What is correct initialization for QEI0 on Launchpad TM4C123G?

I have not been able to get the QEI0 on a LaunchPad TM4C123G working correctly.  I am using  CCS 5.1 and Tivaware 2.1.  The hardware seems to correctly produce the QEI pulses.  There is no index pulse.

I probably have the initialization sequence wrong, as this is my first use of the QEI, but just do not see the issue. I have other GPIO's and I2C working.  Posted below is the code snippet for the QEI0 initialization followed by the snippet in a forever loop in a task where I read the QEI0 value.

Previous initialization, not posted here, enables all GPIO peripherals. followed by some portc & portf initialization.

I have reviewed the Lock/unlock requirements for Port D7 (NMI), read the other posts in the forum, but am not at all confident that I correctly understand the Lock/Unlock procedure.

The values returned by the QEIPositionGet() alternate between 2 values.  These are the initialized value, which is 1234 in the code snippet, and 1233.

All help will be appreciated.

Randy

*********************************************************************************

void QEI0_Init (void)
{
    // qei init
    // *******************************************************************************
    //    Initialize QEI (Quadrature Encoder Interface).
    //    Use GPIO Port D bits PD6 & PD7 There is no Index.
    //    Port D pin 7 defaults to a NMI input at reset. That functionality
    //       must be "unlocked" before it can be made available to QEI0.
    // *******************************************************************************

    // PD7
    // PD7 requires unlocking before configuration
    HWREG                 (GPIO_PORTD_BASE + GPIO_O_LOCK) = GPIO_LOCK_KEY; // unlocks port
    HWREG                (GPIO_PORTD_BASE + GPIO_O_CR) = GPIO_LOCK_UNLOCKED;  // enables Commit register

    // Enable Port D module
    SysCtlPeripheralEnable (SYSCTL_PERIPH_GPIOD);
    SysCtlPeripheralEnable (SYSCTL_PERIPH_QEI0);

    // PD6
    GPIOPinConfigure     (GPIO_PD6_PHA0);
    GPIOPinTypeQEI         (GPIO_PORTD_BASE, GPIO_PIN_6);

    GPIOPinConfigure     (GPIO_PD7_PHB0);
    GPIOPinTypeQEI         (GPIO_PORTD_BASE, GPIO_PIN_7);

    // re-lock PD7
    HWREG                 (GPIO_PORTD_BASE + GPIO_O_LOCK) = GPIO_LOCK_M; // lock register

    QEIConfigure        (QEI0_BASE,
        (QEI_CONFIG_CAPTURE_A | QEI_CONFIG_NO_RESET | QEI_CONFIG_QUADRATURE | QEI_CONFIG_NO_SWAP),
        100);

    QEIEnable (QEI0_BASE);

    // Zero the position counter
    QEIPositionSet (QEI0_BASE, 1234);
}  // QEI0_Init()

********************************************************************

    for (;;)
    {
        // Read the encoder position.
        qei_position1 = QEIPositionGet(QEI0_BASE);
.

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