stm32 超声波代码

以下是 STM32 的超声波测距代码，供参考：

#include "stm32f10x.h"

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

void init_gpio(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;

    /* Enable GPIOA clock */
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);

    /* Configure PA0 as input floating */
    GPIO_InitStructure.GPIO_Pin = ECHO_PIN;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
    GPIO_Init(ECHO_PORT, &GPIO_InitStructure);

    /* Configure PA1 as push-pull 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);
}

void delay_us(uint32_t us)
{
    /* Configure SysTick */
    SysTick->LOAD = (us * SystemCoreClock / 1000000UL) - 1;
    SysTick->VAL = 0;
    SysTick->CTRL = SysTick_CTRL_CLKSOURCE_Msk | SysTick_CTRL_ENABLE_Msk;

    /* Wait until the SysTick timer reaches 0 */
    while (!(SysTick->CTRL & SysTick_CTRL_COUNTFLAG_Msk));

    /* Disable SysTick */
    SysTick->CTRL = 0;
}

float get_distance(void)
{
    uint32_t pulse_width;
    float distance;

    /* Send a 10us pulse to the TRIG pin */
    GPIO_SetBits(TRIG_PORT, TRIG_PIN);
    delay_us(10);
    GPIO_ResetBits(TRIG_PORT, TRIG_PIN);

    /* Wait for the ECHO pin to go high */
    while (!GPIO_ReadInputDataBit(ECHO_PORT, ECHO_PIN));

    /* Start the timer */
    TIM_Cmd(TIM2, ENABLE);

    /* Wait for the ECHO pin to go low */
    while (GPIO_ReadInputDataBit(ECHO_PORT, ECHO_PIN));

    /* Stop the timer */
    TIM_Cmd(TIM2, DISABLE);

    /* Calculate the pulse width in microseconds */
    pulse_width = TIM_GetCounter(TIM2);

    /* Calculate the distance in centimeters */
    distance = pulse_width / 58.0;

    return distance;
}

int main(void)
{
    float distance;

    /* Initialize GPIO */
    init_gpio();

    /* Initialize TIM2 */
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);
    TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
    TIM_TimeBaseStructure.TIM_Period = 0xFFFFFFFF;
    TIM_TimeBaseStructure.TIM_Prescaler = SystemCoreClock / 1000000UL - 1;
    TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);

    while (1)
    {
        /* Measure the distance */
        distance = get_distance();

        /* Do something with the distance */
        // ...
    }
}

这个代码使用的是 STM32F103C8T6 开发板，使用 TIM2 计时器来测量超声波回波的脉冲宽度，然后根据公式 `distance = pulse_width / 58.0` 计算距离。具体实现方式可参考代码注释。