[参考译文] TM4C123AE6PM：PWM 信号不会变为 0

尊敬的 Doug：

 我尝试了以下代码、并生成 0%占空比的 PWM、引脚始终为低电平。  

int
main(void)
{
    //
    // Set the clocking to run directly from the external crystal/oscillator.
    //
    MAP_SysCtlClockSet(SYSCTL_SYSDIV_1 | SYSCTL_USE_OSC | SYSCTL_OSC_MAIN |
                       SYSCTL_XTAL_16MHZ);

    //
    // Set the PWM clock to the system clock.
    //
    MAP_SysCtlPWMClockSet(SYSCTL_PWMDIV_1);

    //
    // Initialize the UART.
    //
    ConfigureUART();

    //
    // Display the setup on the console.
    //
    UARTprintf("PWM ->\n");
    UARTprintf("  Module: PWM0\n");
    UARTprintf("  Pin: PB6\n");
    UARTprintf("  Configured Duty Cycle: 25%%\n");
    UARTprintf("  Inverted Duty Cycle: 75%%\n");
    UARTprintf("  Features: PWM output inversion every 2 seconds.\n\n");
    UARTprintf("Generating PWM on PWM0 (PB6) -> State = ");

    //
    // The PWM peripheral must be enabled for use.
    //
    MAP_SysCtlPeripheralEnable(SYSCTL_PERIPH_PWM0);

    //
    // Enable the GPIO port that is used for the PWM output.
    //
    MAP_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOB);

    //
    // Configure the PWM function for this pin.
    //
    MAP_GPIOPinConfigure(GPIO_PB6_M0PWM0);
    MAP_GPIOPinTypePWM(GPIO_PORTB_BASE, GPIO_PIN_6);

    //
    // Configure PWM0 to count up/down without synchronization.
    //
    MAP_PWMGenConfigure(PWM0_BASE, PWM_GEN_0, PWM_GEN_MODE_UP_DOWN |
                        PWM_GEN_MODE_NO_SYNC);

    //
    // Set the PWM period to 250Hz.  To calculate the appropriate parameter
    // use the following equation: N = (1 / f) * SysClk.  Where N is the
    // function parameter, f is the desired frequency, and SysClk is the
    // system clock frequency.
    //
    MAP_PWMGenPeriodSet(PWM0_BASE, PWM_GEN_0, (SysCtlClockGet() / 250));

    //
    // Set PWM0 to a duty cycle of 0%.
    //
    MAP_PWMPulseWidthSet(PWM0_BASE, PWM_OUT_0,
                         0);

    //
    // Enable PWM Out Bit 0 (PB6) output signal.
    //
    MAP_PWMOutputState(PWM0_BASE, PWM_OUT_0_BIT, true);

    //
    // Enable the PWM generator block.
    //
    MAP_PWMGenEnable(PWM0_BASE, PWM_GEN_0);

    while (1);


}