Question

I’m working on an ASP.NET website in which I’ll need to access an usb device from the client side.

I’ve seen that Silverlight 5, through the use of P/Invoke, allows us to access dlls on the client machine. I plan to add a silverlight control in one of my page that will interact with my usb Device. This, way, each customer using this kind of device, will only need to connect on my website and start working with it.

Nonetheless, being a beginner at that kind of interaction with an usb device, how can I manage to do this ?

Which windows dll will provide me with a good way of interacting with an usb device ?

Further informations :

• I need to be able to communication through COM port. A typical serial communication. How can I manage to do this ?

For testing purpose, I can connect to my device through an application like “Hercules”, and I basically need to reprodure that kind of connection in my silverlight module…

Do you guys have any example ?

Thanks for your help,

Answer 1

I’ve found a wrapper class that enables me to create a connection to a serial port within Silverlight 5. I’m now able to access my usb device, through a serial communication.

Since I spent lot of time trying to make it work, I’ll share this class with you :

using System;
using System.IO;
using System.Runtime.InteropServices;
using System.Text;

namespace TestSerialDLL
{
  public class SerialWrapper : IDisposable
  {
    #region Enum
    public enum StopBits
    {
      None,
      One,
      Two,
      OnePointFive,
    }

    public enum Parity
    {
     None,
      Odd,
      Even,
      Mark,
      Space,
    }
    #endregion
    #region Fields
    /// <summary>
    /// The baud rate at which the communications device operates.
    /// </summary>
    private readonly int iBaudRate;

    /// <summary>
    /// The number of bits in the bytes to be transmitted and received.
    /// </summary>
    private readonly byte byteSize;

    /// <summary>
    /// The system handle to the serial port connection ('file' handle).
    /// </summary>
    private IntPtr pHandle = IntPtr.Zero;

    /// <summary>
    /// The parity scheme to be used.
    /// </summary>
    private readonly Parity parity;

    /// <summary>
    /// The name of the serial port to connect to.
    /// </summary>
    private readonly string sPortName;

    /// <summary>
    /// The number of bits in the bytes to be transmitted and received.
    /// </summary>
    private readonly StopBits stopBits;
    #endregion

    #region Constructor
    /// <summary>
    /// Creates a new instance of SerialCom.
    /// </summary>
    /// <param>The name of the serial port to connect to</param>
    /// <param>The baud rate at which the communications device operates</param>
    /// <param>The number of stop bits to be used</param>
    /// <param>The parity scheme to be used</param>
    /// <param>The number of bits in the bytes to be transmitted and received</param>
    public SerialWrapper(string portName, int baudRate, StopBits stopBits, Parity parity, byte byteSize)
    {
      if (stopBits == StopBits.None)
        throw new ArgumentException("stopBits cannot be StopBits.None", "stopBits");
      if (byteSize < 5 || byteSize > 8)
        throw new ArgumentOutOfRangeException("The number of data bits must be 5 to 8 bits.", "byteSize");
      if (baudRate < 110 || baudRate > 256000)
        throw new ArgumentOutOfRangeException("Invalid baud rate specified.", "baudRate");
      if ((byteSize == 5 && stopBits == StopBits.Two) || (stopBits == StopBits.OnePointFive && byteSize > 5))
        throw new ArgumentException("The use of 5 data bits with 2 stop bits is an invalid combination, " +
            "as is 6, 7, or 8 data bits with 1.5 stop bits.");

      this.sPortName = portName;
      this.iBaudRate = baudRate;
      this.byteSize = byteSize;
      this.stopBits = stopBits;
      this.parity = parity;
    }

    /// <summary>
    /// Creates a new instance of SerialCom.
    /// </summary>
    /// <param>The name of the serial port to connect to</param>
    /// <param>The baud rate at which the communications device operates</param>
    /// <param>The number of stop bits to be used</param>
    /// <param>The parity scheme to be used</param>
    public SerialWrapper(string portName, int baudRate, StopBits stopBits, Parity parity)
      : this(portName, baudRate, stopBits, parity, 8) 
    {

    }
    #endregion

    #region Open
    /// <summary>
    /// Opens and initializes the serial connection.
    /// </summary>
    /// <returns>Whether or not the operation succeeded</returns>
    public bool Open()
    {
      pHandle = CreateFile(this.sPortName, FileAccess.ReadWrite, FileShare.None,
          IntPtr.Zero, FileMode.Open, 0, IntPtr.Zero);
      if (pHandle == IntPtr.Zero) return false;

      if (ConfigureSerialPort()) return true;
      else
      {
        Dispose();
        return false;
      }
    }
    #endregion

    #region Write
    /// <summary>
    /// Transmits the specified array of bytes.
    /// </summary>
    /// <param>The bytes to write</param>
    /// <returns>The number of bytes written (-1 if error)</returns>
    public int Write(byte[] data)
    {
      FailIfNotConnected();
      if (data == null) return 0;

      int bytesWritten;
      if (WriteFile(pHandle, data, data.Length, out bytesWritten, 0))
        return bytesWritten;
      return -1;
    }

