STM32单定时器四通道捕获功能实现
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输入捕获作为定时器的一个功能，在工业测速上有很大的应用。STM32的一些定时器具有四个外部通道，可利用一个定时器采集外部四路脉冲频率，节约硬件资源和软件代码
如需要测量一个或多个外部方波脉冲频率，频率低于单片机运行频率，可如下操作：（以TIM4为例）
初始化：(省略GPIO配置，将TIM4的四个通道引脚配置为上拉或浮空输入，省略定时器RCC配置，省略中断NVIC配置)
void TIM_Configuration(void)
{
TIM_ICInitTypeDef TIM_ICInitStructure;
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure; // TIM4 时基
TIM_DeInit(TIM4);
TIM_TimeBaseStructure.TIM_Period =0xffff;//自动重装值
TIM_TimeBaseStructure.TIM_Prescaler =719;//预分频值, 使TIMx_CLK=1MHz
TIM_TimeBaseStructure.TIM_ClockDivision =TIM_CKD_DIV1;//输入时钟不分频
TIM_TimeBaseStructure.TIM_CounterMode =TIM_CounterMode_Up;//向上计数
TIM_TimeBaseInit(TIM4,&TIM_TimeBaseStructure);//TIM4_TimeBase
// TIM_ICInitStructure.TIM_ICMode =TIM_ICMode_ICAP; //输入捕捉方式
TIM_ICInitStructure.TIM_Channel = TIM_Channel_1;//|TIM_Channel_2; //输入通道
TIM_ICInitStructure.TIM_ICPolarity =TIM_ICPolarity_Rising; //捕捉上升沿
TIM_ICInitStructure.TIM_ICSelection =TIM_ICSelection_DirectTI; //捕捉中断
TIM_ICInitStructure.TIM_ICPrescaler =TIM_ICPSC_DIV1; //捕捉不分频
TIM_ICInitStructure.TIM_ICFilter =0x0; //捕捉输入不滤波
TIM_ICInit(TIM4, &TIM_ICInitStructure);
TIM_ICInitStructure.TIM_Channel = TIM_Channel_2 ;//|TIM_Channel_2; //输入通道
TIM_ICInitStructure.TIM_ICPolarity =TIM_ICPolarity_Rising; //捕捉上升沿
TIM_ICInitStructure.TIM_ICSelection =TIM_ICSelection_DirectTI; //捕捉中断
TIM_ICInitStructure.TIM_ICPrescaler =TIM_ICPSC_DIV1; //捕捉不分频
TIM_ICInitStructure.TIM_ICFilter =0x0; //捕捉输入不滤波
TIM_ICInit(TIM4, &TIM_ICInitStructure);
TIM_ICInitStructure.TIM_Channel = TIM_Channel_3 ;//|TIM_Channel_2; //输入通道
TIM_ICInitStructure.TIM_ICPolarity =TIM_ICPolarity_Rising; //捕捉上升沿
TIM_ICInitStructure.TIM_ICSelection =TIM_ICSelection_DirectTI; //捕捉中断
TIM_ICInitStructure.TIM_ICPrescaler =TIM_ICPSC_DIV1; //捕捉不分频
TIM_ICInitStructure.TIM_ICFilter =0x0; //捕捉输入不滤波
TIM_ICInit(TIM4, &TIM_ICInitStructure);
TIM_ICInitStructure.TIM_Channel = TIM_Channel_4 ;//|TIM_Channel_2; //输入通道
TIM_ICInitStructure.TIM_ICPolarity =TIM_ICPolarity_Rising; //捕捉上升沿
TIM_ICInitStructure.TIM_ICSelection =TIM_ICSelection_DirectTI; //捕捉中断
TIM_ICInitStructure.TIM_ICPrescaler =TIM_ICPSC_DIV1; //捕捉不分频
TIM_ICInitStructure.TIM_ICFilter =0x0; //捕捉输入不滤波
