Input capture timer - measure the correct frequency

[mfcprog]

Posted on April 17, 2012 at 15:01

Hi,

I want to capture a signal with 30Hz frequency by a timer input capture. The timer is already working but the measured frequency is not 30Hz. I always measure a frequency of 29.85Hz or 30.3Hz. Are there any mistakes according to may selected period or prescaler values? By the way I`m using the STM32F103XC processor.

void TIMER_InitInputCaptureTimer(TIM_TypeDef* TIMx, unsigned short tmrchannel, unsigned short period)

{   TIM_ICInitTypeDef  TIM_ICInitStructure;  TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;  unsigned short PrescalerValue = (unsigned short) (SYSTEM_TIMERCLOCK / TIMER_TAKT) - 1;

 TIM_TimeBaseStructure.TIM_Period       = period -1; //65535;

   TIM_TimeBaseStructure.TIM_Prescaler     = (TIMER_TAKT - 1); //0;    TIM_TimeBaseStructure.TIM_ClockDivision    = 0;    TIM_TimeBaseStructure.TIM_CounterMode     = TIM_CounterMode_Up;    TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;     TIM_TimeBaseInit(TIMx, &TIM_TimeBaseStructure);

 TIM_PrescalerConfig(TIMx, PrescalerValue, TIM_PSCReloadMode_Immediate);

 TIM_ICInitStructure.TIM_Channel = tmrchannel; //TIM_Channel_3;

   TIM_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Rising;    TIM_ICInitStructure.TIM_ICSelection = TIM_ICSelection_DirectTI;    TIM_ICInitStructure.TIM_ICPrescaler = TIM_ICPSC_DIV1;      // Div:1, every edge    TIM_ICInitStructure.TIM_ICFilter = 0x3;    TIM_ICInit(TIMx, &TIM_ICInitStructure);

 /* Enable the CC3 Interrupt Request */

   TIM_ClearITPendingBit(TIM1, tmrchannel); //TIM_IT_CC3);  TIM_ITConfig(TIMx, tmrchannel, ENABLE);

}

void TIMER_Init(TIM_TypeDef* TIMx, unsigned char mode, unsigned short tmrchannel, unsigned char irqchannel,

 unsigned short period, unsigned short fps) {  NVIC_InitTypeDef NVIC_InitStructure;

 switch(mode)

 {  case TMR_MODE_UPD:   TIMER_InitUpdTimer(TIMx, tmrchannel, fps);   break;

 case TMR_MODE_INPUTCAPTURE:

  TIMER_InitInputCaptureTimer(TIMx, tmrchannel, period);   break;

 default:

  return;  }      NVIC_InitStructure.NVIC_IRQChannel = irqchannel; //TIM1_CC_IRQChannel;    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;    NVIC_Init(&NVIC_InitStructure); } And that`s my call of the timer function: volatile unsigned short IC3ReadValue1 = 0, IC3ReadValue2 = 0; volatile unsigned short CaptureNumber = 0; volatile unsigned int Capture = 0; volatile unsigned int TIM1Freq = 0;  int d2i(float d) {  float value;  value = d;  value /= 10;  value += 0.5;  return value; } TIMER_Init(TIM1, TMR_MODE_INPUTCAPTURE, TIM_Channel_3, TIM1_CC_IRQChannel, 64800, 0); TIM_Cmd(TIM1, ENABLE); My Interrupt ISR:

void TIM1_CC_IRQHandler (void)

{    TIM1->SR & TIM_IT_CC3)  {  /* capture timer */        //clear pending bit   TIM1->SR = (unsigned short)~TIM_FLAG_CC3;

  if(CaptureNumber == 0)

     {        /* Get the Input Capture value */        IC3ReadValue1 = TIM1->CCR3;        CaptureNumber = 1;      }   else if(CaptureNumber == 1)      {        /* Get the Input Capture value */        IC3ReadValue2 = TIM1->CCR3;

       /* Capture computation */

       if (IC3ReadValue2 > IC3ReadValue1)        {          Capture = (IC3ReadValue2 - IC3ReadValue1);        }        else        {          Capture = ((0xFFFF - IC3ReadValue1) + IC3ReadValue2);        }        /* Frequency computation */     TIM1Freq =  d2i ((float)(2 * TIMER_TAKT * 10 / Capture));

