Event structure buffering?

Hi all,
A quick question, if i have an event structure with lots of value change events for booleans, if 2 or 3 change at the same time or within a few milliseconds of each other does it buffer this event so that when it comes out of the event structure it knows another one has happened since it last went in? i.e. it could get a trigger for one, enter the event structure pass over a couple of ones that didnt trigger then get a trigger for them whilst its in it, but gone past them, then deal with the one that did trigger it and exit. Or perhaps i am not understanding how event structures process the value change triggers.
I hope i have explained myself well enough
Cheers
Mike

Pnt wrote:
Yes. As far as i know, events are buffering and it is NOT possible to miss one.
I agree here. You cannot "lose" any events. Sometimes this is a problem as demonstrated (and solved) in this old discussion:
http://forums.ni.com/ni/board/message?board.id=170&view=by_date_ascending&message.id=207811#M207811
Pnt wrote:
I agree that you should not have the same event in two different event cases (in parallel), but i disagree that there is possibility to miss an event.
LabVIEW will not allow you to place the same event in multiple event cases anyway, so there is no problem. However there is also no problem having two different event structures listening to the same event.
LabVIEW Champion . Do more with less code and in less time .

Similar Messages

Event structure doesn't handle all events from external DLL source

Hi!
I use a DLL, wich handles an USB CAN transceiver device, and generates LabVIEW user events with extcode.h and PostLVUserEvent() function.
In my vi I use an event case structure to handle theese external events. The problem is, that if the events come too frequently, then it cannot handle all events.
The vi contains a couple of parallel while loops which process the incoming data from the external event.
In another application I use the same architecture, and that works fine. This one is more complex.
Do you think I have reached the limits of the program? Or what else can be the problem?
I have tried to use a queue in the event structure, it helped a little, but yet, not all the events are handled. My external DLL sends all event, so the problem is not there.
Thanks in advance!

Hi Wasz,
Thanks for the post and I hope your well.
It is not possible for the event structure to miss events - it simply queues them up. To keep the event structure 'in time' with the code you must ensure the code to execute in each event is minimal to allow the event structure to handle the next event.
Please see this two links:
event structure buffering: leading to,
How to avoid built-up for "cursor move" events? : where somone is trying to avoid handling all events.
What sort of events are not being handled? Could it be an issue your events are not configured correctly? Maybe if you could produce a small example in LabVIEW code, so we can just test the event structure configuration... someone working around the external dll call - which you seem sure is working correctly.
In terms of queuing to process the events in other loops is certainly an option to speed up the event structure. To do this, use a produce/consumer design pattern.
hope this helps,
Kind Regards
James Hillman
Applications Engineer 2008 to 2009 National Instruments UK & Ireland
Loughborough University UK - 2006 to 2011
Remember Kudos those who help!

How to read shared variables inside event structure ?

Hi,
I have a problem that my shared variables do not update inside event structure. The program(s) I am trying to get working is seen in the attached screenshot. It works as follows:
0. I start the vi that is unsquared.
1. I write a string to a shared variable using vi in red square. I make sure that its updated using write-wait-read.
2. I run the other vi (blue square), this changes the boolean shared variable.
The unsquared vi has been running the whole time, it has event structure bind to boolean shared variable change (the one in blue vi). After I have runned the blue vi, the unsquared vi should change the indicator values to match the ones in red vi. However I have to start the blue vi multiple times to get it to change, sometimes even 6 times.
Also, when I change the value in red vi to a third value and start blue vi multiple times, the unsquared vi shows all the variables. I.e. I put "cat" to red then start red, put "mouse" to red then start red,... and then start clicking blue... Unsqured shows cat, mouse,..., dog (dog is the default).
How can I force the shared variable to update inside event sructure. I want the current value of the variable, not some historical values.
Attachments:
Screenshot-5.png ‏108 KB

