stm32f100x discovery board input capture problem

[adhiyanrs]

Posted on December 13, 2014 at 16:34

Hello every one ,

I am using stm32vl discovery board for PWM input capture.I am using TIM3 channel 2 and counter clock frequency is 24MHz  with this i can measure the frequency and duty cycle of input PWM only till 367Hz.But i am facing problems in configuring prescalar value  to measure even lesser input frequency . please help me out in  setting prescalar value  . code which i am using is as belowmain codeint main(void){            /* System Clocks Configuration */  RCC_Configuration();  /* NVIC configuration */  NVIC_Configuration();  /* Configure the GPIO ports */  GPIO_Configuration();    TIM_ICInitStructure.TIM_Channel = TIM_Channel_2;  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_PWMIConfig(TIM3, &TIM_ICInitStructure);  /* Select the TIM3 Input Trigger: TI2FP2 */  TIM_SelectInputTrigger(TIM3, TIM_TS_TI2FP2);  /* Select the slave Mode: Reset Mode */  TIM_SelectSlaveMode(TIM3, TIM_SlaveMode_Reset);  /* Enable the Master/Slave Mode */  TIM_SelectMasterSlaveMode(TIM3, TIM_MasterSlaveMode_Enable);  /* TIM enable counter */  TIM_Cmd(TIM3, ENABLE);  /* Enable the CC2 Interrupt Request */  TIM_ITConfig(TIM3, TIM_IT_CC2, ENABLE);  while (1);}void RCC_Configuration(void){  /* TIM3 clock enable */  RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);  /* GPIOA clock enable */  RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);}void GPIO_Configuration(void){  GPIO_InitTypeDef GPIO_InitStructure;  /* TIM3 channel 2 pin (PA.07) configuration */  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_7;  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;  GPIO_Init(GPIOA, &GPIO_InitStructure);}void NVIC_Configuration(void){  NVIC_InitTypeDef NVIC_InitStructure;  /* Enable the TIM3 global Interrupt */  NVIC_InitStructure.NVIC_IRQChannel = TIM3_IRQn;  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;  NVIC_Init(&NVIC_InitStructure);}Timer interrupt handler code void TIM3_IRQHandler(void){  /* Clear TIM3 Capture compare interrupt pending bit */  TIM_ClearITPendingBit(TIM3, TIM_IT_CC2);  /* Get the Input Capture value */  IC2Value = TIM_GetCapture2(TIM3);  if (IC2Value != 0)  {    /* Duty cycle computation */    DutyCycle = (TIM_GetCapture1(TIM3) * 100) / IC2Value;    /* Frequency computation */    Frequency = SystemCoreClock / IC2Value;  }  else  {    DutyCycle = 0;    Frequency = 0;  }} 

[Tesla DeLorean]

Posted on December 13, 2014 at 21:29

You'd need to configure the time base to a suitable frequency, and then adjust your frequency computation to use the time base frequency, and not the system one.

TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
uint32_t PrescalerValue;
/* Compute the prescaler value */
PrescalerValue = (SystemCoreClock / 1000000); // 1MHz time base
/* Time base configuration */
TIM_TimeBaseStructure.TIM_Period = 65535; // Maximal
TIM_TimeBaseStructure.TIM_Prescaler = (uint16_t)PrescalerValue - 1;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseStructure.TIM_ClockDivision = 0; // Input sychronizer
TIM_TimeBaseStructure.TIM_RepetitionCounter = 0; // Unused
TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);
...
/* Frequency computation */
Frequency = (SystemCoreClock / IC2Value) / PrescalerValue;