源码如下，ETR脚（PA15)输入脉冲

void TIMER2_Counter_Init(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;
    TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
  
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE); 

    GPIO_PinAFConfig(GPIOA, GPIO_PinSource15, GPIO_AF_TIM2);

    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_15;
    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(GPIOA, &GPIO_InitStructure);

    RCC_APB2PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);
    
    TIM_DeInit(TIM2);

    TIM_TimeBaseStructure.TIM_Prescaler = 0x00;
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseStructure.TIM_Period = 0xFFFF;    
    TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseInit( TIM2, &TIM_TimeBaseStructure);

//    TIM_TIxExternalClockConfig(TIM2, TIM_TIxExternalCLK1Source_TI2, TIM_ICPolarity_Rising, 0);
//    TIM_ETRClockMode1Config(TIM2, TIM_ExtTRGPSC_OFF, TIM_ExtTRGPolarity_NonInverted, 0);
    TIM_ETRClockMode2Config(TIM2, TIM_ExtTRGPSC_OFF, TIM_ExtTRGPolarity_NonInverted, 0);

    TIM_SetCounter(TIM2, 0);
    
    TIM_Cmd(TIM2, ENABLE);
}