Posted on July 27, 2016 at 09:37Hi. I'm having problem trying to use input capture mode to measure frequency. I create pwn signal from timer4 of microprocessor and try to mesure it's frequency via timer2 input capture. I also measure the frequncy via ossiloscope. The problem is frequencies I measure from ossiloscope an input capture don't match. I have deviation. For higher frequencies higher deviation. For example for 5000Hz I measure 5084, for 87kHz I measure 131kHz.
My code is below. Pelease help me.
#include <stm32f4xx.h>
uint32_t count;
float frequency;
int main()
{
GPIO_InitTypeDef GPIO_InitStructure;
TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructure;
TIM_ICInitTypeDef TIM_ICInitStructure;
NVIC_InitTypeDef NVIC_InitStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;
RCC_HSEConfig(RCC_HSE_ON);
while(!RCC_GetFlagStatus(RCC_FLAG_HSERDY));
RCC_SYSCLKConfig(RCC_SYSCLKSource_HSE);
RCC_PCLK2Config(RCC_HCLK_Div1);
RCC_PCLK1Config(RCC_HCLK_Div1);
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA,ENABLE);
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOB,ENABLE);
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD,ENABLE);
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2,ENABLE);
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM4,ENABLE);
//Kesme
NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQn;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
NVIC_Init(&NVIC_InitStructure);
//GPIOD pwm output
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_15;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
GPIO_Init(GPIOD,&GPIO_InitStructure);
GPIO_PinAFConfig(GPIOD,GPIO_PinSource15,GPIO_AF_TIM4);
//GPIOA bit 0 capture input
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
GPIO_Init(GPIOA,&GPIO_InitStructure);
GPIO_PinAFConfig(GPIOA,GPIO_PinSource0,GPIO_AF_TIM2);
//TIMER4 pwm adjustments
TIM_TimeBaseInitStructure.TIM_ClockDivision = TIM_CKD_DIV1;
TIM_TimeBaseInitStructure.TIM_Period = 800/9;
TIM_TimeBaseInitStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInitStructure.TIM_Prescaler = 0;
TIM_TimeBaseInit(TIM4,&TIM_TimeBaseInitStructure);
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStructure.TIM_Pulse = 40-1;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
TIM_OC4Init(TIM4,&TIM_OCInitStructure);
//TIM2 capture adjustments
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_DIV8;
TIM_ICInitStructure.TIM_ICFilter = 0;
TIM_ICInit(TIM2,&TIM_ICInitStructure);
TIM_ClearFlag(TIM2,TIM_FLAG_CC1);
TIM_ITConfig(TIM2,TIM_IT_CC1,ENABLE);
TIM_SetCounter(TIM2,0);
TIM_Cmd(TIM4,ENABLE);
TIM_Cmd(TIM2,ENABLE);
while(1)
{
}
}
void TIM2_IRQHandler()
{
count = TIM_GetCapture1(TIM2);
frequency = 64000000.0/count;
TIM_SetCounter(TIM2,0);
TIM_ClearFlag(TIM2,TIM_FLAG_CC1);
}
