stm32 TIM3中断一直进不去，求大虾指点

yunlong14781 提问时间：2012-4-8 15:28 /

void TIM3_Configuration()
{
   TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
   RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);
   TIM_DeInit(TIM3);
   TIM_TimeBaseStructure.TIM_Period=2000;    //ARR的值
   TIM_TimeBaseStructure.TIM_Prescaler=36000;
   TIM_TimeBaseStructure.TIM_ClockDivision=0; //采样分频
   TIM_TimeBaseStructure.TIM_CounterMode=TIM_CounterMode_Up; //向上计数模式
   TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);
   TIM_ClearFlag(TIM3, TIM_FLAG_Update);
   TIM_ARRPreloadConfig(TIM3, DISABLE);//禁止ARR预装载缓冲器
   TIM_ITConfig(TIM3,TIM_IT_Update,ENABLE);
   TIM_Cmd(TIM3, ENABLE); //开启时钟
}
void NVIC_Configuration(void)
{

NVIC_InitTypeDef NVIC_InitStructure;

#ifdef VECT_TAB_RAM
  /* Set the Vector Table base location at 0x20000000 [设置中断向量表的起始位置0x20000000]*/
  NVIC_SetVectorTable(NVIC_VectTab_RAM, 0x0);
#else /* VECT_TAB_FLASH */
  /* Set the Vector Table base location at 0x08000000[设置中断向量表的起始位置0x0x08000000] */
  NVIC_SetVectorTable(NVIC_VectTab_FLASH, 0x0);
#endif
  NVIC_PriorityGroupConfig(NVIC_PriorityGroup_1);
  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);
}
void TIM3_IRQHandler(void)
{
  if(TIM_GetFlagStatus(TIM3,TIM_IT_Update)!=RESET)
  {
   //TIM_ClearITPendingBit(TIM3,TIM_FLAG_Update);
   GPIO_ResetBits(GPIOB,GPIO_Pin_3);
   count++;
   if(count>100)count=0;
  }
}