2 replies to this topic

[ukkiwisurfer]

Following on from Chris' comments about waiting for a network connection on the Wifi version of the Netduino 3, I've written a Network helper class to use for both the Ethernet and Wifi boards:

 

 public NetworkInformation GetNetworkDetails(int interfaceIndex)

 {

     NetworkInformation information = null;

 

     NetworkChange.NetworkAvailabilityChanged += OnNetworkAvailabilityChanged;

     NetworkChange.NetworkAddressChanged += OnNetworkAddressChanged;

 

     // Wait for the network to become availableand for a DHCP address to be allocated.

     WaitHandle.WaitAll(new[] { m_WaitForAddressChange, m_WaitForNetwork });

....

}

 

The Ethernet version is configured to use DHCP. For reference the associated code to enable the WaitHandle.WaitAll() is below.

 

        /// <summary>

        /// Initialises an instance of the <see cref="NetworkHelper"/> class.

        /// </summary>

        public NetworkHelper()

        {

            m_WaitForNetwork = new AutoResetEvent(false);

            m_WaitForAddressChange = new AutoResetEvent(false);

        }

 

        /// <summary>

        /// Event handler to signal when the network address has changed.

        /// </summary>

        /// <param name="sender"></param>

        /// <param name="eventArgs"></param>

        private void OnNetworkAddressChanged(object sender, EventArgs eventArgs)

        {

            m_WaitForAddressChange.Set();

        }

 

        /// <summary>

        /// Event handler to signal that the network is now available.

        /// </summary>

        /// <param name="sender"></param>

        /// <param name="networkAvailabilityEventArgs"></param>

        private void OnNetworkAvailabilityChanged(object sender, NetworkAvailabilityEventArgs eventArgs)

        {

            if (eventArgs.IsAvailable)

            {

                m_WaitForNetwork.Set();

            }

        }

[ukkiwisurfer]

In an interesting twist to this issue, running this code on a Netduino Plus 2 highlights a race condition. The issue is that the ethernet and Wifi networking capabilities on the Netduino 3 take a lot longer to initialise (3+ seconds) than the Netduino Plus 2's (4.3.2.1 Firmware) Ethernet does (milliseconds).

 

The consequence is, the above code will block indefinitely on Netduino Plus 2 at the WaitHandle.WaitAll() call because the NetworkChange event handlers never trigger. The network has already been initialised and configured (DHCP) even before the code has had a chance to set up the event handlers.

 

However the Netduino 3 (Ethernet and Wifi) take several seconds to initialise, allowing the NetworkChange event handlers to be set up and to fire.

[ukkiwisurfer]

The following code should remedy the above issue for the Netduino Plus 2 and will still work for the Netduino 3 (Ethernet and Wifi) boards. Short summary: specify a timeout in milliseconds and loop until the DHCP address has been assigned.

 

/// <summary>
/// Returns the IP address of the device.
/// </summary>

public NetworkInformation GetNetworkDetails(int interfaceIndex)
{
           NetworkInformation information = null;

           // Set up event handlers for network state changes.
           NetworkChange.NetworkAvailabilityChanged += OnInternalNetworkAvailabilityChanged;
           NetworkChange.NetworkAddressChanged += OnNetworkAddressChanged;

           try
           {
               // Wait for the network to become available and for a DHCP address to be allocated.
               bool isWaitingToInitialise = true;
               while (isWaitingToInitialise)
               {
                   var isSignalled = WaitHandle.WaitAll(new[] { m_WaitForAddressChange, m_WaitForNetwork }, m_WaitForNetworkEventInMilliseconds, false);
                   if (!isSignalled)
                   {
                       // Retrieve network interface details to see if the initialisation had already occurred.
                       information = QueryInterface(interfaceIndex);
                       if ((information.IsDHCPEnabled) && (information.IpAddress != "0.0.0.0"))
                       {
                           isWaitingToInitialise = false;
                       }
                   }
                   else isWaitingToInitialise = false;
               }

               information = QueryInterface(interfaceIndex);
           }
           finally
           {
               m_WaitForAddressChange.Reset();
               m_WaitForNetwork.Reset();
           }

           return information;
       }

       /// <summary>
       /// Queries a network device for details about its connection state.
       /// </summary>
       /// <param name="interfaceIndex">
       /// The index of the device to query.
       /// </param>
       /// <returns>
       /// The status information on the network device.
       /// </returns>
       public NetworkInformation QueryInterface(int interfaceIndex)
       {
           NetworkInformation information = null;

          
               var networkInterface = GetInterface(interfaceIndex);
               if (networkInterface != null)
               {
                   // Then capture the network details. 
                   information = new NetworkInformation();
                   information.IpAddress = networkInterface.IPAddress;
                   information.IsDHCPEnabled = networkInterface.IsDhcpEnabled;
                   information.SubnetMask = networkInterface.SubnetMask;
                   information.MacAddress = networkInterface.PhysicalAddress;
                   information.NetworkInterfaceType = networkInterface.NetworkInterfaceType.ToString();
               }

           return information;
       }