SerialPort.BaseStream.BeginWrite & BeginRead questions

I'm having some issues trying to figure out Async communication on a serialport object and was hoping to get some help. I'm still learning Async stuff so be gentle:) 

 

I basically need to make sure that the buffer isn't full prior to writing to the serial port and also all data has been read before any more data gets written to avoid packet collision. Unfortunately the microcontro开发者_如何学运维ller that I am writing to does not have any handshaking or CTSEnabled so I have to mimic it in code. 

 

 

public partial class Form2 : Form
{
    System.IO.Ports.SerialPort port = new System.IO.Ports.SerialPort();
    System.Timers.Timer tmrPolling = new System.Timers.Timer(200);
    static byte [] inputPacket = new byte[2] { (byte)255, (byte)0 }; // Byte to send to SerialPort when input polling timer is activated.

    AsyncCallback callback;
    IAsyncResult result;

    Form2()
    {
        InitializeComponent();
        port.PortName = "COM9";
        port.BaudRate = 38400;
        port.DataBits = 8;
        port.StopBits = System.IO.Ports.StopBits.One;
        port.Parity = System.IO.Ports.Parity.None;
        port.ReadTimeout = 1;
        port.ReceivedBytesThreshold = 5;
        port.DataReceived += new System.IO.Ports.SerialDataReceivedEventHandler(port_DataReceived);
        callback = new AsyncCallback(ReadComplete);  
        port.ReadBufferSize = (byte)60;
        port.WriteBufferSize = (byte)60;
        port.Open();  
        tmrPolling.Elapsed += new System.Timers.ElapsedEventHandler(tmrPolling_Elapsed);
    }

    void WritePacket(byte[] packet)
    {
        result = port.BaseStream.BeginWrite(packet, 0, packet.Count(), callback, port); // writes the input packet to the SerialPort - needed to read the IO values
    }

    void ReadComplete(IAsyncResult result)
    {

    }


    void tmrPolling_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
    {  
        WritePacket(inputPacket); // writes the input packet to the SerialPort - needed to read the IO values
    }

    void port_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
    {
        port.BaseStream.EndWrite(result);
        // Reads the data coming in from the serial port and calls the thread safe delegate to update the values on the form.
        byte [] received = new byte[port.BytesToRead];
        result = port.BaseStream.BeginRead(received, 0, received.Count(), callback, port);
        port.BaseStream.EndRead(result);  
    }

    private void UpdateValues()
    {
        byte[] b = new byte[] { (byte)255, (byte)6, (byte)hsbPan.Value, (byte)vsbTilt.Value, (byte)0,  
        (byte)0, (byte)0, (byte)0, (byte)13, (byte)10 };
        WritePacket(b);
    }

    private void chkEnablePolling_CheckedChanged(object sender, EventArgs e)
    {  
        tmrPolling.Enabled = chkEnablePolling.Checked;
        test.Enabled = chkEnablePolling.Checked;
        vsbInputInterval.Enabled = chkEnablePolling.Checked;
        vsbInputInterval.Value = Convert.ToInt32(tmrPolling.Interval);
        txtInputInterval.Enabled = chkEnablePolling.Checked;
        txtInputInterval.Text = ((float)tmrPolling.Interval / ( float)1000).ToString() + " sec";
    }

    private void vsbInputInterval_Scroll(object sender, ScrollEventArgs e)
    {
        // adjusts the tick frequency of the Timer for input polling. 
        txtInputInterval.Text = ((float)tmrPolling.Interval / (float)1000).ToString() + " sec";
        tmrPolling.Interval = vsbInputInterval.Value;
    } 

    private void vsbTilt_Scroll(object sender, ScrollEventArgs e)
    {  
        UpdateValues();
    }

    private void hsbPan_Scroll(object sender, ScrollEventArgs e)
    {
        UpdateValues();
    }
}