STM32F103 6路互补信号中有三路PWM信号输出有间断

我的STM32F103RCT6 tim8输出6路互补信号中有三路PWM信号输出有间断，请问可能是什么原因导致的，麻烦各位高人帮我看看．调了很久了，找不到原因．
以下贴出代码。

//初始化Tim8
void MotorLeft_Hw_PWM_Init(void)
{
    by_Direct = 0;
    by_Step = 0;
    w_PWM_Save = 0;

    GPIO_InitTypeDef        GPIO_InitStructure;
    NVIC_InitTypeDef        NVIC_InitStructure;
    TIM_OCInitTypeDef       TIM_OCInitStructure;
    TIM_BDTRInitTypeDef     TIM_BDTRInitStructure;
    TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;

    /* GPIOA Configuration: Channel 1, 2 and 3 as alternate function push-pull */
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8 | GPIO_Pin_9 | GPIO_Pin_10;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    /* GPIOB Configuration: Channel 1N, 2N and 3N as alternate function push-pull */
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_13 | GPIO_Pin_14 | GPIO_Pin_15;
    GPIO_Init(GPIOB, &GPIO_InitStructure);

    /* GPIOB Configuration: BKIN pin */
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_12;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
    GPIO_Init(GPIOB, &GPIO_InitStructure);  


    /* Time Base configuration */
    TIM_TimeBaseStructure.TIM_Prescaler = 0;
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseStructure.TIM_Period = 3499;
    TIM_TimeBaseStructure.TIM_ClockDivision = 0;
    TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;

    TIM_TimeBaseInit(TIM1, &TIM_TimeBaseStructure);

    /* Channel 1, 2,3 and 4 Configuration in PWM mode */
    TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
    TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
    TIM_OCInitStructure.TIM_OutputNState = TIM_OutputNState_Enable;
    TIM_OCInitStructure.TIM_Pulse = 0;
    TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;;
    TIM_OCInitStructure.TIM_OCNPolarity = TIM_OCNPolarity_High;
    TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Reset;
    TIM_OCInitStructure.TIM_OCNIdleState = TIM_OCNIdleState_Reset;

    TIM_OC1Init(TIM1, &TIM_OCInitStructure);
    TIM_OC2Init(TIM1, &TIM_OCInitStructure);
    TIM_OC3Init(TIM1, &TIM_OCInitStructure);

    /* Automatic Output enable, Break, dead time and lock configuration*/
    TIM_BDTRInitStructure.TIM_OSSRState = TIM_OSSRState_Enable;
    TIM_BDTRInitStructure.TIM_OSSIState = TIM_OSSIState_Enable;
    TIM_BDTRInitStructure.TIM_LOCKLevel = TIM_LOCKLevel_OFF;
    TIM_BDTRInitStructure.TIM_DeadTime = 0xFF;
    TIM_BDTRInitStructure.TIM_Break = TIM_Break_Enable;
    TIM_BDTRInitStructure.TIM_BreakPolarity = TIM_BreakPolarity_High;
    TIM_BDTRInitStructure.TIM_AutomaticOutput = TIM_AutomaticOutput_Enable;
    TIM_BDTRConfig(TIM1, &TIM_BDTRInitStructure);

    TIM_ClearITPendingBit(TIM1, TIM_IT_Break);
    TIM_ITConfig(TIM1, TIM_IT_Break, ENABLE);

    TIM_CCPreloadControl(TIM1, ENABLE);
    TIM_ITConfig(TIM1, TIM_IT_COM, ENABLE);
    TIM_Cmd(TIM1, ENABLE);
    TIM_CtrlPWMOutputs(TIM1, ENABLE);


    NVIC_InitStructure.NVIC_IRQChannel = TIM1_TRG_COM_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0x00;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStructure);
}


//输出PWM
void MotorLeft_Hw_Hall_Int(UCHAR by_State)
{
    switch(by_Step)
    {
    case 5:
    default:
        MotorLeft_Hw_PWM(0, 1749);
        /* Next by_Step: by_Step 1 (A+,C-)Configuration ---------------------------- */
        /*  Channel2 configuration */
        TIM_CCxCmd(TIM1, TIM_Channel_2, TIM_CCx_Disable);
        TIM_CCxNCmd(TIM1, TIM_Channel_2, TIM_CCxN_Disable);

        /*  Channel1 configuration */
        TIM_SelectOCxM(TIM1, TIM_Channel_1, TIM_OCMode_PWM1);
        TIM_CCxCmd(TIM1, TIM_Channel_1, TIM_CCx_Enable);
        TIM_CCxNCmd(TIM1, TIM_Channel_1, TIM_CCxN_Disable);

        /*  Channel3 configuration */
        TIM_SelectOCxM(TIM1, TIM_Channel_3, TIM_OCMode_PWM1);
        TIM_CCxCmd(TIM1, TIM_Channel_3, TIM_CCx_Disable);
        TIM_CCxNCmd(TIM1, TIM_Channel_3, TIM_CCxN_Enable);
        by_Step = 4;
        break;
    case 4:
        /* Next by_Step: by_Step 2 (A+,B-)Configuration ---------------------------- */
        /*  Channel3 configuration */
        TIM_CCxCmd(TIM1, TIM_Channel_3, TIM_CCx_Disable);
        TIM_CCxNCmd(TIM1, TIM_Channel_3, TIM_CCxN_Disable);