Found the buffering... disabling it solved the problem... thanks.
FYI, there is another solution that I just found out... attached. Adding timeout to the event structure and the variable read outside the event structure... This makes the shared variable strings (one that is read outside and the otherone that is read inside) different.
Could someone explain why the variables are in different state even if they are used in the same place and looped with 10ms intervals?
Juha
Attachments:
Screenshot-6.png ‏110 KB

Pop-up in event structure halts execution

If I place a pop-up subVI in an event case of an event structure and this pop-up subVI contains a while loop and a stop button that would stop this while loop (thereby closing the subVI), will other events declared in the event structure be handled only after the user clicked the stop button of the subVI? If yes, is there a way for other events to be handled while the pop-up subVI is still running?
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Yes, it will stop everything in you rmain VI until the popup VI returns. The events will still be buffered, but they won't be handled by the event structure, until your pop up is closed (assuming your pop up is non-modal). If it's modal, the user won't be able to click anything at all, except controls on the pop up itself.
If you still want the user to be able to interact with your front panel while the pop up is showing, and have the FP respond, you will want to launch the popup dynamically in its own parallel process. If you are using LV 2012 you can use the start asynchronous call node. If you are using an earlier version of LabVIEW, you will have to use the "Run" method with an invoke node.
CLA, LabVIEW Versions 2010-2013

Can you share FP Controls between different Event Structures

I'm creating a program that will either read real-time data from an VNA on the GPIB bus, or read a saved s2p (Agilent) file and analyze it. The FP consists of 5 graphs, and various controls which handle events like printing, changing filters, or exiting. on the BD I have a case structure controlled by an operator selection pop-up. I tried using the same FP controls in the event structures I have setup in each case, as only one event structure would ever be executing at any given time, but the program doesn't seem to like it ast run-time. I've worked around the issue by creating "duplicate" controls and using the property setting to make them visible/disabled, etc., but the is seriously congesting my BD.
Anyone know a way to share controls with seperate event structures?

It sounds like the root problem is the overall structure of your program. I highly recommend that you check out the Queued Message Handler project template in LabVIEW 2012, that will show you how to utilize a single event structure and pass events to a consumer loop. If you program is too large to consider an architecture change at this stage of the game, then there is a workaround for your problem.
What is most likely happening is that you have the event structures all set to lock the front panel until the event completes. However the case structure that you have wrapped around these event structures is causing all but one of these event structures to be unreachable thus preventing you from handling the event. Again, as I stated above, the "RIGHT WAY" to fix this is to select a better program structure but the "kluge work-around" fix is this: Dynamically register for the value change event on all of the controls you are trying to trap events for. Dynamic events can be deregistered and re-registered at run time. This will allow only the event structure in the active owning case structure to be registered for the events, thus no other event structures will get in your way.
Disclaimer: This advice is given based on very minimal information and a great deal of speculation and may not be correct. Please include your code if you need further assistance.
Charles Chickering
Architecture is art with rules.
...and the rules are more like guidelines

Daqmx "Done" event not triggering event structure

I would like the user to be able to abort my daqmx task by pressing a button.
I am attempting to use the method in this VI:
https://decibel.ni.com/content/docs/DOC-15815
It utilizes an event structure with the daqmx Control Task VI to abort.
The example VI above works for me, on my system with my USB-6356 device, as expected.
When I attempt to incorporate the same method into my VI it does not--despite having an identical arrangement, so far as I can tell.
I believe that my problem lies with the event structure, and the dynamic registration. I am unfamiliar with this and must be using it incorrectly.
I have attached my VI, though it is cumbersome. The code which I am struggling with is in the "Acquire" case. As far as I can tell, I am doing exactly the same this in this particular case as in the example mentioned. Yet in the example, the event structure completes, or aborts, whatever you want to call it, right after the "Wait Until Done" VI executes. In my own VI, the "Wait Until Done" and "Clear Task" VIs execute, but the event structure does not register it.
Here are my specific questions: is there anything extra or special that one must do in order for the Task to properly trigger a "Done" event and pass through the event structure? At what point is the daqmx task "Done"?
thanks,
Matt
Attachments:
BoomTubeMain.vi ‏175 KB

natasftw,
My event structure is identical to theirs; what you are seeing are the two different cases that exist in the event structure. In both the example and the VI, there is a <task out>: Done and a "Dynamic Event": Value Change. In the dynamic event case, I have my abort button and relevant code--this I believe is the code you were referring to, which you thought I was missing... Regarding my multiple event structures, they should operate completely independently as they respond to different events.

