Frequency Meansure

[felipe]

Posted on May 15, 2014 at 17:06

Hi,  I am using uvision4 with stm32f1xx to meansure frequency counting the time of the falling edge pulse. I need a high precision to meansure frequency from 0Hz to 240Hz. The first thing that I do was to set the prescaler to mensure 240Hz. That is ok, the problem is that I cant get when the timer count overflow to mensure frequency from 61 to 0. The program enter in theTIM_IT_Update all the time, what am I doing wrong?     void RCC_Configuration(void){

/* TIM2 clock enable */ RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE); TIM_TimeBaseStructure.TIM_Period = 65535; //20 mS TIM_TimeBaseStructure.TIM_Prescaler = Prescaler_Pickup - 1; //1 uS 1 MHz TIM_TimeBaseStructure.TIM_ClockDivision = 0; TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up; TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure); RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE); }   void TIM2_IRQHandler (void) { if(TIM_GetITStatus(TIM2, TIM_IT_CC1) == SET){ /* Clear TIM3 Capture compare interrupt pending bit */ TIM_ClearITPendingBit(TIM2, TIM_IT_CC1); if(CaptureNumber == 0){ /* Get the Input Capture value */ IC3ReadValue1 = TIM_GetCapture1(TIM2); CaptureNumber = 1; estourou_timer = 0; } else if(CaptureNumber == 1){ /* Get the Input Capture value */ IC3ReadValue2 = TIM_GetCapture1(TIM2); /* Capture computation */ if (IC3ReadValue2 > IC3ReadValue1){ Capture = (estourou_timer * 65535) + (IC3ReadValue2 - IC3ReadValue1); } else{ Capture = (estourou_timer * 65535) + ((0xFFFF - IC3ReadValue1) + IC3ReadValue2); } /* Frequency computation */ Pickup_1_FLOAT = (float) (72000000/Prescaler_Pickup) / Capture; if(Pickup_1_FLOAT < Menor_Med) Menor_Med = Pickup_1_FLOAT; CaptureNumber = 0; } }

if((TIM_GetITStatus(TIM2, TIM_IT_Update) == SET )){ //overflow

TIM_ClearITPendingBit(TIM2, TIM_FLAG_Update);

estourou_timer++;

}

}   void TIM2_Configuration(){

TIM_ICInitStructure.TIM_Channel = TIM_Channel_1; 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 = 0x0; TIM_ICInit(TIM2, &TIM_ICInitStructure); /* TIM enable counter */ TIM_Cmd(TIM2, ENABLE); /* Enable the CC1 Interrupt Request */ TIM_ITConfig(TIM2, TIM_IT_CC1 | TIM_IT_Update, ENABLE); TIM_ICInit(TIM2, &TIM_ICInitStructure); /* TIM enable counter */ TIM_Cmd(TIM2, ENABLE);    /* Enable the TIM3 global Interrupt */  NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQChannel;  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;  NVIC_Init(&NVIC_InitStructure);      }      

[Tesla DeLorean]

Posted on May 15, 2014 at 17:19

I swear I get the felling of DejaVu

The math here is totally broken:

/* Capture computation */
if (IC3ReadValue2 > IC3ReadValue1){
Capture = (estourou_timer * 65535) + (IC3ReadValue2 - IC3ReadValue1);
}
else{
Capture = (estourou_timer * 65535) + ((0xFFFF - IC3ReadValue1) + IC3ReadValue2);
}

I'm not going to look at this without a complete stand-alone example, where all the defines and variables are present in a fashion that can be compiled.

[felipe]

Posted on May 15, 2014 at 18:42Clive1,Sorry I forget to say that I just take the example STM32F10x_StdPeriph_Examples\TIM\InputCapture.The math is the same, I just put (estourou_timer * 65535) to sum the overflow time to compute low frequency.My problem is detecting the overflow as a sad.

[felipe]

Posted on May 19, 2014 at 16:41

Hi,

Someone can help me?I am stucked on this.Thanks

[chen]

Posted on May 19, 2014 at 18:22

''Someone can help me?