        /*  Channel1 configuration */
        TIM_SelectOCxM(TIM1, TIM_Channel_1, TIM_OCMode_PWM1);
        TIM_CCxCmd(TIM1, TIM_Channel_1, TIM_CCx_Enable);
        TIM_CCxNCmd(TIM1, TIM_Channel_1, TIM_CCxN_Disable);

        /*  Channel2 configuration */
        TIM_SelectOCxM(TIM1, TIM_Channel_2, TIM_OCMode_PWM1 );
        TIM_CCxCmd(TIM1, TIM_Channel_2, TIM_CCx_Disable);
        TIM_CCxNCmd(TIM1, TIM_Channel_2, TIM_CCxN_Enable);
        by_Step = 6;
        break;
    case 6:
        /* Next by_Step: by_Step 3 (C+,B-)Configuration ---------------------------- */
        /*  Channel1 configuration */
        TIM_CCxCmd(TIM1, TIM_Channel_1, TIM_CCx_Disable);
        TIM_CCxNCmd(TIM1, TIM_Channel_1, TIM_CCxN_Disable);

        /*  Channel3 configuration */
        TIM_SelectOCxM(TIM1, TIM_Channel_3, TIM_OCMode_PWM1);
        TIM_CCxCmd(TIM1, TIM_Channel_3, TIM_CCx_Enable);
        TIM_CCxNCmd(TIM1, TIM_Channel_3, TIM_CCxN_Disable);

        /*  Channel2 configuration */
        TIM_SelectOCxM(TIM1, TIM_Channel_2, TIM_OCMode_PWM1);
        TIM_CCxCmd(TIM1, TIM_Channel_2, TIM_CCx_Disable);
        TIM_CCxNCmd(TIM1, TIM_Channel_2, TIM_CCxN_Enable);
        by_Step = 2;
        break;
    case 2:
        /* Next by_Step: by_Step 4 (C+,A-)Configuration ---------------------------- */
        /*  Channel2 configuration */
        TIM_CCxCmd(TIM1, TIM_Channel_2, TIM_CCx_Disable);
        TIM_CCxNCmd(TIM1, TIM_Channel_2, TIM_CCxN_Disable);

        /*  Channel3 configuration */
        TIM_SelectOCxM(TIM1, TIM_Channel_3, TIM_OCMode_PWM1);
        TIM_CCxCmd(TIM1, TIM_Channel_3, TIM_CCx_Enable);
        TIM_CCxNCmd(TIM1, TIM_Channel_3, TIM_CCxN_Disable);

        /*  Channel1 configuration */
        TIM_SelectOCxM(TIM1, TIM_Channel_1, TIM_OCMode_PWM1);
        TIM_CCxCmd(TIM1, TIM_Channel_1, TIM_CCx_Disable);
        TIM_CCxNCmd(TIM1, TIM_Channel_1, TIM_CCxN_Enable);
        by_Step = 3;
        break;
    case 3:
        /* Next by_Step: by_Step 5 (B+,A-)Configuration ---------------------------- */
        /*  Channel3 configuration */
        TIM_CCxCmd(TIM1, TIM_Channel_3, TIM_CCx_Disable);
        TIM_CCxNCmd(TIM1, TIM_Channel_3, TIM_CCxN_Disable);

        /*  Channel2 configuration */
        TIM_SelectOCxM(TIM1, TIM_Channel_2, TIM_OCMode_PWM1);
        TIM_CCxCmd(TIM1, TIM_Channel_2, TIM_CCx_Enable);
        TIM_CCxNCmd(TIM1, TIM_Channel_2, TIM_CCxN_Disable);

        /*  Channel1 configuration */
        TIM_SelectOCxM(TIM1, TIM_Channel_1, TIM_OCMode_PWM1);
        TIM_CCxCmd(TIM1, TIM_Channel_1, TIM_CCx_Disable);
        TIM_CCxNCmd(TIM1, TIM_Channel_1, TIM_CCxN_Enable);
        by_Step = 1;
        break;
    case 1:
        /* Next by_Step: by_Step 6 (B+,C-)Configuration ---------------------------- */
        /*  Channel1 configuration */
        TIM_CCxCmd(TIM1, TIM_Channel_1, TIM_CCx_Disable);
        TIM_CCxNCmd(TIM1, TIM_Channel_1, TIM_CCxN_Disable);

        /*  Channel2 configuration */
        TIM_SelectOCxM(TIM1, TIM_Channel_2, TIM_OCMode_PWM1);
        TIM_CCxCmd(TIM1, TIM_Channel_2, TIM_CCx_Enable);
        TIM_CCxNCmd(TIM1, TIM_Channel_2, TIM_CCxN_Disable);

        /*  Channel3 configuration */
        TIM_SelectOCxM(TIM1, TIM_Channel_3, TIM_OCMode_PWM1);
        TIM_CCxCmd(TIM1, TIM_Channel_3, TIM_CCx_Disable);
        TIM_CCxNCmd(TIM1, TIM_Channel_3, TIM_CCxN_Enable);
        by_Step = 5;
        break;
    }
}