stm32f205的计数问题，为何计数值比理论值减半

只看该作者 · 2014-11-13 08:43

香主你好，最近做了个stm32f205re的pwm输入捕获，系统时间为120mhz，捕获200hz占空比为50%的连续脉冲，脉宽为2.5ms，用32位定时器timer5进行计数，我设置最高速率的计数，2.5ms的时间内计数为156250左右，算下来一个计数值为16ns，理论计数应该8ns的。下面是我的定时器的初始化函数 TIM5_PWMINPUT_INIT(0xffffffff,0);
函数内容为void TIM5_PWMINPUT_INIT(u32 arr,u32 psc)
{

TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
NVIC_InitTypeDef NVIC_InitStructure;
TIM_ICInitTypeDef  TIM5_ICInitStructure;
GPIO_InitTypeDef GPIO_InitStructure;

RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM5, ENABLE);    //Open TIM5 clock
  RCC_APB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);  //open gpioB clock

//Connect TIM3 Pin to AF2
GPIO_PinAFConfig(GPIOA,GPIO_PinSource0,GPIO_AF_TIM5);  //TIM3_Ch2

// Config TIM3 Pin
/* TIM3 channel 2 pin (PA.07) configuration */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF; //
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);

TIM_TimeBaseStructure.TIM_Period = arr; //设置在下一个更新事件装入活动的自动重装载寄存器周期的值
TIM_TimeBaseStructure.TIM_Prescaler =psc; //设置用来作为TIMx时钟频率除数的预分频值
TIM_TimeBaseStructure.TIM_ClockDivision = 0; //设置时钟分割:TDTS = Tck_tim
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;  //TIM向上计数模式
TIM_TimeBaseInit(TIM5, &TIM_TimeBaseStructure); //根据TIM_TimeBaseInitStruct中指定的参数初始化TIMx的时间基数单位

/*配置中断优先级*/
NVIC_InitStructure.NVIC_IRQChannel = TIM5_IRQn;
  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
  NVIC_Init(&NVIC_InitStructure);

TIM5_ICInitStructure.TIM_Channel = TIM_Channel_1;
  TIM5_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Falling; //TIM_ICPolarity_Rising
  TIM5_ICInitStructure.TIM_ICSelection = TIM_ICSelection_DirectTI;
  TIM5_ICInitStructure.TIM_ICPrescaler = TIM_ICPSC_DIV1;
TIM5_ICInitStructure.TIM_ICFilter = 0x0;

TIM_PWMIConfig(TIM5, &TIM5_ICInitStructure);    //PWM输入配置
  TIM_SelectInputTrigger(TIM5, TIM_TS_TI1FP1);    //选择有效输入端 TIM_TS_TI2FP2
  TIM_SelectSlaveMode(TIM5, TIM_SlaveMode_Reset);  //配置为主从复位模式
  TIM_SelectMasterSlaveMode(TIM5, TIM_MasterSlaveMode_Enable);
  TIM_ITConfig(TIM5, TIM_IT_CC1, ENABLE);       //中断配置 TIM_IT_CC2 |TIM_IT_Update
TIM_ClearITPendingBit(TIM5, TIM_IT_CC1|TIM_IT_Update); //清除中断标志位 TIM_IT_CC2
TIM_Cmd(TIM5, ENABLE);
}

中断函数为

u32 jueyuan_xiangwei_buf[JY_XW_SIZE];
u16 jy_xw_counter=0;

void TIM5_IRQHandler(void)
{

   if(CollectFlag ==0 )
{
if (TIM_GetITStatus(TIM5, TIM_IT_CC1) != RESET)//捕获1发生捕获事件 TIM_IT_CC2
{
duty = TIM_GetCapture1(TIM5); //采集占空比
period = TIM_GetCapture2(TIM5);    //采集周期
jueyuan_xiangwei_buf[jy_xw_counter++] = period;
   if(jy_xw_counter >= JY_XW_SIZE)
{
      CollectFlag = 1;
jy_xw_counter =0;
}
}
   }
TIM_ClearITPendingBit(TIM5, TIM_IT_CC1|TIM_IT_Update); //清除中断标志位 TIM_IT_CC2

}

我是在仿真器里面查看数值的，请香主帮忙看看我的设置是否有问题，为啥实际值与计算值差一半呢？谢谢