What is the function lwIPHostTimerHandler() in Tiva C 1294 LauchPad project?

Hi,

I import project enet_Iwip for Tiva C 1294 LaunchPad. In the UART window, it displays:

Ethernet IwIP example

Waiting for IP.

Waiting for link.

I do not find any file describes the meaning of the above lines.

The following function writes the above message, but I don't see the purpose of it yet. Could you explain it to me,

or point to a link to tell the things. I don't know whether there are other modifications or something else on the project.

Thanks,

//*****************************************************************************
//
// Required by lwIP library to support any host-related timer functions.
//
//*****************************************************************************
void
lwIPHostTimerHandler(void)
{
    uint32_t ui32Idx, ui32NewIPAddress;

    //
    // Get the current IP address.
    //
    ui32NewIPAddress = lwIPLocalIPAddrGet();

    //
    // See if the IP address has changed.
    //
    if(ui32NewIPAddress != g_ui32IPAddress)
    {
        //
        // See if there is an IP address assigned.
        //
        if(ui32NewIPAddress == 0xffffffff)
        {
            //
            // Indicate that there is no link.
            //
            UARTprintf("Waiting for link.\n");
        }
        else if(ui32NewIPAddress == 0)
        {
            //
            // There is no IP address, so indicate that the DHCP process is
            // running.
            //
            UARTprintf("Waiting for IP address.\n");
        }
        else
        {
            //
            // Display the new IP address.
            //
            UARTprintf("IP Address: ");
            DisplayIPAddress(ui32NewIPAddress);
            UARTprintf("\nOpen a browser and enter the IP address.\n");
        }

        //
        // Save the new IP address.
        //
        g_ui32IPAddress = ui32NewIPAddress;

        //
        // Turn GPIO off.
        //
        MAP_GPIOPinWrite(GPIO_PORTN_BASE, GPIO_PIN_1, ~GPIO_PIN_1);
    }

    //
    // If there is not an IP address.
    //
    if((ui32NewIPAddress == 0) || (ui32NewIPAddress == 0xffffffff))
    {
        //
        // Loop through the LED animation.
        //

        for(ui32Idx = 1; ui32Idx < 17; ui32Idx++)
        {

            //
            // Toggle the GPIO
            //
            MAP_GPIOPinWrite(GPIO_PORTN_BASE, GPIO_PIN_1,
                    (MAP_GPIOPinRead(GPIO_PORTN_BASE, GPIO_PIN_1) ^
                     GPIO_PIN_1));

            SysCtlDelay(g_ui32SysClock/(ui32Idx << 1));
        }
    }
}