
{
if(TIM_GetITStatus(TIM4,TIM_IT_Update)!=RESET)

  {
TIM_ClearITPendingBit(TIM4,TIM_IT_Update);

overcount1++;

  }
}