??? GPIO_InitTypeDef GPIO_InitStructure={0};
??? NVIC_InitTypeDef NVIC_InitStructure = {0};
??? TIM_OCInitTypeDef TIM_OCInitStructure={0};
??? TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructure={0};
??? RCC_APB2PeriphClockCmd( RCC_APB2Periph_GPIOB, ENABLE );
??? RCC_APB2PeriphClockCmd( RCC_APB2Periph_TIM8, ENABLE );
??? RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO, ENABLE);//使能AFIO复用功能模块时钟
??? GPIO_PinRemapConfig(GPIO_Remap_TIM8 , ENABLE);
??? GPIO_InitStructure.GPIO_Pin = X_PUL_GPIO;
??? GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
??? GPIO_InitStructure.GPIO_Speed = GPIO_Speed_2MHz;
??? GPIO_Init( X_PUL_PORT, &GPIO_InitStructure );
??? TIM_TimeBaseInitStructure.TIM_Period = arr;
??? TIM_TimeBaseInitStructure.TIM_Prescaler = psc;
??? TIM_TimeBaseInitStructure.TIM_ClockDivision = TIM_CKD_DIV1;
??? TIM_TimeBaseInitStructure.TIM_CounterMode = TIM_CounterMode_Up;
??? TIM_TimeBaseInit( X_TIM, &TIM_TimeBaseInitStructure);
??? TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
??? TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
??? TIM_OCInitStructure.TIM_Pulse = ccp;
??? TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
??? TIM_OC3Init( X_TIM, &TIM_OCInitStructure );
??? TIM_CtrlPWMOutputs(X_TIM, ENABLE );
??? TIM_OC3PreloadConfig( X_TIM, TIM_OCPreload_Enable );
??? TIM_ARRPreloadConfig( X_TIM, ENABLE );
??? TIM_Cmd( X_TIM, ENABLE );
??? TIM_ITConfig(X_TIM, TIM_IT_Update, ENABLE);
??? NVIC_InitStructure.NVIC_IRQChannel = TIM8_UP_IRQn;
??? NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
??? NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
??? NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
??? NVIC_Init(&NVIC_InitStructure);
以上是代码，PB8（TIM8_CH3）无法输出PWM?能帮忙看看是说明问题吗？
