基于MM32写出一个利用HC-SR04实现超声波测距功能，并显示在串口中

好的，下面是一个基于MM32的代码示例，实现了利用HC-SR04超声波模块测距，并将测得的距离通过串口输出显示。

#include "MM32F103.h"
#include "stdio.h"

#define TRIG_PIN    GPIO_Pin_0
#define ECHO_PIN    GPIO_Pin_1

void GPIO_Configuration(void);
void TIM_Configuration(void);
void USART_Configuration(void);
void delay_us(uint32_t us);
void delay_ms(uint32_t ms);
void USART_SendString(USART_TypeDef* USARTx, char* str);

int main(void)
{
    uint32_t distance = 0;
    char str[32] = {0};

    GPIO_Configuration();
    TIM_Configuration();
    USART_Configuration();

    while(1)
    {
        GPIO_ResetBits(GPIOA, TRIG_PIN);
        delay_us(2);
        GPIO_SetBits(GPIOA, TRIG_PIN);
        delay_us(10);
        GPIO_ResetBits(GPIOA, TRIG_PIN);

        while(GPIO_ReadInputDataBit(GPIOA, ECHO_PIN) == RESET);

        TIM_SetCounter(TIM2, 0);
        while(GPIO_ReadInputDataBit(GPIOA, ECHO_PIN) == SET);
        distance = TIM_GetCounter(TIM2) * 0.034 / 2;

        sprintf(str, "Distance: %d cm\n", distance);
        USART_SendString(USART1, str);

        delay_ms(500);
    }
}

void GPIO_Configuration(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(GPIOA, &GPIO_InitStructure);

    GPIO_InitStructure.GPIO_Pin = ECHO_PIN;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    GPIO_ResetBits(GPIOA, TRIG_PIN);
}

void TIM_Configuration(void)
{
    TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;

    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);

    TIM_TimeBaseStructure.TIM_Period = 0xFFFF;
    TIM_TimeBaseStructure.TIM_Prescaler = 72 - 1;
    TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);
}

void USART_Configuration(void)
{
    USART_InitTypeDef USART_InitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);

    USART_InitStructure.USART_BaudRate = 115200;
    USART_InitStructure.USART_WordLength = USART_WordLength_8b;
    USART_InitStructure.USART_StopBits = USART_StopBits_1;
    USART_InitStructure.USART_Parity = USART_Parity_No;
    USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
    USART_InitStructure.USART_Mode = USART_Mode_Tx;
    USART_Init(USART1, &USART_InitStructure);

    USART_Cmd(USART1, ENABLE);
}

void delay_us(uint32_t us)
{
    uint32_t i, j;
    for(i = 0; i < us; i++)
    {
        for(j = 0; j < 8; j++);
    }
}

void delay_ms(uint32_t ms)
{
    uint32_t i, j;
    for(i = 0; i < ms; i++)
    {
        for(j = 0; j < 8000; j++);
    }
}

void USART_SendString(USART_TypeDef* USARTx, char* str)
{
    while(*str)
    {
        USART_SendData(USARTx, (uint16_t)(*str++));
        while(USART_GetFlagStatus(USARTx, USART_FLAG_TXE) == RESET);
    }
}

需要注意的是，本代码示例中使用的是PA0和PA1引脚分别连接TRIG和ECHO引脚，需要根据实际硬件连接情况进行修改。同时，在使用测距功能时，需要将超声波模块与待测物体之间保持一定距离，避免测量出的距离受到干扰。