用TIM3接霍尔传感器，霍尔信号跳变的原因？

     用tiM3 接 霍尔传感器；3根霍尔信号异或，霍尔信号跳变，将触发TIM_IT_Trigger 中断；但是实际过程中，不管我怎么转动无刷电机，霍尔信号一直在变化，但是 void TIM3_IRQHandler(void) 中断里，就是没有  TIF 中断标记 即 if(TIM3->SR 0x0040)无法调用； （TIM3中断其他类型的中断是有的，譬如TIM3->SR 0x0010）怎么办啊？，
void TIM3_Configuration(void)
{
   TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
   TIM_ICInitTypeDef TIM_ICInitStructure;         
   TIM_OCInitTypeDef  TIM_OCInitStructure;         

   TIM_DeInit(TIM3);

   TIM_TimeBaseStructure.TIM_Prescaler = 71;                        
   TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
   TIM_TimeBaseStructure.TIM_Period =65535;
   TIM_TimeBaseStructure.TIM_ClockDivision = 0;
   TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;

   TIM_TimeBaseInit(TIM3, TIM_TimeBaseStructure);     

    TIM_ICInitStructure.TIM_Channel = TIM_Channel_1;            
    TIM_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Rising;
    TIM_ICInitStructure.TIM_ICSelection = TIM_ICSelection_TRC ;
    TIM_ICInitStructure.TIM_ICPrescaler = TIM_ICPSC_DIV1;      
    TIM_ICInitStructure.TIM_ICFilter = 10;                       

    TIM_ICInit(TIM3,  TIM_ICInitStructure);                     

   TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2;                     
   TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;            
   TIM_OCInitStructure.TIM_Pulse =1023;
   TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;      

   TIM_OC2Init(TIM3, TIM_OCInitStructure);

   TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_Timing;                     
   TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Disable;            
   TIM_OCInitStructure.TIM_Pulse =65535;
   TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;      

   TIM_OC4Init(TIM3, TIM_OCInitStructure);

   TIM_SelectHallSensor(TIM3,ENABLE);                          

   TIM_SelectInputTrigger(TIM3, TIM_TS_TI1F_ED);                  

   TIM_SelectSlaveMode(TIM3, TIM_SlaveMode_Reset);            

   TIM_SelectMasterSlaveMode(TIM3, TIM_MasterSlaveMode_Enable);        

   TIM_SelectOutputTrigger(TIM3, TIM_TRGOSource_OC2Ref );      

   TIM_ITConfig(TIM3, TIM_IT_Trigger|TIM_IT_CC4, ENABLE);  

   //TIM_Cmd(TIM3,ENABLE);
}