Stop execution of a loop in an event structure

I tried searching the forums to avoid posting a duplicate, but most I could not open most of the vi's as they were higher version.
I put in a dummy while loop in an event structire i intend to use. Once I start executing the while loop, I am not able to stop it using a control for some reason from the fornt panel control.
I am not able to change the vale of the Stop control at all. I tried creating a seperate event for STOP, and I still could not stop the program when the While loop was executing.
I imagine I am missing something really small. I would appreciate your feedback on this.
Thanks,
Nevil
Solved!
Go to Solution.
Attachments:
FrontPanel.vi ‏34 KB

Right click on the event structure and choose "Edit Events" for the case that is giving you trouble.
Be sure the checkbox to lock the front panel is unchecked.
I suspect yours is checked, so your front panel is locked out until the event completes, thus you can never stop your loop.

Event structure in Sub VI

Hello ,
I have a developed a program which captures video and user can save images out of it. I have used .NET reference to handle the video part, and the VI is attached in this post. Now i have to make this VI as a sub VI and running this from Main VI. I tried creating event structure in Main VI which i used in sub VI , still i could not suceed. Kindly assist me in this regard
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Attachments:
Webcam-Control-Projekt-mit-Reference-Design-2013_original.zip ‏286 KB

Hello Michael,
I have attached a model in which Main VI calls the Sub VI using Event Structure. Two events can occur in Main VI and their corresponding event Structure is called in Sub VI using Register events. When i run this VI the out put is fine some times but other times i need to trigger event many times before i can see its effect in Sub VI, my doubt is that Register events are reliable, whenever (during the execution of LV) if event occurs will surely its code in the sub Vi gets executed?
also I have put a indictor(numeric) in the SUb VI which i connect back to Main VI, when i run, i can see the result only in the sub VI not in the main VI.how to see in Main VI?
I have used the this model (which is attached ) to implement my project(which i already mentioned) . one switch for starting the video and other for recording the image. The video is getting started with out any trouble, but imgae is recorded only few times when i press the button which is for image recording, most of the time second event fails to get executed. Also there are difference in output when i run with and without "Highlight execution", why this happens, is this because of Reg events?
any more info if required let me know, i will provide.
Attachments:
Main_sub_VI.zip ‏18 KB

How to make Vi file as input file in Event structure?

Hiii All..
i got problems when to construct a event structure. The file input (vi format) doesnt have source of wire connection to conect the wire (shift register) .For your information the vi that i create only contain simple mathematical equation.
I already study the New Event Handler Example. but the file input for that example (acquire data.vi) have a source of connection. anyone can help me?
thank you very much
[email protected]
Solved!
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Attachments:
TOTAL.vi ‏18 KB

Well, in your subVI you do need to wire up some inputs and outputs to your connector panel. As I said, a basic LabVIEW skill that you will find in the tutorials.
You have a number of inputs to your subVI. More than you would want to attach to a connector panel. You should perhaps use a cluster to group them together.
To get you started, here are the steps to connect a control or indicator to the connector panel.
1. Open subVI.
2. Right click on icon at upper right. Show Connector.
3. Hover over a block you want to be a connector terminal, it will change to a spool of wire. Click.
4. Go to the control or indicator on the front panel that you want to associate it with. Click again.
5. Repeat as needed for other controls and indicators and save your subVI. Now the subVI instance in your main VI can have wires connected to it.
You should plan your connector panel so that controls are on the left side of the panel, and indicators on the right. This will allow data to "flow into" and "flow out of" the subVI in a normal looking left to right orientation.

