lm3s9b90通过timer方式配置PWM 为何 不出现波形？？？？？？？？ TI员工辛苦呢 求教 ？？？？

    SysCtlClockSet(SYSCTL_SYSDIV_1 | SYSCTL_USE_OSC | SYSCTL_OSC_MAIN | SYSCTL_XTAL_16MHZ);
    
    SysCtlPeripheralEnable(SYSCTL_PERIPH_TIMER1);

    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOE);

    GPIOPinConfigure(GPIO_PE4_CCP2);

    GPIOPinTypeTimer(GPIO_PORTE_BASE, GPIO_PIN_4);

 

    TimerConfigure(TIMER1_BASE, TIMER_CFG_16_BIT_PAIR | TIMER_CFG_A_PWM);

    TimerControlLevel(TIMER1_BASE, TIMER_A, true);

    TimerLoadSet(TIMER1_BASE, TIMER_A, 20000);

    TimerMatchSet(TIMER1_BASE, TIMER_A,  10000);

    TimerEnable(TIMER1_BASE, TIMER_A);

求教 求教