用ST的标准库配置PA8,PA9,PA10输出TIM1的PWM，一直没输出，代码如下：

RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA, ENABLE);
    GPIO_InitStructure.GPIO_Pin   = GPIO_Pin_8 | GPIO_Pin_9| GPIO_Pin_10;
    GPIO_InitStructure.GPIO_Mode  = GPIO_Mode_AF;
    GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
    //GPIO_InitStructure.GPIO_PuPd  = GPIO_PuPd_UP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    GPIO_PinAFConfig(GPIOA, GPIO_PinSource8, GPIO_AF_2); // TIM1_CH1
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource9, GPIO_AF_2); // TIM1_CH2
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource10, GPIO_AF_2); // TIM1_CH3

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM1, ENABLE); //使能定时器1
    TIM_TimeBaseStructure.TIM_Period = 1000 - 1;        // ARR
    TIM_TimeBaseStructure.TIM_Prescaler = 48 -1;      // PSC
    TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;
    TIM_TimeBaseInit(TIM1, &TIM_TimeBaseStructure);



        TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
        TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable; // 通道输出使能
        TIM_OCInitStructure.TIM_OutputNState = TIM_OutputNState_Disable; // 互补通道关闭
        TIM_OCInitStructure.TIM_Pulse = 500; // 初始占空比CCR1=0
        TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High; // 有效电平高
        TIM_OC1Init(TIM1, &TIM_OCInitStructure);
        TIM_OC1PreloadConfig(TIM1, TIM_OCPreload_Enable); // 使能CCR预装载
        TIM_OC2Init(TIM1, &TIM_OCInitStructure);
        TIM_OC2PreloadConfig(TIM1, TIM_OCPreload_Enable); // 使能CCR预装载
        TIM_OC3Init(TIM1, &TIM_OCInitStructure);
        TIM_OC3PreloadConfig(TIM1, TIM_OCPreload_Enable); // 使能CCR预装载


    TIM_BDTRInitStructure.TIM_OSSRState = TIM_OSSRState_Disable;
    TIM_BDTRInitStructure.TIM_OSSIState = TIM_OSSIState_Disable;
    TIM_BDTRInitStructure.TIM_LOCKLevel = TIM_LOCKLevel_OFF;
    TIM_BDTRInitStructure.TIM_DeadTime = 0;         
    TIM_BDTRInitStructure.TIM_Break = TIM_Break_Disable;
    TIM_BDTRInitStructure.TIM_BreakPolarity = TIM_BreakPolarity_Low;
    TIM_BDTRInitStructure.TIM_AutomaticOutput = TIM_AutomaticOutput_Disable;
    TIM_BDTRConfig(TIM1, &TIM_BDTRInitStructure);


    TIM_CtrlPWMOutputs(TIM1, ENABLE);
    TIM_ARRPreloadConfig(TIM1, ENABLE);

    TIM_Cmd(TIM1, ENABLE);



这样配置是不是哪里有问题？