TIM_ICInit(TIM4, &TIM_ICInitStructure);
TIM_Cmd(TIM4, ENABLE);
TIM_ITConfig(TIM4, TIM_IT_CC1, ENABLE);
TIM_ITConfig(TIM4, TIM_IT_CC2, ENABLE);
TIM_ITConfig(TIM4, TIM_IT_CC3, ENABLE);
TIM_ITConfig(TIM4, TIM_IT_CC4, ENABLE);
}
其中：
TIM_TimeBaseStructure.TIM_Period = 0xffff;为自动重装值，与普通单片机一样
TIM_TimeBaseStructure.TIM_Prescaler = 719; 预分频值, 使TIMx_CLK=100KHz ，系统时钟运行于72M时720分频，定时器运行于100KHZ，即10us每分度
TIM_ICInitStructure.TIM_ICMode = TIM_ICMode_ICAP; 此句选择定时器为输入捕获模式，但在我的库函数下未定义，所以注释掉，未影响程序执行
TIM_ICInitStructure.TIM_Channel = TIM_Channel_1;配置通道1
TIM_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Rising;上升沿捕获
TIM_ICInitStructure.TIM_ICSelection = TIM_ICSelection_DirectTI;捕获中断
TIM_ICInitStructure.TIM_ICFilter = 0x0;不滤波
TIM_ICInit(TIM4, &TIM_ICInitStructure);将配置应用
以上每个通道都需要将整个配置再写一遍，使用与'|'是无效的。
TIM_Cmd(TIM4, ENABLE);使能定时器4
TIM_ITConfig(TIM4, TIM_IT_CC1, ENABLE);
TIM_ITConfig(TIM4, TIM_IT_CC2, ENABLE);
TIM_ITConfig(TIM4, TIM_IT_CC3, ENABLE);
TIM_ITConfig(TIM4, TIM_IT_CC4, ENABLE);打开四个通道的捕获中断
以上将TIM配置完成，下面是中断内代码：
void
TIM4_IRQHandler(void)
{
//频率缓冲区计数
static u16 this_time_CH1 = 0;
static u16 last_time_CH1 = 0;
static u8 capture_number_CH1 = 0;
vu16 tmp16_CH1;
static u16 this_time_CH2 = 0;
static u16 last_time_CH2 = 0;
static u8 capture_number_CH2 = 0;
vu16 tmp16_CH2;
static u16 this_time_CH3 = 0;
static u16 last_time_CH3 = 0;
static u8 capture_number_CH3 = 0;
vu16 tmp16_CH3;
static u16 this_time_CH4 = 0;
static u16 last_time_CH4 = 0;
static u8 capture_number_CH4 = 0;
vu16 tmp16_CH4;
if(TIM_GetITStatus(TIM4, TIM_IT_CC1) == SET)
{
TIM_ClearITPendingBit(TIM4, TIM_IT_CC1);
if(capture_number_CH1 == 0)
{
capture_number_CH1 = 1;
last_time_CH1 = TIM_GetCapture1(TIM4);
}
else if(capture_number_CH1 == 1)
{
capture_number_CH1 = 0;
this_time_CH1 = TIM_GetCapture1(TIM4);
if(this_time_CH1 > last_time_CH1)
{
tmp16_CH1 = (this_time_CH1 - last_time_CH1);
}
else
{
tmp16_CH1 = ((0xFFFF - last_time_CH1) + this_time_CH1);
}
//TIM2 counter clock = 1MHz
//
FreqBuf[cnt] = (1000000L * 100) / tmp16; //*100为扩大显示量程
Freq_Value[0]=tmp16_CH1;
}
}
if(TIM_GetITStatus(TIM4, TIM_IT_CC2) == SET)
{
TIM_ClearITPendingBit(TIM4, TIM_IT_CC2);
if(capture_number_CH2 == 0)
{
capture_number_CH2 = 1;
