topic Re: Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library in Components

Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library

Christian_L — Thu, 23 Jul 2009 15:18:17 GMT

Please post your questions, feedback, and comments on the Queue Message Handler and Asynchronous Message Communication reference library here.

Message Edited by Christian L on 07-23-2009 10:18 AM

Re: Queued Message Handler (QMH) Design Pattern and Reference Library

_Chris — Thu, 19 Feb 2009 14:27:03 GMT

Why a Windows only package ?

Re: Queued Message Handler (QMH) Design Pattern and Reference Library

Christian_L — Fri, 20 Feb 2009 16:23:10 GMT

Chris,

Could you outline for me what it would take to publish the QMH for other platforms? I have attached an OpenG package that can be used with VIPM (at least on Windows).

You need to rename the attached ZIP file to "nise_lib_qmh-1.0.7-1.ogp" as DevZone currently does not allow *.ogp files.

Message Edited by Christian L on 02-20-2009 10:23 AM

Re: Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library

ssingh1 — Tue, 28 Jul 2009 14:51:58 GMT

Please post download for Labview Version 8.2 also.

Re: Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library

Christian_L — Tue, 28 Jul 2009 21:24:27 GMT

Attached are the VIs saved back to LabVIEW 8.0. There will be some broken VIs when you first open the examples and library VIs as the code released on DevZone does use some newer features in LabVIEW which did not exist in LV 8.0, but these should be pretty easy to correct.

Re: Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library

ssingh1 — Wed, 29 Jul 2009 06:00:09 GMT

Dear Christian,

Thanks for your quick reply.

I will check the Vi's and let you know.

Shourya

Re: Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library

ssingh1 — Wed, 29 Jul 2009 12:04:14 GMT

Dear Christian,

The Library is working and examples too can be correctly very easily.

Thanks

Shourya

Re: Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library

wireman — Thu, 18 Feb 2010 22:58:29 GMT

The AMC Send Message and AMC Dispatcher apparently send message data by formatting to XML and parsing the resulting data via user.lib\AMC\subVIs\amc_Format XML.vi and user.lib\AMC\subVIs\amc_Parse XML.vi. It's not clear to me why the architecture makes use of XML at this level. It is true that the calling VIs don't care how this implemented--unless you are trying to send and receive characters that are normally reserved for XML, such as <> or "". Unfortunately, there does not seem to be a way to escape these special characters.

Incidentally, if you send a message that uses the special characters,

e.g. A diagnostic message such as

"" is not a valid cmd

the user.lib\AMC\AMC Send Message.vi does not throw and error or warning and the Dispatcher on the other side filters out the message and you don't see an error or warning there either.

It seems to me that the messages should be formatted in a such a way so that any kind of data can be sent through the mechanism without regard for the formatting that is done to it. i.e. I should be able to send any string value in one end and expect to get it verbatim on the receiving side.

-Nate

Re: Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library

Christian_L — Thu, 04 Mar 2010 16:17:43 GMT

Nate,

Thanks for the feedback. I choose XML initially because I wanted an open protocol that could be easily implemented and supported in other programming languages. i.e. I want AMC to be able to communicate between LabVIEW and an application developed in C. I agree that it needs to do better error checking if the data contained in the message will cause a problem in the XML parsing. I will add this to the list for the next update and see if we can support any arbitary strings or binary objects. It may require the use of an alternate underlying transport protocol.

Re: Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library

wireman — Thu, 04 Mar 2010 18:56:15 GMT

Christian,

Thanks for your response. Since we do not have requirements for working with C code, we modified our AMC to use the LabVIEW flatten and unflatten. Thanks for making it for us and allowing it to be open source so that we can do this!

-Nate

Re: Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library

Changi — Tue, 20 Apr 2010 12:00:15 GMT

Hello,

I have used the AMC library as suggested in the 'Reference design for Real time test' in this thread. The problem I am facing is that when I send a message from target to host, it takes a really long time (4-5 seconds approx) to reach the host. My time deterministic loop on target runs at around 1 ms. Hence, this performance is not acceptable at all.

Is this kind of performance expected with the AMC library?

Thanks,

Aditya Changavalli

LabVIEW 2009

LV RT 9.0

Re: Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library

Changi — Tue, 20 Apr 2010 15:35:44 GMT

Just to add to the above question, I did a few tests and the time taken for a message to reach the target from host is 10 ms approx while the time taken from host to target is 4500ms!!

I used the exact same VI design for both directions. Can someone please tell me why this is happening?

Aditya Changavalli

LabVIEW 2009

LV RT 9.0

Re: Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library

wireman — Tue, 20 Apr 2010 15:45:33 GMT

Aditya,

I'm not sure why it's happening. We have not seen that problem here. Have you tried using any of the sample projects to see if they exhibit the symptoms that you are seeing?