          CaptureNumber = 0;

   }

  /* flag: new rising edge interrupt INTR received */

  captureFlag++;  /* clear all flags */     TIM1->SR = ~0xFF;    } } I hope someone of you could give me some hints to measure the exact frequency of the input signal. best regards Hans

[Cesar cfg]

Posted on February 28, 2013 at 08:09

Hi Clive: 

After searching in the NET i found this example but also we have a problem the results are not Ok .the code:  TIM_DeInit(TIM3 ); /* TIM3 clock enable */ RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE); /* GPIOC clock enable */ RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOD, ENABLE); GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6 | GPIO_Pin_7 | GPIO_Pin_8 | GPIO_Pin_9; GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF; GPIO_InitStructure.GPIO_Speed = GPIO_Speed_2MHz; GPIO_InitStructure.GPIO_OType = GPIO_OType_PP; GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP; GPIO_Init(GPIOC, &GPIO_InitStructure);GPIO_PinAFConfig(GPIOC, GPIO_PinSource6, GPIO_AF_0 );GPIO_PinAFConfig(GPIOC, GPIO_PinSource7, GPIO_AF_0 ); GPIO_PinAFConfig(GPIOC, GPIO_PinSource8, GPIO_AF_0 ); GPIO_PinAFConfig(GPIOC, GPIO_PinSource9, GPIO_AF_0 ); /* Enable capture*/ 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 = 0; TIM_ICInit(TIM3, &TIM_ICInitStructure); TIM_ICInitStructure.TIM_Channel = TIM_Channel_2; TIM_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Falling; TIM_ICInitStructure.TIM_ICSelection = TIM_ICSelection_DirectTI; TIM_ICInitStructure.TIM_ICPrescaler = TIM_ICPSC_DIV1; TIM_ICInitStructure.TIM_ICFilter = 0; TIM_ICInit(TIM3, &TIM_ICInitStructure); TIM_ICInitStructure.TIM_Channel = TIM_Channel_3;  TIM_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Rising; TIM_ICInit(TIM3, &TIM_ICInitStructure); TIM_ICInitStructure.TIM_Channel = TIM_Channel_4;  TIM_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Falling; TIM_ICInit(TIM3, &TIM_ICInitStructure); /* Enable TIM3 */ TIM_Cmd(TIM3, ENABLE); /* Enable CC1-4 interrupt */ TIM_ITConfig(TIM3, TIM_IT_CC1 | TIM_IT_CC2 | TIM_IT_CC3 | TIM_IT_CC4, ENABLE); /* Clear CC1 Flag*/ TIM_ClearFlag(TIM3, TIM_FLAG_CC1 | TIM_FLAG_CC2 | TIM_FLAG_CC3 | TIM_FLAG_CC4 );       NVIC_InitStructure.NVIC_IRQChannel =  TIM3_IRQn;   NVIC_InitStructure.NVIC_IRQChannelPriority=2;   NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;   NVIC_Init(&NVIC_InitStructure);} void TIM3_IRQHandler() {  TIM_ICInitTypeDef                       TIM_ICInitStructure; if (TIM3 ->SR & TIM_IT_CC1 ) {  TIM3 ->SR &= (~TIM_IT_CC1 );  if (pulseState == 0) {   TIM_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Falling;   // Any time we get a rising edge on CH1, we reset the counter. All channels are   // phase aligned, so they all use this as a reference.   TIM_SetCounter(TIM3,0);  }   else   {   TIM_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Rising;   // Pull the value on the falling edge.   ccr[0] = TIM_GetCapture1(TIM3 );  }  pulseState = !pulseState;  // Reverse polarity.  TIM_ICInit(TIM3, &TIM_ICInitStructure); } if (TIM3 ->SR & TIM_IT_CC2 ) {  TIM3 ->SR &= (~TIM_IT_CC2 );  ccr[1] = TIM_GetCapture2(TIM3 ); } if (TIM3 ->SR & TIM_IT_CC3 ) {  TIM3 ->SR &= (~TIM_IT_CC3 );  ccr[2] = TIM_GetCapture3(TIM3 ); } if (TIM3 ->SR & TIM_IT_CC4 )  {  TIM3 ->SR &= (~TIM_IT_CC4 );   ccr[3] = TIM_GetCapture4(TIM3 ); }}