stm32测量方波频率

要测量方波的频率，可以使用STM32的定时器模块来实现。具体步骤如下：

1. 配置定时器的输入捕获模式，选择捕获上升沿或下降沿触发。

2. 配置定时器的时钟源和分频系数，使其能够计数到足够大的值。

3. 在输入捕获中断中，记录当前的计数器值，并清除计数器。

4. 根据捕获到的两个计数器值之间的差值，计算出方波的周期和频率。

下面是一段示例代码，演示如何使用STM32的定时器模块来测量方波的频率：

#include "stm32f4xx.h"

#define TIMER_PRESCALER     84     // 定时器分频系数
#define TIMER_MAX_VALUE     0xFFFF // 定时器最大计数值

uint32_t capture_value1 = 0;
uint32_t capture_value2 = 0;
uint32_t capture_diff = 0;

void TIM3_IRQHandler(void)
{
    if (TIM_GetITStatus(TIM3, TIM_IT_CC1) != RESET) {
        if (capture_value1 == 0) {
            capture_value1 = TIM_GetCapture1(TIM3);
        } else {
            capture_value2 = TIM_GetCapture1(TIM3);
            if (capture_value2 > capture_value1) {
                capture_diff = capture_value2 - capture_value1;
            } else {
                capture_diff = (TIMER_MAX_VALUE - capture_value1) + capture_value2 + 1;
            }
            capture_value1 = 0;
        }
        TIM_ClearITPendingBit(TIM3, TIM_IT_CC1);
    }
}

int main(void)
{
    // 初始化定时器
    TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
    TIM_TimeBaseStructure.TIM_Period = TIMER_MAX_VALUE;
    TIM_TimeBaseStructure.TIM_Prescaler = TIMER_PRESCALER - 1;
    TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);

    // 配置输入捕获通道
    TIM_ICInitTypeDef TIM_ICInitStructure;
    TIM_ICInitStructure.TIM_Channel = TIM_Channel_1;
    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 = 0x0;
    TIM_ICInit(TIM3, &TIM_ICInitStructure);

    // 使能输入捕获中断
    TIM_ITConfig(TIM3, TIM_IT_CC1, ENABLE);

    // 启动定时器
    TIM_Cmd(TIM3, ENABLE);

    // 配置中断服务程序
    NVIC_InitTypeDef NVIC_InitStructure;
    NVIC_InitStructure.NVIC_IRQChannel = TIM3_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStructure);

    while (1) {
        // 等待输入捕获中断发生
        if (capture_value1 != 0 && capture_value2 != 0) {
            // 计算方波的周期和频率
            uint32_t period = capture_diff * TIMER_PRESCALER;
            uint32_t frequency = SystemCoreClock / period;

            // 打印结果
            printf("Period: %lu us, Frequency: %lu Hz\r\n", period, frequency);

            // 清空捕获值
            capture_value1 = 0;
            capture_value2 = 0;
        }
    }
}

在上面的代码中，我们使用了TIM3定时器和捕获通道1来测量方波的频率。在输入捕获中断中，我们记录了两个捕获值，并计算出它们之间的差值，即方波的周期。最后，根据周期计算出方波的频率，并打印出结果。