[STM32F10x] 利用定时器测量频率

硬件：STM32F103C8T6

　　平台：ARM-MDk V5.11

　　原理

　　利用STM32F10x的定时器的捕获(Capture)单元测量输入信号的频率。

　　基本原理是通过两次捕获达到的计数器的差值，来计算输入信号的频率。假如第一次捕获时计数器的值为Val1，第二次捕获计数器的值为Val2，

　　定时器的时钟频率为f_timer，那么输入信号的频率f_input为

　　　　　　　　　　　　　　　　　　　　f_input = _ftimer / (Val2 - Val1)         　　　　　　(Val2 > Val1)

　　或

　　　　　　　　　　　　　　　　　　　　f_input = _ftimer / (MaxVal - Val1 + Val2)        　 (Val2 ≤ Val1)

　　 其中MaxVal为定时器的最大计数值

　　

　　代码

　　以TIM2 CH4为例，定时器配置代码如下：

void CaptureConfig(void)
{
    TIM_ICInitTypeDef  TIM_ICInitStructure;
    
    TIM_ICInitStructure.TIM_Channel     = TIM_Channel_4;
    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(TIM2, &TIM_ICInitStructure);
    
    /* TIM enable counter */
    TIM_Cmd(TIM2, ENABLE);

    /* Enable the CC4 Interrupt Request */
    TIM_ITConfig(TIM2, TIM_IT_CC4, ENABLE);
}

　　配置NVIC，使能TIM2的捕获中断：

void BSP_IntConfig(void)
{
    NVIC_InitTypeDef NVIC_InitStructure;

    /* Enable the TIM2 global Interrupt */
    NVIC_InitStructure.NVIC_IRQChannel                        = TIM2_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority      = 0;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority             = 1;
    NVIC_InitStructure.NVIC_IRQChannelCmd                     = ENABLE;
    NVIC_Init(&NVIC_InitStructure);
}

　　在TIM2中断处理函数中计算出输入信号的频率：

void TIM2_IRQHandler(void)
{ 
    static U16   Capture, IC4ReadValue1, IC4ReadValue2;
    static U8    CaptureNumber = 0;
    
    if(TIM_GetITStatus(TIM2, TIM_IT_CC4) == SET) 
    {
        /* Clear TIM2 Capture compare interrupt pending bit */
        TIM_ClearITPendingBit(TIM2, TIM_IT_CC4);
        if(CaptureNumber == 0)
        {
            /* Get the Input Capture value */
            IC4ReadValue1 = TIM_GetCapture4(TIM2);
            CaptureNumber = 1;
        }
        else if(CaptureNumber == 1)
        {
            /* Get the Input Capture value */
            IC4ReadValue2 = TIM_GetCapture4(TIM2); 

            /* Capture computation */
            if (IC4ReadValue2 > IC4ReadValue1)
            {
                Capture = (IC4ReadValue2 - IC4ReadValue1); 
            }
            else
            {
                Capture = ((0xFFFF - IC4ReadValue1) + IC4ReadValue2); 
            }
            /* Frequency computation */ 
            Freq = (U32) SystemCoreClock / Capture;
            CaptureNumber = 0;
        }
    }
}

注意：Freq是个全局变量。