-Nate

Re: Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library

Changi — Wed, 21 Apr 2010 08:22:18 GMT

Hey Nate,

Thanks for replying. I am not sure where to find the sample AMC projects. I tried to use the examples that come with the library. But, I was facing some problems since I changed the type-def of the message (just removed the message attributes) as suggested in the AMC tutorial.

Besides, I tried to send just a simple UDP message (without AMC) across from Target to Host and its received almost instantaneously. I just cannot figure out where the delay is coming from!

Aditya Changavalli

Re: Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library

wireman — Wed, 21 Apr 2010 14:17:08 GMT

Aditya,

The ones I am thinking of are the Reference Applications linked from the bottom of this page: A Reference Architecture for Local Machine Control

in the Machine Control Architecture Content diagram. Click on the "A Simple Machine Control Example".

You will also need to download and install a bunch of the other Reference Libraries.

-Nate

Re: Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library

Changi — Wed, 21 Apr 2010 14:51:12 GMT

Nate,

I have already used the reference applications from this page: Reference Design for Real Time Test. This too had a bunch of other libraries. I modeled my use of AMC library exactly as given in this one.

I did some more test and the problem seems to come from the fact that my host computer has two network connections, while the target has one.

In fact, when I disable one network connection (not the one I connect to target), I stop getting any message from target. But when both are enabled, I get the same results:

Using AMC dispatcher

1. Host --> Target : 10 ms

2. Target --> Host : 4500 ms

Using standard UDP VIs (open, read and close) on host

Target --> Host : 10 ms

I am aware that the Open UDP VI (which is called inside the AMC dispatcher) has an input terminal to specify the network address. But the results don't change whether I wire the network address to it or leave it unwired.

I feel the critical issue is the presence of multiple network connections. Any idea what is the dependency of the AMC library in such cases?

Thanks,

Aditya

Re: Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library

Changi — Thu, 22 Apr 2010 13:40:44 GMT

I used Wireshark to tap the network messages and the problem gets stranger still. Using AMC dispatcher, though I get the message from the target instantaneously, there are some "Name Query" over NBNS (NetBIOS) protocol. This causes an error "Destination Unreachable - Port unreachable" for the next 4500 ms. The AMC dispatcher does not stop executing till that time and hence does nto update the message received.

This problem is completely absent when I use UDP VIs. There are no NBNS queries and consequently no error messages. Hence, I get the message immediately.

For now, I got around the problem by disabling NetBIOS over TCP/IP in the WINS tab of advanced TCP/IP properties dialog box. I had to do this for both the network connections. Now, even AMC dispatcher gives instantaneous results.

What I don't understand however is why the AMC dispatcher is sending NBNS queries to the target? I could not find anything like that in its code.

Its particularly serious as I want to protect future users of my developed Real time VIs to be protected against such unpredictable behaviour. I might have to re-consider using AMC. Please help!!

- Aditya Changavalli

LabVIEW 2009

LV RT 9.0

Re: Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library

Christian_L — Thu, 22 Apr 2010 16:03:55 GMT

Aditya,

Thank you for digging into this more and posting your results. I have not had a chance to test and reproduce this with a low level Ethetnet monitor, but I'm pretty sure that the NetBIOS call you see is initiated by the IP to String function in amc_Dispatch Read and Process UDP Messages.vi in the Dispatcher. This function is used to convert an IP address stored as a U32 to a string, either as Dot notation or as the name of the other device. For conversion to dot notation the function should not need to go out on the network, but it seems that it does. I will look into this more.

You can easily replace this function with a little LV code to do the conversion without this function and the associated network traffic.

Re: Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library

Changi — Fri, 23 Apr 2010 09:16:51 GMT

Christian,

Thank you! It solves a big mystery, but it was fun trying to figure it out.

If it helps you, I have attached a screenshot of the trace monitored, along with the trace file (Wireshark format 'pcap').

Thanks again for the AMC Library. It works like a charm 🙂

Aditya

PS - The NetBIOS problem is there in other LabVIEW palettes too, as I found out with the FTP transfer VI. But now I know why!

Re: Queued Message Handler (QMH) and Asynchronous Message Communication (AMC) Reference Library

Pellerin — Wed, 01 Dec 2010 09:14:18 GMT

Hi,

I am trying to install amc on my computer, but get the message "You must install LabVIEW 8.5 or later on the system before you can run this setup". I get the same message when I try to install some of the other required files, but not for all. I guess it maybe has to do with the fact that I have 64 bits LabVIEW (2010), because it worked when I had the 32 bits version. What should I do?