m451 PWM1_CH4捕获不了怎么处理？

m451 PWM1_CH4 捕获不了。
进入不了这个中断，void PWM1P1_IRQHandler(void)
应该要如何处理？


        /* set PWM1 channel 4 capture configuration */
        PWM_ConfigCaptureChannel(PWM1, 4, 69, 0);

        /* Enable capture falling edge interrupt for PWM1 channel 4 */
        PWM_EnableCaptureInt(PWM1, 4, PWM_CAPTURE_INT_FALLING_LATCH);

        /* Enable PWM1 NVIC interrupt */
        NVIC_EnableIRQ(PWM1P1_IRQn);

        /* Enable Timer for PWM1 channel 2 */
        PWM_Start(PWM1, PWM_CH_4_MASK);

        /* Enable Capture Function for PWM1 channel 4 */
        PWM_EnableCapture(PWM1, PWM_CH_4_MASK);

        /* Enable falling capture reload */
        PWM1->CAPCTL |= PWM_CAPCTL_FCRLDEN4_Msk;


void PWM_EnableCapture(PWM_T *pwm, uint32_t u32ChannelMask);