MFC UDP Serial Sample

Introduction

This sample demonstrates how to write a UDP serial application using the MFC socket architecture to communicate with a device server.

For the purpose of this demonstration, the sample application creates a networking socket it uses to send and receive serial data encapsulated in UDP datagrams from the device server. The device server uses its UDP Serial Client and Server features, and a loopback plug to relay data received on its first port back to the sample application.

Device Server Setup

This sample was designed to operate with the first port on the device server, and requires that the port be configured with UDP Client and Server information. After the device server is configured properly, the port must also have a loopback plug attached to it.
Configure the device server

Access the web interface by entering the module’s IP address in a browser’s URL window.

Choose Serial Ports from the Configuration menu.

Configure the module as a UDP server by doing the following:

Click the UDP tab.

Check Enable UDP Server.

Specify 2101 as the Raw UDP port.

Click Save.

Configure the module as a UDP client by doing the following:

Click Enable UDP Client.

Configure a destination by doing the following (1) Supplying the IP address of the PC on which the sample application is installed. (2) Supplying a UDP port of 7777. (3) Ensuring that the Enabled field is checked.

Click Save.

Connect the loopback plug to port 1.

How To Build

This sample has been written and tested with Microsoft Visual C++® 6.0. It contains a Developer Studio project file (.dsp), that can be opened in the development environment for editing and compiling.
To build this sample from within Microsoft Visual C++® 6.0

Select File > Open Workspace... from the main menu.

Change Files of type: to Projects (.dsp).

Locate and open the .dsp file for this sample.

Select Build > Rebuild All menu items to compile the sample.

Step-by-Step

1. Initialize Windows Sockets

The following initialization code should be in the main CWinApp derived object's overridable InitInstance function.
if (!AfxSocketInit())
{
   AfxMessageBox(IDP_SOCKETS_INIT_FAILED);
   return FALSE;
}
Initializing Windows Sockets is critical. Failing to initialize Windows Sockets will cause all other socket function calls to fail.

2. Create a local socket

The call to create a socket looks like this:
m_MySocket.Create(7777, SOCK_DGRAM)
In this sample, the socket is represented by the CAsyncSocket derived class CMySocket. An object of CMySocket type is declared as a private member variable of the main dialog class and named m_MySocket.

m_MySocket is unusable until its Create member function is called, which is done in the main dialog's OnInitDialog overridable function. Since this sample demonstrates using a UDP socket that sends and receives data, a well-known port (7777) and datagram socket type (SOCK_DGRAM) are both supplied to the call to Create. The remaining default parameters of the Create function are sufficient for the application's purposes.

3. Transmit data

Transmitting data is done by calling the socket's SendTo member functions.
m_MySocket.SendTo(Data, Length,
                  PortToSendTo, AddressToSendTo);
The SendTo member function is used on connectionless UDP sockets to transmit a datagram to a specific peer. The parameters supplied are: Data which is a pointer to a buffer containing the data to transmit, Length which is the number of bytes of data in the buffer, and PortToSendTo and AddressToSendTo which are the port number and IP address of the device server that should receive the data. For Digi device servers, the UDP port number for Port 1 is 2101

4. Receive data

To retrieve data, the socket's ReceiveFrom member function is called.
m_MySocket.ReceiveFrom(Data, sizeof(Data),
                       AddressReceivedFrom,
                       PortReceivedFrom);
In the function call the sample provides a buffer (Data) to store the incoming data, the length (sizeof(Data)) of that buffer in bytes, and locations (AddressReceivedFrom and PortReceivedFrom) to store the IP address and port number of the device server that sent the data.

With the device server setup with the loopback plug, the data transmitted in the step above will be sent directly back to the sample application. The socket is notified that data has arrived for it when it receives the OnReceive notification.

5. Close the socket

Accomplish this task by calling the following two functions:
m_MySocket.ShutDown(CAsyncSocket::both);
m_MySocket.Close();
When the sample application is done using the socket, the connection it represents must be terminated properly (ShutDown) and any resources it may be using should be released (Close).