写一个STM32的HC-SR04测距函数

好的，以下是一个基于STM32的HC-SR04测距函数的示例代码：

#include "stm32f10x.h"

#define TRIG_PIN GPIO_Pin_0
#define ECHO_PIN GPIO_Pin_1
#define TRIG_PORT GPIOA
#define ECHO_PORT GPIOA

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

float hc_sr04_measure_distance(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;
    TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
    TIM_ICInitTypeDef TIM_ICInitStructure;
    NVIC_InitTypeDef NVIC_InitStructure;

    float distance;
    uint32_t pulse_width;
    uint32_t timeout;

    // Enable GPIOA and TIM2 clocks
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);

    // Configure TRIG pin as output
    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);

    // Configure ECHO pin as input
    GPIO_InitStructure.GPIO_Pin = ECHO_PIN;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPD;
    GPIO_Init(ECHO_PORT, &GPIO_InitStructure);

    // Configure TIM2 for input capture mode
    TIM_TimeBaseStructure.TIM_Period = 0xFFFF;
    TIM_TimeBaseStructure.TIM_Prescaler = 72 - 1;
    TIM_TimeBaseStructure.TIM_ClockDivision = 0;
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);

    TIM_ICInitStructure.TIM_Channel = TIM_Channel_2;
    TIM_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Rising;
    TIM_ICInitStructure.TIM_ICSelection = TIM_ICSelection_DirectTI;
    TIM_ICInitStructure.TIM_ICPrescaler = TIM_ICPSC_DIV1;
    TIM_ICInitStructure.TIM_ICFilter = 0;
    TIM_ICInit(TIM2, &TIM_ICInitStructure);

    // Enable TIM2 interrupt
    NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStructure);

    // Generate 10us pulse on TRIG pin
    GPIO_SetBits(TRIG_PORT, TRIG_PIN);
    delay_us(10);
    GPIO_ResetBits(TRIG_PORT, TRIG_PIN);

    // Wait for ECHO pin to go high
    timeout = 0;
    while(!GPIO_ReadInputDataBit(ECHO_PORT, ECHO_PIN))
    {
        if(timeout++ > 10000)
            return -1;
    }

    // Start TIM2
    TIM_Cmd(TIM2, ENABLE);

    // Wait for ECHO pin to go low
    timeout = 0;
    while(GPIO_ReadInputDataBit(ECHO_PORT, ECHO_PIN))
    {
        if(timeout++ > 10000)
            return -1;
    }

    // Stop TIM2
    TIM_Cmd(TIM2, DISABLE);

    // Calculate pulse width
    pulse_width = TIM_GetCapture2(TIM2);

    // Calculate distance in cm
    distance = pulse_width * 0.034 / 2;

    return distance;
}

void TIM2_IRQHandler(void)
{
    TIM_ClearITPendingBit(TIM2, TIM_IT_CC2);
}

这个函数使用STM32的定时器和输入捕获功能来测量HC-SR04超声波传感器返回的脉冲宽度，并计算出距离。