Question

I’m writing a software that communicates with 4 devices via serial port. One of them, Input/output module (ICP CON) has 4 input channels (DL) and 4 output channels (RL). I need to monitor status of DL channels and then, when a signal is detected I have to do some processing, which depends on which signal has been detected.

I’m calling 4 methods asynchronously, every 500ms (timer), here’s the tick event:

//stop the timer
timer1.Stop();

//open com port 2
Tester.Devices.ICP.OpenICPPort(2, 9600);

//dl 0
ic = new CheckDLStatus(0, this);
ic.Execute();

//dl 1
ic = new CheckDLStatus(1, this);
ic.Execute();

//dl 2
ic = new CheckDLStatus(2, this);
ic.Execute();

//dl3 
ic = new CheckDLStatus(3, this);
ic.Execute();

//close com port 2
Tester.Devices.ICP.CloseICPPort(2);

//enable the timer again
timer1.Enabled = true;

public CheckDLStatus(int DL, Form1 F1)
{
    //form 1 instance
    f1 = F1;

    // setup the delegate to call
    switch (DL)
    {
        case (0):
        {
            checkDL_delegate = new checkDL(
                BusinessLogicLayer.Classes.
                DevicesCommunication.CheckDl0);

            break;
        }
        case (1):
        {
            checkDL_delegate = new checkDL(
                BusinessLogicLayer.Classes.
                DevicesCommunication.CheckDl1);

                break;
        }
        case (2):
        {
            checkDL_delegate = new checkDL(
                BusinessLogicLayer.Classes.
                DevicesCommunication.CheckDl2);

                break;
        }
        case (3):
        {
            checkDL_delegate = new checkDL(
                BusinessLogicLayer.Classes.
                DevicesCommunication.CheckDl3);

                break;
        }
    }
}


public static void CheckDl2()
{
    //declare
    bool currentStatus;

    try
    {
        //input
        currentStatus = DevicesCommunication.Dl_2_On; 
        //should be false at the start of the test, 
        //so when it becomes true, the change is detected immediately

        //dl2?
        if (ICP.LookForSignal_DL2((short)2, 
            Util.Classes.Util.ResolveComPortNumber(
                Cache.settings.icpModulePort),     
            Convert.ToInt32(Cache.settings.icpModuleBaudRate)))
        {
            //signal detected
            DevicesCommunication.Dl_2_On = true;
        }
        else
        {
            //signal not detected
            DevicesCommunication.Dl_2_On = false;
        }

        //check, if status of DL2 has been changed 
        //(from true to false, from false to true)
        if (currentStatus != DevicesCommunication.Dl_2_On)
        {
            //status from before checking signal is different
            // from status read from the device so
            //status has changed

            if (DevicesCommunication.Dl_2_On)
            {
                DevicesCommunication.DL2_apperancesCounter += 1;

                //TODO
                //process
                //ProcessDL2();
            }
        }
        else
        {
            //status did not change
            //just clear buffer
            ClearBuffer();
        }

        return;
    }
    catch (Exception ex)
    {
        Util.Classes.ErrorLogging.LogError(ex, true);
        //EndCurrentTest(); 
        return;
    }
}

Execute() method, that invokes a delegate:

public void Execute()
{
    // call the method on the thread pool
    checkDL_delegate.BeginInvoke(
        this.CallBack, null);

    //checkDL_delegate.Invoke();
}

The method that is called for checking DL2 status:

public static bool LookForSignal_DL2(short DL_number, int port, int baudRate)
{
    //declare
    bool iBit;

    try
    {
        //check if there is a signal at specified Dl_number
        iBit = DCON.Read_DI_Bit(Convert.ToByte(port), 1, -1, 
            DL_number, 16, 0, 100);

        //return resposne
        return iBit; //true/false
    }
    catch (Exception ex)
    {
        Util.Classes.ErrorLogging.LogError(ex, true);
        return false;
    }
}

My problem is, when I turn on signal on DL2 channel, and I call LookForSignal_DL2 like this, without the timer and asynchronous calls (just for test):

private void button25_Click(object sender, EventArgs e)
{
    ICP.OpenICPPort(2, 9600);

    if (ICP.LookForSignal_DL2(2, 2, 9600))
    {
        MessageBox.Show("True");
    }
    else
    {
        MessageBox.Show("false!");
    }

    ICP.CloseICPPort(2);
}

It works – returns true.

If, in Execute() method I use Invoke, which makes the method call synchronous – it works (returns true), but this way I can only check 1 signal at the time.

If, in Execute() method I use BeginInvoke it doesn’t work, it returns false, even though there is signal in DL2.

I admit I don’t know what’s going on. Do you have any idea?

Answer 1

I figured it out, if it helps anyone, I made a mistake here (bold text):

//stop the timer
timer1.Stop();

//open com port 2
Tester.Devices.ICP.OpenICPPort(2, 9600);

//dl 0
ic = new CheckDLStatus(0, this);
ic.Execute();

//dl 1
ic = new CheckDLStatus(1, this);
ic.Execute();

//dl 2
ic = new CheckDLStatus(2, this);
ic.Execute();

//dl3 
ic = new CheckDLStatus(3, this);
ic.Execute();

Tester.Devices.ICP.CloseICPPort(2);

I ran my methods asynchronously, but the execution of the code went on, and everytime the port had been closed before any of the methods was able to check for signal. Unfortunetely the SDK library doesn’t return any error in that case, so it just kept returning false.

Thank you for your comments.