Timer 8 of STM32F4 Discovery don't work !

[naceur2311]

Posted on March 11, 2013 at 10:54

Hi,

I have problems with Timer 8 this time. I want to measure the frequency of an input signal. I have to use PB1 that's connected to TIM8_CH3

N

. The code seem correct but it doesn't give any frequency. The code is the following :The main function :int main(void){    /* TIM8 Configuration */  TIM_Config();  TIM_ICInitStructure.TIM_Channel     = TIM_Channel_3;   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(TIM8, &TIM_ICInitStructure);  TIM_Cmd(TIM8, ENABLE);  TIM_ITConfig(TIM8, TIM_IT_CC3, ENABLE);  while (1);}void TIM_Config(void){  GPIO_InitTypeDef GPIO_InitStructure;  NVIC_InitTypeDef NVIC_InitStructure;  RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM8, ENABLE);  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOB, ENABLE);  GPIO_InitStructure.GPIO_Pin   = GPIO_Pin_1;  GPIO_InitStructure.GPIO_Mode  = GPIO_Mode_AF;  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;  GPIO_InitStructure.GPIO_PuPd  = GPIO_PuPd_NOPULL;  GPIO_Init(GPIOB, &GPIO_InitStructure);  GPIO_PinAFConfig(GPIOB, GPIO_PinSource1, GPIO_AF_TIM8);  NVIC_InitStructure.NVIC_IRQChannel                   = TIM8_CC_IRQn;  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;  NVIC_InitStructure.NVIC_IRQChannelSubPriority        = 1;  NVIC_InitStructure.NVIC_IRQChannelCmd                = ENABLE;  NVIC_Init(&NVIC_InitStructure);}

The code of the interrupt routine is :

 void TIM8_CC_IRQHandler(void){  if(TIM_GetITStatus(TIM8, TIM_IT_CC3) == SET)  {    TIM_ClearITPendingBit(TIM8, TIM_IT_CC3);    if(CaptureNumber == 0)    {       IC3ReadValue1 = TIM_GetCapture3(TIM8);      CaptureNumber = 1;    }    else if(CaptureNumber == 1)    {      IC3ReadValue2 = TIM_GetCapture3(TIM8);      if (IC3ReadValue2 > IC3ReadValue1)      {        Capture = (IC3ReadValue2 - IC3ReadValue1);      }      else if (IC3ReadValue2 < IC3ReadValue1)      {        Capture = ((0xFFFF - IC3ReadValue1) + IC3ReadValue2);      }      else      {        Capture = 0;      }            TIM8Freq = (uint32_t) SystemCoreClock / Capture;      CaptureNumber = 0;    }  }}Any help to resolve this problem.Thanks.

[ppatel]

Posted on July 10, 2015 at 21:38I am not interrupting at 4MHz. how can i use external count mod?? I need to read CNT register??

[Tesla DeLorean]

Posted on July 10, 2015 at 21:59

...when i set 4 MHz frequency, it is showing 8MHz...

I am not interrupting at 4MHz.Really, and HAL_TIM_IC_CaptureCallback() is called by unicorns?You're reading consecutive values of a CCRx register, and measuring the delta ticks between input clock edges.If you were counting pulses, in External Clock mode, you'd sample TIMx->CNT with some periodicity, brief enough that the 16-bit count doesn't overflow. You could latch the value of count into some other TIMx->CCRx register, or via DMA.

[Tesla DeLorean]

Posted on July 10, 2015 at 22:01

As I've repeatedly pointed out in this thread, and others, this math is broken

 time = ((0xffff - counter)+time);