I am stucked on this.'' ''

I need a high precision to meansure frequency from 0Hz to 240Hz.

'' How is this high precision? 240Hz is hardly a high freq Do you need to know the fractional part of the frequency to a high degree of accuracy? Or just work out the frequency to the nearest Hz? In any case, you are going about it the hard way. 2 simple ways to do it : 1) Set up EXTI to count rising/falling edges, set up timer to capture count at known period and calculate the freq 2) set up one timer as a counter clocked by external freq, set up 2nd timer to capture count at known period and calculate the freq

[felipe]

Posted on May 19, 2014 at 19:17

Hi,

Thanks for the reply.I need to know the fractional part of the frequency.1) Set up EXTI to count rising/falling edges, set up timer to capture count at known period and calculate the freq.I am already doing it. My question is how can I use the

overflow flag

so I can ready low frequency (summing the overflow to my ''known period'').2)I know that I can use 2 timers and do a 32bit timer, but it will cost me hardward changes and programming time because I didnt find a example code.

[raptorhal2]

Posted on May 20, 2014 at 02:47

For each overflow, add 65536 to the timer count, obviously a 32 bit or longer integer.

You have to decide how low in frequency you wish to go. You can't wait forever for a pulse, and the timer overflows eventually overflow a 32 bit count. When you have waited as long as you can, declare the result to be zero frequency. Cheers, Hal

[felipe]

Posted on May 20, 2014 at 03:04

Hal,

Thank you for the reply.I understand what you sad, but it is another problem.The problem I am trying to resolve is that I cant get the overflow flag.So I didnt know when the overflow happen.Luis Felipe

[chen]

Posted on May 20, 2014 at 10:23

'' is how can I use the

overflow flag

'' What overflow flag? Your problem is that you have chosen to do this in a really hard way. Do not use the general timer (TIM2) - use the 32bit Timer (TIM1) Set this to a known high(ish) freq (calibrate it) Then just capture the 32 bit count. Use this to do the maths - it is EASIER. ''I didnt find a example code.'' For what you are doing - it is unlikely you will find an exact example. You are going to have to do some work and write your won code.

[felipe]

Posted on May 20, 2014 at 13:30

Hi,

Thanks for the help again. I have to do in this way because I am using 3 differents types of meters (project requirement) and I desagree with you when you say hard way. In my head it is so simple, I just have problem with knowing that the timer had an overflow! The overflow flag that I am talking is referenced in TIMx_SR in theRM0008 -Reference manual page Bit 0 UIF: Update interrupt flagThis bit is set by hardware on an update event. It is cleared by software.0: No update occurred.1: Update interrupt pending. This bit is set by hardware when the registers are updated:

–At overflow or underflow regarding the repetition counter value (update if repetition

counter = 0) and if the UDIS=0 in the TIMx_CR1 register.–When CNT is reinitialized by software using the UG bit in TIMx_EGR register, if URS=0and UDIS=0 in the TIMx_CR1 register.–When CNT is reinitialized by a trigger event (refer to Section 4.3: TIM1&TIM8 slavemode control register (TIMx_SMCR)), if URS=0 and UDIS=0 in the TIMx_CR1 register. I try to do in this way (after the Compare/Capture mode configurated as in the example of ST lib said in previous post):

if((TIM_GetITStatus(TIM2, TIM_IT_Update) == SET )){ //overflow
TIM_ClearITPendingBit(TIM2, TIM_FLAG_Update);
estourou_timer++;

}

and I have tried in this way too:

if ((TIM2->SR & 0x0001) != 0){
estourou_timer++;
TIM2->SR &= ~(1<<0); 
}

But the processor keep entering in the braces in frequencies that no overflow occur. How I know that overflow is not occurring? I use the Prescaler in 18, so: Clock frequency: 72Mhz/18 =4 Mhz. Time of overflow: (1/4Mhz)*65535 = 16,38ms

Frequency when overflow start:

1/16,38ms = 61Hz to 0Hz