写一个stm32F103C8T6超声波测距代码

以下是一个简单的超声波测距代码，基于STM32F103C8T6的定时器和外部中断实现：

#include "stm32f10x.h"

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

uint16_t distance = 0;

void TIM2_IRQHandler(void) {
    if (TIM_GetITStatus(TIM2, TIM_IT_Update) != RESET) {
        // 超时未检测到回波，停止计时
        TIM_Cmd(TIM2, DISABLE);
        TIM_SetCounter(TIM2, 0);
        TIM_ClearITPendingBit(TIM2, TIM_IT_Update);
    }
}

void EXTI1_IRQHandler(void) {
    if (EXTI_GetITStatus(EXTI_Line1) != RESET) {
        if (GPIO_ReadInputDataBit(ECHO_PORT, ECHO_PIN)) {
            // 上升沿，开始计时
            TIM_SetCounter(TIM2, 0);
            TIM_Cmd(TIM2, ENABLE);
        } else {
            // 下降沿，计算距离
            uint16_t cnt = TIM_GetCounter(TIM2);
            distance = cnt / 58; // 距离单位为厘米
            TIM_Cmd(TIM2, DISABLE);
            TIM_SetCounter(TIM2, 0);
        }
        EXTI_ClearITPendingBit(EXTI_Line1);
    }
}

void init_gpio(void) {
    GPIO_InitTypeDef GPIO_InitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);

    // 配置TRIG引脚为输出模式
    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);

    // 配置ECHO引脚为输入模式
    GPIO_InitStructure.GPIO_Pin = ECHO_PIN;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPU;
    GPIO_Init(ECHO_PORT, &GPIO_InitStructure);
}

void init_tim(void) {
    TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;

    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);

    TIM_TimeBaseStructure.TIM_Period = 0xFFFF;
    TIM_TimeBaseStructure.TIM_Prescaler = SystemCoreClock / 1000000 - 1;
    TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);

    TIM_ITConfig(TIM2, TIM_IT_Update, ENABLE);
    NVIC_EnableIRQ(TIM2_IRQn);
}

void init_exti(void) {
    EXTI_InitTypeDef EXTI_InitStructure;
    NVIC_InitTypeDef NVIC_InitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO, ENABLE);
    GPIO_EXTILineConfig(GPIO_PortSourceGPIOA, GPIO_PinSource1);

    EXTI_InitStructure.EXTI_Line = EXTI_Line1;
    EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt;
    EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Rising_Falling;
    EXTI_InitStructure.EXTI_LineCmd = ENABLE;
    EXTI_Init(&EXTI_InitStructure);

    NVIC_InitStructure.NVIC_IRQChannel = EXTI1_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0x02;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0x02;
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStructure);
}

void delay_us(uint16_t us) {
    uint16_t i, j;
    for (i = 0; i < us; i++) {
        for (j = 0; j < 10; j++);
    }
}

int main(void) {
    init_gpio();
    init_tim();
    init_exti();

    while (1) {
        // 发送10us的触发脉冲
        GPIO_ResetBits(TRIG_PORT, TRIG_PIN);
        delay_us(2);
        GPIO_SetBits(TRIG_PORT, TRIG_PIN);
        delay_us(10);
        GPIO_ResetBits(TRIG_PORT, TRIG_PIN);

        // 延时等待回波
        delay_us(500);

        // 读取距离值
        printf("distance: %d cm\r\n", distance);
    }
}

以上代码仅供参考，具体实现方式可能会因为硬件和环境等因素而有所变化。