DBRead bug

[Aleksey Kostromin]

Dear David!

I've discovered the following bug.

DBRead method call repeatedly returns the zero byte array.
Reading occurs every 100ms from PLC Simatic S7-317 2PN/DP.
I use snap7-bugfix-1.3.0, wrapper for .NET, x86

Best regards,
Alexey Kostromin

[Davide Nardella]

Hi Alexey,
What do you mean for returns zero byte array ? The array is filled with all zeros ?
What result code do you get from the function ?

Where is defined your array ? It's possible that the garbage collector is not aware that you are using it in unmanaged code ?

Let me know how I can reproduce the issue.
If I put a timer onto a form, in your opinion, can I reproduce the issue ? or are you using a very different schema ?

[Davide Nardella]

Hi,
I tested some configurations with subsequent read every 75-100 ms.
Using both timer and thread, and I never experienced problems (after some thousands of cycles).
I asked also to some people that are using Snap7 in .net environment for massive data transfer.

I suggest you to check your source code.

If the problem persists, please make a tiny .net program that reproduces the issue and send it me.

Regards
Dave

[Aleksey Kostromin]

Hi Davide!
Sorry, but I was mistaken. Actually when I call DBRead everything works fine. But when I call AsDBRead … WaitAsCompletion(timeout) array is filled with all zeros sometimes. Reading every 100ms occurs from another thread.
This is my code:

        Monitor.Enter(_clientLocker);

        try
        {   
            var buffer = new byte[200];

            _client.AsDBRead(199, 0, buffer.Length, buffer);

            var code = _client.WaitAsCompletion(5000);

            if (code != 0)
            {
                report("Failed to read item (" + item.name + ")! Reason: " + _client.ErrorText(code), MessageType.Fatal, true);
            }
        }
        finally
        {
            Monitor.Exit(_clientLocker);
        }

Is it correct?

Regards,
Alexey

[Davide Nardella]

So, you have a thread (not listed here) that every 100 ms calls DBRead (or AsDBRead).
I understand you correctly?

If yes, you should test the result code of AsDBRead, if it's !=0 it means that the client is busy (because it's reading the thread data).