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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 enable counter */
- TIM_Cmd(TIM4, ENABLE);
- /* Enable the CC2 Interrupt Request */
- 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);
- }
复制代码 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))));
- }
复制代码 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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