帮我用keil5写基于stm32f103zet6单片机的hc-sr04模块的超声波测距的代码

好的，下面是基于stm32f103zet6单片机的hc-sr04模块超声波测距的代码，使用Keil5编译：

#include "stm32f10x.h"
#include <stdio.h>

#define TRIG GPIO_Pin_5
#define ECHO GPIO_Pin_6

void delay_us(u32);
void delay_ms(u16);

int main(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;
    TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStruct;
    TIM_OCInitTypeDef TIM_OCInitStruct;
    NVIC_InitTypeDef NVIC_InitStructure;

    float distance = 0;
    char str[16];

    // 初始化GPIOB和TIM3
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB | RCC_APB2Periph_AFIO, ENABLE);
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);

    // 初始化GPIOB Pin5为输出模式和Pin6为输入模式
    GPIO_InitStructure.GPIO_Pin = TRIG;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(GPIOB, &GPIO_InitStructure);

    GPIO_InitStructure.GPIO_Pin = ECHO;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPU;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(GPIOB, &GPIO_InitStructure);

    // 初始化TIM3为1MHz计数频率，计数器自动重载，预分频系数为71，计数模式为向上计数
    TIM_TimeBaseInitStruct.TIM_Period = 0xFFFF;
    TIM_TimeBaseInitStruct.TIM_Prescaler = 71;
    TIM_TimeBaseInitStruct.TIM_ClockDivision = 0;
    TIM_TimeBaseInitStruct.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM3, &TIM_TimeBaseInitStruct);

    // 配置TIM3的PWM模式为模式2，输出比较模式为PWM1
    TIM_OCInitStruct.TIM_OCMode = TIM_OCMode_PWM2;
    TIM_OCInitStruct.TIM_OutputState = TIM_OutputState_Enable;
    TIM_OCInitStruct.TIM_Pulse = 0;
    TIM_OCInitStruct.TIM_OCPolarity = TIM_OCPolarity_High;
    TIM_OC1Init(TIM3, &TIM_OCInitStruct);

    // 配置TIM3中断
    NVIC_InitStructure.NVIC_IRQChannel = TIM3_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStructure);

    // 启动TIM3
    TIM_Cmd(TIM3, ENABLE);

    while(1)
    {
        // 发送10us的高电平脉冲
        GPIO_SetBits(GPIOB, TRIG);
        delay_us(10);
        GPIO_ResetBits(GPIOB, TRIG);

        // 等待ECHO引脚变高电平
        while(GPIO_ReadInputDataBit(GPIOB, ECHO) == RESET);

        // 启动计数器
        TIM_SetCounter(TIM3, 0);
        TIM_ITConfig(TIM3, TIM_IT_CC1, ENABLE);

        // 等待ECHO引脚变低电平
        while(GPIO_ReadInputDataBit(GPIOB, ECHO) == SET);

        // 关闭计数器
        TIM_ITConfig(TIM3, TIM_IT_CC1, DISABLE);
        distance = (float)TIM_GetCapture1(TIM3) / 58.0;

        sprintf(str, "Distance: %.2f cm\n", distance);
        printf(str);

        delay_ms(1000);
    }
}

void TIM3_IRQHandler(void)
{
    if(TIM_GetITStatus(TIM3, TIM_IT_CC1) != RESET)
    {
        TIM_ClearITPendingBit(TIM3, TIM_IT_CC1);
    }
}

void delay_us(u32 us)
{
    SysTick_Config(SystemCoreClock / 1000000);
    while(us--)
    {
        while(!(SysTick->CTRL & SysTick_CTRL_COUNTFLAG_Msk));
    }
    SysTick->CTRL &= ~SysTick_CTRL_ENABLE_Msk;
}

void delay_ms(u16 ms)
{
    SysTick_Config(SystemCoreClock / 1000);
    while(ms--)
    {
        while(!(SysTick->CTRL & SysTick_CTRL_COUNTFLAG_Msk));
    }
    SysTick->CTRL &= ~SysTick_CTRL_ENABLE_Msk;
}

这段代码会通过超声波测距模块hc-sr04测量距离，并将距离通过串口输出到PC端。同时，还使用了定时器TIM3来计时。