    /// <summary>
    /// Transmits the specified string.
    /// </summary>
    /// <param>The string to write</param>
    /// <returns>The number of bytes written (-1 if error)</returns>
    public int Write(string data)
    {
      FailIfNotConnected();

      // convert the string to bytes
      byte[] bytes;
      if (data == null)
      {
        bytes = null;
      }
      else
      {
        bytes = Encoding.UTF8.GetBytes(data);
      }

      return Write(bytes);
    }

    /// <summary>
    /// Transmits the specified string and appends the carriage return to the end
    /// if it does not exist.
    /// </summary>
    /// <remarks>
    /// Note that the string must end in '\r\n' before any serial device will interpret the data
    /// sent. For ease of programmability, this method should be used instead of Write() when you
    /// want to automatically execute the specified command string.
    /// </remarks>
    /// <param>The string to write</param>
    /// <returns>The number of bytes written (-1 if error)</returns>
    public int WriteLine(string data)
    {
      if (data != null && !data.EndsWith("\r\n"))
        data += "\r\n";
      return Write(data);
    }
    #endregion

    #region Read
    /// <summary>
    /// Reads any bytes that have been received and writes them to the specified array.
    /// </summary>
    /// <param>The array to write the read data to</param>
    /// <returns>The number of bytes read (-1 if error)</returns>
    public int Read(byte[] data)
    {
      FailIfNotConnected();
      if (data == null) return 0;

      int bytesRead;
      if (ReadFile(pHandle, data, data.Length, out bytesRead, 0))
        return bytesRead;
      return -1;
    }

    /// <summary>
    /// Reads any data that has been received as a string.
    /// </summary>
    /// <param>The maximum number of bytes to read</param>
    /// <returns>The data received (null if no data)</returns>
    public string ReadString(int maxBytesToRead)
    {
      if (maxBytesToRead < 1) throw new ArgumentOutOfRangeException("maxBytesToRead");

      byte[] bytes = new byte[maxBytesToRead];
      int numBytes = Read(bytes);
      //string data = ASCIIEncoding.ASCII.GetString(bytes, 0, numBytes);
      string data = Encoding.UTF8.GetString(bytes, 0, numBytes);
      return data;
    }
    #endregion

    #region Dispose Utils
    /// <summary>
    /// Disconnects and disposes of the SerialCom instance.
    /// </summary>
    public void Dispose()
    {
      if (pHandle != IntPtr.Zero)
      {
        CloseHandle(pHandle);
        pHandle = IntPtr.Zero;
      }
    }

    /// <summary>
    /// Flushes the serial I/O buffers.
    /// </summary>
    /// <returns>Whether or not the operation succeeded</returns>
    public bool Flush()
    {
      FailIfNotConnected();

      const int PURGE_RXCLEAR = 0x0008; // input buffer
      const int PURGE_TXCLEAR = 0x0004; // output buffer
      return PurgeComm(pHandle, PURGE_RXCLEAR | PURGE_TXCLEAR);
    }
    #endregion

    #region Private Helpers
    /// <summary>
    /// Configures the serial device based on the connection parameters pased in by the user.
    /// </summary>
    /// <returns>Whether or not the operation succeeded</returns>
    private bool ConfigureSerialPort()
    {
      DCB serialConfig = new DCB();
      if (GetCommState(pHandle, ref serialConfig))
      {
        // setup the DCB struct with the serial settings we need
        serialConfig.BaudRate = (uint)this.iBaudRate;
        serialConfig.ByteSize = this.byteSize;
        serialConfig.fBinary = 1; // must be true
        serialConfig.fDtrControl = 1; // DTR_CONTROL_ENABLE "Enables the DTR line when the device is opened and leaves it on."
        serialConfig.fAbortOnError = 0; // false
        serialConfig.fTXContinueOnXoff = 0; // false

        serialConfig.fParity = 1; // true so that the Parity member is looked at
        switch (this.parity)
        {
          case Parity.Even:
            serialConfig.Parity = 2;
            break;
          case Parity.Mark:
            serialConfig.Parity = 3;
            break;
          case Parity.Odd:
            serialConfig.Parity = 1;
            break;
          case Parity.Space:
            serialConfig.Parity = 4;
            break;
          case Parity.None:
          default:
            serialConfig.Parity = 0;
            break;
        }
        switch (this.stopBits)
        {
          case StopBits.One:
            serialConfig.StopBits = 0;
            break;
          case StopBits.OnePointFive:
            serialConfig.StopBits = 1;
            break;
          case StopBits.Two:
            serialConfig.StopBits = 2;
            break;
          case StopBits.None:
          default:
            throw new ArgumentException("stopBits cannot be StopBits.None");
        }

