请问TIM1 ETR分频输出怎么配置

STM32F030上想用ETR做一个外部200kHz的时钟捕获以及分频，想做到每次外部时钟到来的时候触发ADC采样，通知对该时钟进行分频后输出，现在触发采样没问题了，但是分频输出没有搞定，大家帮忙看看怎么配置。
tiM_TimeBaseStructure.TIM_Prescaler = 0x00;
  TIM_TimeBaseStructure.TIM_Period = 1;//0xFFFF;
  TIM_TimeBaseStructure.TIM_ClockDivision = 0x0;
  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
  TIM_TimeBaseInit(TIM1, &TIM_TimeBaseStructure);  // Time base configuration

  TIM_ETRClockMode2Config(TIM1, TIM_ExtTRGPSC_OFF, TIM_ExtTRGPolarity_NonInverted, 0);   
  TIM_SelectOutputTrigger(TIM1,TIM_TRGOSource_Update);
  TIM_SetCounter(TIM1, 0);   
//以下为分频输出，使用TIM1 CH2
  TIM_OCStructInit(& TIM_OCInitStructure);
  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_Timing;
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
  TIM_OCInitStructure.TIM_Pulse = 20;
  TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
  TIM_OC2Init(TIM1, &TIM_OCInitStructure);

  TIM_OC2PreloadConfig(TIM1, TIM_OCPreload_Enable);

  TIM_ARRPreloadConfig(TIM1, ENABLE);

  TIM_CtrlPWMOutputs(TIM1, ENABLE);

  TIM_Cmd(TIM1, ENABLE);