STM32F4x输出pwm配置完后没有输出是为什么?怎么解决？

如题，我先配置GPIOPD12后配置tiM4_CH1,但是通过监测发现没有PWM 输出，不知道是不是哪儿出问题了，定时器CNT仿真看到是正常的，但是就是没有PWM输出到gpio上，看GPIO的寄存器ISTAT也没有变化，看看哪位大神指导一下，或者我是那个寄存器没配置对？：程序如下：
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD,ENABLE);
GPIO_StructInit( GPIO_InitStructure);GPIO_InitStructure.GPIO_Pin =GPIO_Pin_12;GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;GPIO_InitStructure.GPIO_OType = GPIO_OType_OD;GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP ;GPIO_Init(DI8_GPIO_PORT,  GPIO_InitStructure);GPIO_PinAFConfig(GPIOD, GPIO_PinSource12, GPIO_AF_TIM4);
TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure; //NVIC_InitTypeDef NVIC_InitStructure;  //NVICRCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM4, ENABLE);
TIM_TimeBaseStructure.TIM_Period = 21000-1;   //250usTIM_TimeBaseStructure.TIM_Prescaler =0;TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Down;TIM_TimeBaseInit(TIM4,  TIM_TimeBaseStructure);
TIM_SelectMasterSlaveMode(TIM4, TIM_MasterSlaveMode_Enable);TIM_SelectOutputTrigger(TIM4, TIM_TRGOSource_OC1Ref);TIM_ARRPreloadConfig(TIM4, ENABLE);
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;TIM_OCInitStructure.TIM_OutputNState = TIM_OutputNState_Enable;TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low; //TIM_OCNPolarity_High;TIM_OCInitStructure.TIM_OCNPolarity = TIM_OCNPolarity_Low;//TIM_OCNPolarity_High;TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Set;// TIM_OCIdleState_ResetTIM_OCInitStructure.TIM_OCNIdleState = TIM_OCNIdleState_Set;// TIM_OCNIdleState_ResetTIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2;TIM_OCInitStructure.TIM_Pulse = 10500+30;TIM_OC1Init(TIM4,  TIM_OCInitStructure);
TIM_OC1PreloadConfig(TIM4, TIM_OCPreload_Disable);