GD32F350引脚有异常干扰信号输出

`GD32F350使用timer1，参照例程，通道1、2、3产生PWM信号正常，当不使用通道2、3时，PB10引脚有不固定的波形输出，怀疑是干扰信号。
void timer_config(void)
{
     /* -----------------------------------------------------------------------
     TIMER1 configuration: generate 3 PWM signals with 3 different duty cycles:
     TIMER1CLK is 1MHz

     TIMER1 channel1 duty cycle = (4000/ 16000)* 100  = 25%
     TIMER1 channel2 duty cycle = (8000/ 16000)* 100  = 50%
     TIMER1 channel3 duty cycle = (12000/ 16000)* 100 = 75%
     ----------------------------------------------------------------------- */
     timer_oc_parameter_struct timer_ocintpara;
     timer_parameter_struct timer_initpara;

     rcu_periph_clock_enable(RCU_TIMER1);

     timer_deinit(TIMER1);

     /* TIMER1 configuration */
#ifdef GD32F330
     timer_initpara.prescaler         = 83;
#endif /* GD32F330 */
#ifdef GD32F350
     timer_initpara.prescaler         = 107;
#endif /* GD32F350 */
     timer_initpara.alignedmode       = TIMER_COUNTER_EDGE;
     timer_initpara.counterdirection  = TIMER_COUNTER_UP;
     timer_initpara.period            = 15999;
     timer_initpara.clockdivision     = TIMER_CKDIV_DIV1;
     timer_initpara.repetitioncounter = 0;
     timer_init(TIMER1,&timer_initpara);

     /* CH1,CH2 and CH3 configuration in PWM mode0 */
     timer_ocintpara.ocpolarity  = TIMER_OC_POLARITY_HIGH;
     timer_ocintpara.outputstate = TIMER_CCX_ENABLE;

     timer_channel_output_config(TIMER1,TIMER_CH_1,&timer_ocintpara);

     timer_channel_output_pulse_value_config(TIMER1,TIMER_CH_1,3999);
     timer_channel_output_mode_config(TIMER1,TIMER_CH_1,TIMER_OC_MODE_PWM0);
     timer_channel_output_shadow_config(TIMER1,TIMER_CH_1,TIMER_OC_SHADOW_DISABLE);

     /* auto-reload preload enable */
     timer_auto_reload_shadow_enable(TIMER1);
     /* auto-reload preload enable */
     timer_enable(TIMER1);
}

void gpio_config(void)
{
     /*Configure PB3 PB10 PB11(TIMER1 CH1 CH2 CH3) as alternate function*/
     gpio_mode_set(GPIOB, GPIO_MODE_AF, GPIO_PUPD_NONE, GPIO_PIN_3);
     gpio_output_options_set(GPIOB, GPIO_OTYPE_PP, GPIO_OSPEED_50MHZ,GPIO_PIN_3);

    gpio_af_set(GPIOB, GPIO_AF_2, GPIO_PIN_3);

}
`