How to wait for a request for service (RQS)

** Note. Cross-posting on the LabVIEW forums: http://forums.ni.com/t5/LabVIEW/C-VISA-wait-on-RQS/td-p/3122939

I'm trying to write a simple C # (.NET 4.0) program to control a Keithley 2400 SMU via VISA GPIB and I'm having trouble getting the program to wait for a service request that Keithley sends at the end of a sweep.

The swing is a simple linear voltage sweep, controlled internally by the Keithley device. I have a device configured to send a ServiceRequest at the end of a sweep or when a match is reached.

I can send commands to the SMU and read the data buffer, but only if I manually enter a timeout between the sweep start command and the data read command.

One problem I am running into is that I am fairly new to C # - I am using this project (porting parts of my LV code) to find out.

Here's what I've used so far for my C # code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using NationalInstruments.VisaNS;

private void OnServiceRequest(object sender, MessageBasedSessionEventArgs e)
{
    Console.WriteLine("Service Request Received!");
}

// The following code is in a class method, but
public double[,] RunSweep()
{
    // Create the session and message-based session
    MessageBasedSession mbSession = null;
    Session mySession = null;
    string responseString = null;

    // open the address
    Console.WriteLine("Sending Commands to Instrument");
    instrAddr = "GPIB0::25::INSTR";
    mySession = ResourceManager.GetLocalManager().Open(instrAddr);

    // Cast to message-based session
    mbSession = (MessageBasedSession)mySession;

    // Here where things get iffy for me... Enabling the event and whatnot
    mbSession.ServiceRequest += new MessageBasedSessionEventHandler(OnServiceRequest);
    MessageBasedSessionEventType srq = MessageBasedSessionEventType.ServiceRequest;
    mbSession.EnableEvent(srq, EventMechanism.Handler);

    // Start the sweep (SMU was set up earlier)
    Console.WriteLine("Starting Sweep");
    mbSession.Write(":OUTP ON;:INIT");

    int timeout = 10000;             // milliseconds
    // Thread.Sleep(10000);          // using this line works fine, but it means the test always takes 10s even if compliance is hit early

    // This raises error saying that the event is not enabled.
    mbSession.WaitOnEvent(srq, timeout);

    // Turn off the SMU.
    Console.WriteLine("I hope the sweep is done, cause I'm tired of waiting");
    mbSession.Write(":OUTP OFF;:TRAC:FEED:CONT NEV");

    // Get the data 
    string data = mbSession.Query(":TRAC:DATA?");

    // Close session
    mbSession.Dispose();

    // For now, create a dummy array, 3x3, to return. The array after is the starting value.
    double[,] dummyArray = new double[3, 3] {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};

    return dummyArray;
}

      

        
        
        
      

    

All of the above should mimic this LabVIEW code:

So, any ideas on where I am going wrong?

Thank,

Edit:

After a little twisting, I found that the service request feature OnServiceRequest

actually triggered at the right time (“Service request received!” Is printed on the console).