last_time_CH2 = TIM_GetCapture2(TIM4);
}
else if(capture_number_CH2 == 1)
{
capture_number_CH2 = 0;
this_time_CH2 = TIM_GetCapture2(TIM4);
if(this_time_CH2 > last_time_CH2)
{
tmp16_CH2 = (this_time_CH2 - last_time_CH2);
}
else
{
tmp16_CH2 = ((0xFFFF - last_time_CH2) + this_time_CH2);
}
//TIM2 counter clock = 1MHz
//
FreqBuf[cnt] = (1000000L * 100) / tmp16; //*100为扩大显示量程
Freq_Value[1]=tmp16_CH2;
}
}
if(TIM_GetITStatus(TIM4, TIM_IT_CC3) == SET)
{
TIM_ClearITPendingBit(TIM4, TIM_IT_CC3);
if(capture_number_CH3 == 0)
{
capture_number_CH3 = 1;
last_time_CH3 = TIM_GetCapture3(TIM4);
}
else if(capture_number_CH3 == 1)
{
capture_number_CH3 = 0;
this_time_CH3 = TIM_GetCapture3(TIM4);
if(this_time_CH3 > last_time_CH3)
{
tmp16_CH3 = (this_time_CH3 - last_time_CH3);
}
else
{
tmp16_CH3 = ((0xFFFF - last_time_CH3) + this_time_CH3);
}
//TIM2 counter clock = 1MHz //
FreqBuf[cnt] = (1000000L * 100) / tmp16; //*100为扩大显示量程
Freq_Value[2]=tmp16_CH3;
}
}
if(TIM_GetITStatus(TIM4, TIM_IT_CC4) == SET)
{
TIM_ClearITPendingBit(TIM4, TIM_IT_CC4);
if(capture_number_CH4 == 0)
{
capture_number_CH4 = 1;
last_time_CH4 = TIM_GetCapture4(TIM4);
}
else if(capture_number_CH4 == 1)
{
capture_number_CH4 = 0;
this_time_CH4 = TIM_GetCapture4(TIM4);
if(this_time_CH4 > last_time_CH4)
{
tmp16_CH4 = (this_time_CH4 - last_time_CH4);
}
else
{
tmp16_CH4 = ((0xFFFF - last_time_CH4) + this_time_CH4);
}
//TIM2 counter clock = 1MHz //
FreqBuf[cnt] = (1000000L * 100) / tmp16; //*100为扩大显示量程
Freq_Value[3]=tmp16_CH4;
}
}//
GPIO_WriteBit(GPIOC, GPIO_Pin_13,(BitAction)((1-GPIO_ReadOutputDataBit(GPIOC, GPIO_Pin_13))));
}
中断内四部分代码完全一样，只分析其中一段输入捕获的原理是，
定时器正常计数运行，当外部脉冲到来时，将定时器计数值存起来，当下次脉冲到来时，求出这两次计数值差值，即为这两段脉冲的周期。
例如，
定时器计数到10，外部脉冲到来，使用last_time_CH1存储10，
下次脉冲到来，此时定时器计数值运行到110，使用this_time_CH1存储110，
之后做差，tmp16_CH1存储差值100，由于定时器运行于100KHZ，10us计数值增加一次，所以脉冲周期为100*10=1000us=1ms，即为1KHZ。
当然，定时器会溢出重装，此时需要将差值补偿运算，tmp16_CH1 = ((0xFFFF - last_time_CH1) + this_time_CH1);
可测量的范围取决于定时器运行的频率，如果外部频率慢到当定时器整个计数一周后也没有触发两次，会发生溢出，此时计数值已不准确。
所以定时器时钟配置取决于外部脉冲频率，应配置得当使得脉冲频率范围不致溢出。
由于每次外部脉冲都会触发中断，尤其是四通道时，所以使用中断方式会略微占用CPU资源，使用DMA可以解决这一问题。
得到脉冲周期后，即可通过运算获得外部频率，进而测速。
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