写一个基于stm32使用hc-sr04超声波测距，同时模拟汽车倒车，当汽车离障碍物越近蜂鸣器响声越快的库函数

以下是基于STM32的HC-SR04超声波测距，同时模拟汽车倒车，当汽车离障碍物越近，蜂鸣器响声越快的库函数实现：

#include "stm32f10x.h"
#include "delay.h"

#define TRIG_PIN    GPIO_Pin_0
#define ECHO_PIN    GPIO_Pin_1
#define TRIG_PORT   GPIOA
#define ECHO_PORT   GPIOA
#define BUZZER_PIN  GPIO_Pin_2
#define BUZZER_PORT GPIOA

void HCSR04_Init(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);

    GPIO_InitStructure.GPIO_Pin = TRIG_PIN;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(TRIG_PORT, &GPIO_InitStructure);
    
    GPIO_InitStructure.GPIO_Pin = ECHO_PIN;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
    GPIO_Init(ECHO_PORT, &GPIO_InitStructure);
    
    GPIO_InitStructure.GPIO_Pin = BUZZER_PIN;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(BUZZER_PORT, &GPIO_InitStructure);
}

void HCSR04_Trigger(void)
{
    GPIO_SetBits(TRIG_PORT, TRIG_PIN);
    delay_us(10);
    GPIO_ResetBits(TRIG_PORT, TRIG_PIN);
}

float HCSR04_GetDistance(void)
{
    uint32_t time_out = 0;
    uint32_t time_in = 0;
    float distance = 0;

    HCSR04_Trigger();
    while(GPIO_ReadInputDataBit(ECHO_PORT, ECHO_PIN) == RESET) {
        time_out++;
        if(time_out > 100000) {
            return 0;
        }
        delay_us(10);
    }

    while(GPIO_ReadInputDataBit(ECHO_PORT, ECHO_PIN) == SET) {
        time_in++;
        if(time_in > 100000) {
            return 0;
        }
        delay_us(10);
    }

    distance = (float)(time_in * 0.017); // 计算距离，单位为厘米
    return distance;
}

void Buzzer_Alarm(float distance)
{
    uint32_t buzzer_delay = 0;

    if(distance <= 30) { // 如果离障碍物小于等于30厘米，蜂鸣器就开始响
        buzzer_delay = (uint32_t)(10000 / distance); // 计算蜂鸣器响声延迟时间，单位为毫秒，距离越近延迟越短，响声越快
        GPIO_SetBits(BUZZER_PORT, BUZZER_PIN);
        delay_ms(buzzer_delay);
        GPIO_ResetBits(BUZZER_PORT, BUZZER_PIN);
        delay_ms(buzzer_delay);
    }
}

int main(void)
{
    float distance = 0;

    HCSR04_Init();
    while(1) {
        distance = HCSR04_GetDistance();
        Buzzer_Alarm(distance);
        delay_ms(100);
    }
}

此代码中，我们使用了STM32的GPIO口控制HC-SR04超声波测距模块和蜂鸣器，通过调用库函数实现测距和控制蜂鸣器响声的功能。同时，在主函数中不断循环调用测距和蜂鸣器控制函数，以达到模拟汽车倒车的效果。