Event Structure Freezes Vi After Capturing The First Event

My Event structure catches the first instance of my button press but then it freezes my Vi. The reason is because of the while loop but I need the while loop to constantly read from a serial port and send data to a serial port. The vi included is stripped down to be just a while loop that does nothing. I have also tryed putting the event structure in the while loop, but the same thing is happening.
Any ideas?
Thanks,
Cason Clagg
SwRI
LabView 7.1, Windows XP

Also, put the button inside the event structure where it is acted upon, from LV help (suggest you read the entire events section of help):
When you trigger an event on a Boolean control configured with a latching mechanical action, the Boolean control does not reset to its default value until the block diagram reads the terminal on the Boolean control. You must read the terminal inside the event case for the mechanical action to work correctly. As a reminder, a note appears in the Edit Events dialog box when you configure a Value Change event on a latched Boolean control.
Refer to the Handling a Latched Stop Boolean Control in an Event Structure caveat for information about how to handle a latched Boolean control.
When you trigger an event on a Boolean control configured with a latching mechanical action, the Boolean control does not reset to its default value until the block diagram reads the terminal on the Boolean control. You must read the terminal inside the event case for the mechanical action to work correctly. As a reminder, a note appears in the Edit Events dialog box when you configure a Value Change event on a latched Boolean control.
Refer to the Handling a Latched Stop Boolean Control in an Event Structure caveat for information about how to handle a latched Boolean control.
~~~~~~~~~~~~~~~~~~~~~~~~~~
"It’s the questions that drive us.”
~~~~~~~~~~~~~~~~~~~~~~~~~~

How can i use the same front panel graph in more than one events in an event structure?

i want to display the signals from my sensorDAQ in a graph.but i have more than one event in the event structure to acquire the signal and display it in the graph.the first event is to acquire the threshold signals and its displayed in the graph as a feedback.after the first event is executed, i will call the second event,where the further signals are acuired and compared with the threshold signals from the event 1.my question is how can i use the same front panel control in more than two events in the event structure?please answer me i'm stuck.
Solved!
Go to Solution.

Hi,
I have attached here an example of doing the same using shift registers and local variables. Take a look. Shift register is always a better option than local variables.
Regards,
Nitzz
(Give kudos to good answers, Mark it as a solution if your problem is Solved)
Attachments:
Graph and shift registers.vi ‏12 KB
graph and local variables.vi ‏12 KB

How to use a event structure with a state machine

First, I would like to inform you that I only work on LabView part time, and have much to learn. Anything I do learn, I usually forget until I need it again, because I only work on it part time.
Using your StopWhileLoopMOD[1].vi, I am trying to put a state machine inside the event structure.
Related link: http://forums.ni.com/t5/LabVIEW/How-to-stop-while-loop-in-Event-case/td-p/465564/page/2
Here is my application: on the front panel, the user can select any combination of 7 different tests. I have created cases to perform each step of each test in the correct order, but if the user presses stop, the tests won't stop because some of the cases have a while loop inside the event structure (like you mentioned is a bad idea). The user should be able to stop the test, reselect tests to perform, and re-start the tests.
When the start button is pressed for the event structure, I need all the cases to run in the proper order, unless stop is pressed.
In the past I have indexed an array and used that to run the state machine, but it won't stop immediately.
I have sub VIs that are built in while loops because the outputs of the product needs time to stabilize.  The state machine stops and waits up to a certain number of iterations. If it passes the test, the while loop stops and the next state starts. If it takes too long, it exits and reports an error. Maybe I need to just use the state machine and not an event structure?
Is there a good example of an event structure?
metzler CLAD
Solved!
Go to Solution.

