Differences in Speed Results using MessageBasedSessionReader and MessageBasedSession.

[friday]

I have a speed test using a raw socket connection that causes an instruments to return a large buffer (43000 bytes of data). Each line of data returns a 43 bytes that includes "#0", 10 floats, and a '\n' character.

I'm using C# in Microsoft Visual Studio .NET 2005 to read the data in a loop. There are two test cases to read the data. (mSession is a MessageBasedSession object). In the first case, data is read using mSession.ReadByteArray(43). In the second case, MessageBasedSessionReader methods are used to read the data.

                ....
                MessageBasedSessionWriter lWriter = new MessageBasedSessionWriter(mSession);
                MessageBasedSessionReader lReader = new MessageBasedSessionReader(mSession);
                ...
                ...
                for (int j = 0; j < lNumPoints10; ++j) // lNumPoints = 1000
                {
                    if(lTestType == 1)
                   {
                        mSession.ReadByteArray(43);
                    }
                   else
                   {
                        lChar[0] = lReader.ReadChar(); // Read '#'
                        lChar[1] = lReader.ReadChar(); // Read '0'
                        lData = lReader.ReadSingles(10);
                        lChar[2] = lReader.ReadChar(); // Read '\n'*
                    }
                }

I've verified the data returned is correct in both cases. Yet, there is a huge performance hit using the higher level functions of lReader instead of mSession. If fact the time hit is related to the Timeout property of mSession as it takes exactly 2 seconds longer to receive the data in the second case (Changing the timeout property changes the result). But, a timeout exception is not being intercepted by my code.

Any idea to why this would happen?

[MissyS]

Hi,

What version of NI-VISA are you using? Here is a link to the current version of VISA.

Can you post a NI-Spy capture for each of these two cases? The simpler the test program captured can hopefully help us narrow down the cause of this problem. Thanks!

Regards,

[friday]

I'm using the latest version, VISA 4.0.

Attached are a copy of the captures. Basically, a script is downloaded to my unit. After s1() is sent, the script executes, and the unit returns the string "End" when complete.  Even though I'm reading 4 characters in each case, the MessageBasedSessionReader takes longer.

[friday]

Regarding my last post, this test is slightly different from the first I posted, but the results are the same. The first test read a binary number, while this test merely looks for the string "End."

In my code, I have the following to read the return data.

#if USE_MESSAGE_READER
mReader.ReadChars(4);
 #else
mSession.ReadByteArray(4);
#endif

[MissyS]

Hi,

I was able to reproduce the issue you are seeing. I noticed from the NI-Spy capture you posted that the MessageBasedSessionReader's viRead (the VISA read) command was timing out. I will investigate this issue further and let you know what I find.

Regards,