        if (SetCommState(pHandle, ref serialConfig))
        {
          // set the serial connection timeouts
          COMMTIMEOUTS timeouts = new COMMTIMEOUTS();
          timeouts.ReadIntervalTimeout = 1;
          timeouts.ReadTotalTimeoutMultiplier = 0;
          timeouts.ReadTotalTimeoutConstant = 0;
          timeouts.WriteTotalTimeoutMultiplier = 0;
          timeouts.WriteTotalTimeoutConstant = 0;
          if (SetCommTimeouts(pHandle, ref timeouts))
          {
            return true;
          }
          else
          {
            return false;
          }
        }
        else
        {
          return false;
        }
      }
      else
      {
        return false;
      }
    }

    /// <summary>
    /// Helper that throws a InvalidOperationException if we don't have a serial connection.
    /// </summary>
    private void FailIfNotConnected()
    {
      if (pHandle == IntPtr.Zero)
        throw new InvalidOperationException("You must be connected to the serial port before performing this operation.");
    }
    #endregion

    #region Native Helpers
    #region Native structures
    /// <summary>
    /// Contains the time-out parameters for a communications device.
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    struct COMMTIMEOUTS
    {
      public uint ReadIntervalTimeout;
      public uint ReadTotalTimeoutMultiplier;
      public uint ReadTotalTimeoutConstant;
      public uint WriteTotalTimeoutMultiplier;
      public uint WriteTotalTimeoutConstant;
    }

    /// <summary>
    /// Defines the control setting for a serial communications device.
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    struct DCB
    {
      public int DCBlength;
      public uint BaudRate;
      public uint Flags;
      public ushort wReserved;
      public ushort XonLim;
      public ushort XoffLim;
      public byte ByteSize;
      public byte Parity;
      public byte StopBits;
      public sbyte XonChar;
      public sbyte XoffChar;
      public sbyte ErrorChar;
      public sbyte EofChar;
      public sbyte EvtChar;
      public ushort wReserved1;
      public uint fBinary;
      public uint fParity;
      public uint fOutxCtsFlow;
      public uint fOutxDsrFlow;
      public uint fDtrControl;
      public uint fDsrSensitivity;
      public uint fTXContinueOnXoff;
      public uint fOutX;
      public uint fInX;
      public uint fErrorChar;
      public uint fNull;
      public uint fRtsControl;
      public uint fAbortOnError;
    }
    #endregion

    #region Native Methods
    // Used to get a handle to the serial port so that we can read/write to it.
    [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
    static extern IntPtr CreateFile(string fileName,
       [MarshalAs(UnmanagedType.U4)] FileAccess fileAccess,
       [MarshalAs(UnmanagedType.U4)] FileShare fileShare,
       IntPtr securityAttributes,
       [MarshalAs(UnmanagedType.U4)] FileMode creationDisposition,
       int flags,
       IntPtr template);

    // Used to close the handle to the serial port.
    [DllImport("kernel32.dll", SetLastError = true)]
    static extern bool CloseHandle(IntPtr hObject);

    // Used to get the state of the serial port so that we can configure it.
    [DllImport("kernel32.dll")]
    static extern bool GetCommState(IntPtr hFile, ref DCB lpDCB);

    // Used to configure the serial port.
    [DllImport("kernel32.dll")]
    static extern bool SetCommState(IntPtr hFile, [In] ref DCB lpDCB);

    // Used to set the connection timeouts on our serial connection.
    [DllImport("kernel32.dll", SetLastError = true)]
    static extern bool SetCommTimeouts(IntPtr hFile, ref COMMTIMEOUTS lpCommTimeouts);

    // Used to read bytes from the serial connection.
    [DllImport("kernel32.dll")]
    static extern bool ReadFile(IntPtr hFile, byte[] lpBuffer,
       int nNumberOfBytesToRead, out int lpNumberOfBytesRead, int lpOverlapped);

    // Used to write bytes to the serial connection.
    [DllImport("kernel32.dll", SetLastError = true)]
    static extern bool WriteFile(IntPtr hFile, byte[] lpBuffer,
        int nNumberOfBytesToWrite, out int lpNumberOfBytesWritten, int lpOverlapped);

    // Used to flush the I/O buffers.
    [DllImport("kernel32.dll", SetLastError = true)]
    static extern bool PurgeComm(IntPtr hFile, int dwFlags);
    #endregion
    #endregion
  }
}

Here is an Example of the SerialWrapper in action:

using (var p = new SerialWrapper(@"\\.\COM12", 9600, SerialWrapper.StopBits.One, SerialWrapper.Parity.None))
{
    if (!p.Open())
    {
        Console.WriteLine("Unable to connect."); 
        return;
    }
    while (true)
    {
        Console.Write(p.ReadString(1024));
    }
}