I'm not sure exactly what you are asking, but it sounds like you want to script a bunch of tests and if the user says stop, to immediately stop the current test and abandon the others? I'm going to assume that you know how to clear the array so that it will abandon the others, so I'm guessing that you are having trouble abandoning the current test? If this is indeed the case, then the problem is that you are not able to propagate the message from the main VI FP which is the GUI to the sub vi which is the test, where the test may or may not have a GUI (FP visible) of it's own. Threading was the first thing to come to mind, but this may not be necessary using events.
You can do this by passing a refnum of the stop button to the subVI, where you can then add that wait to the event case structure.
I've attached 2 VIs, mainvi.vi which is just a loop displays the count*2 (number of seconds passed since running) that will call subvi.vi and then check to see if the stop button is pressed. mainvi.vi is by no means a state engine, it is just a simple loop for demonstration purposes. subvi.vi just waits 2 seconds and leaves, it is a better structured state engine with an init state to start a poll case to wait for events and an exit state to clean up. You can modify this any way you wish to get it to do what you want. You will note that even if subvi.vi is being executed, it will terminate immediately when the stop button is pressed.
Hope this helps.
A
Attachments:
mainvi.vi ‏17 KB
subvi.vi ‏33 KB

How to use an Event Structure responding to an image control that belongs to a parent VI.

Hi
I am loading a subpanel vi by pressing a button located in the user interface of the main vi which also contains an image display. Subpanel vi opens up on the side and doesn't hide the image display of the main vi. Subpanel vi contains an event structure that needs to respond to user clicking on the image display of main vi.
Since the bug that occured while creating an image reference control isn't fixed, I am passing the main vi pane reference onto the subpanel vi. From that point I've tried to edit event structure and have it respond to the image control/pane that belongs to main vi but I don't know how.
Any help would be appreciated.
Thanks

Post a screenshot of your subVI code where you register the events.
André
Regards,
André
Using whatever version of LV the customer requires. (LV5.1-LV2012) (www.carya.nl)

Event structures used to monitor indicator change

I am new to the event structure.
Is it possible to monitor an indicator for a value change? I know this works with controls, but I'm not sure you can monitor and indicator in this way.
Thanks,
-Nathan

Yes, it's possible. However, in order to change the value so that an event will fire, you'll have to use the value(signalling) property of the indicator. It won't work if you simply wire a value to it.

Using Event Structures with Array of Clusters

Using LabVIEW 8.5
Hi all,
I'm trying to convert an existing application to one that can be used
through a touch screen. I updated the UI and added an event structure
to listen for mouse ups on controls that require a HMI keyboard or
numpad to show up. Although I've been programming for a while, I'm new
to LabVIEW and am struggling with a problem:
Is there any way to have an event case listen to an event within
arrays? I've seen a few examples on the forums, but they all start with
breaking up the arrays into individual variables. Using the variables,
they build arrays. This seems pretty tedious, and I'm pretty sure I
can't apply it to one of my arrays. Essentially, I just want to know
which cluster in which array the user has clicked on, so I can open the
HMI keyboard or numpad and send the text to that cluster. In my watered down app (Array of Clusters.vi), I've put 3 arrays of clusters and a few stand-alone controls to give you guys an idea of what I'm taking about.
BTW, I'm using the HMI Keyboard and Numpad built by the Beta Community (http://decibel.ni.com/content/docs/DOC-1062) and modified it to add a "Clear" button to the keyboard and numpad. Please let me know if I implemented this in the best way.
Thanks for the help,
Kunal
Message Edited by bhatiak on 08-04-2008 03:55 PM
Attachments:
Array of Clusters4.llb ‏274 KB

My old tic tac toe example shows how to determine which square of a 2D array has been clicked.
http://forums.ni.com/ni/board/message?board.id=170&view=by_date_ascending&message.id=247044#M247044
You probably can adapt some of it for the arrays on the right. If the array can be scrolled, you also need to account for the "indexvals" offset.
The Layers controls is easiest, because you only show one element. Just read the "index vals" property to get the array element and parse the coordinates to get the cluster element.
btw: the small while loop on the right serves no purpose at all and acts just as a CPU burner. You can delete it without any change in functionality. Is there anything else to it?
LabVIEW Champion . Do more with less code and in less time .

Event structure buffering?

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