Use event structure and while loop in parallel
Hello, I would like to use an event structure in parallel with a while loop. I have a camera that needs to constantly take pictures and I have that setup in the while loop. I also however need to do other functions in conjunction with the picture taking. I have about 50 or so events that need to have access to while the pictures are taken. Is there any way to do this? If not is there any way to have a global stop variable that is attached to all 50 of the events. I know I can do this the hard way and have each boolean event in the event structure be attached to the while loop stop control. This is however very inefficient. I would also like to know if I can simply use a mouse click as the stop of the while loop. Am I able to have a variable that goes from false to true on mouse click without using the event structure to do this? Thanks.
Yes, just place the event structure in a second while loop.
Add a stop button to the other while loop and add an event for the stop button to stop both loops. For a simple example, see my VI posted here:
http://forums.ni.com/ni/board/message?board.id=170&message.id=176367&jump=true
Simply add more event cases as needed.
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Similar Messages
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Event Structure in Timed Loop in real time cannot work
I am a new user for LabVIEW. And I met a problem which really frastre me!!! Hope someone can help me out. Thanks in advance!
I simply want to use event structure under timed loop, which is extrmely important in my design.
However, this works very good in my computer (without connect to FPGA).
Once I connect it to FPGA, then I can run it still but there is no response!
My file is attached. Please somebody helps me!
Looking forward to your answers!
Solved!
Go to Solution.
Attachments:
Test for Timed Loop.vi 9 KBThe FPGA runs headless. Event structures are not going to work. What you need to do is have an application on your host where the user presses a button, changes a value, etc. That event should send a message via TCP/IP to the code running in the real time environment. Then the real time environment should set a control on the FPGA to the value you want.
In general, real time programming with FPGA has multiple layers.
1) Host code-> handles user interactions and communicates them to real time code via TCP,UDP, etc. Displays data to user sent from the RT controller.
2) Real time code->runs headlessly. Handles messages from Host code, processes FPGA data, communicates with FPGA much like the host code communicates with the real time code
3) FPGA -> does acquistion and passes it via FIFO to the RT
The first thing you need to do is understand the architecture and how all these pieces of the puzzle work together before throwing things down on a diagram.
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I've attached a sample VI that I just cannot figure out how to get working the way that I want. I've labeled the some sections with black-on-yellow text boxes for clarity during the description that follows in the next few sentences. Here's what I want:
1) overall -- i'm intend for this to be a subVI that will do data acquisition and write the data to a file. I want it to use a producer/consumer approach. The producer construct is the 'parallel for loop' that runs an exact number of times depending on user input (which will come from the mainVI that is not included). For now I've wired a 1-D array w/ 2 elements as a test case. During the producer loop, the data is acquired and put into a queue to be delt with in the consumer loop (for now, i just add a random number to the queue).
2) the consumer construct is the 'parallel while loop'. It will dequeue elements and write them to a file. I want this to keep running continuously and parallel until two conditions are met.
i. the for loop has finished execution
ii. the queue is empty.
when the conditions are met, the while loop will exit, close the queue, and the subVI will finish. (and return stuff to mainVI that i can deal with on my own)
Here's the problems.
1) in the "parallel for loop" I have a flat sequence structure.. I haven't had time to incorporate some data dependency into these two sequential sections, but basically, I just care that the "inner while loop" condition is met before the data is collected and queued. I think I can do this on my own, but if you have suggestions, I'm interested.
2) I can easily get the outer for and while loops to run sequentially, but I want them to run in parallel. My reasoning for this is that that I anticipate the two tasks taking very different amounts of time. .. basically, I want the while loop to just keep polling the queue to get everything out of it (or I suppose I could somehow use notifiers - suggestions welcome)... the thing is, this loop will probably run faster than the for loop, so just checking to see that the queue is empty will not work... I need to meet the additional condition that nothing else will be placed in the queue - and this condition is met when the for loop is complete. basically, I just can't figure out how to do this.
3) for now, I've placed a simple stop button in the 'parallel while loop', but I must be missing something fundamental here, because the stop button is totally unresponsive. i.e. - when I press it, it stays depressed, and nothing happens.
suggestions are totally welcome!
thanks,
-Z
Attachments:
daq01v1.vi 59 KBI'd actually like to add a little more, since I thought about it a bit and I'm still not quite certain I understand the sequence of events...
altenbach wrote:
zskillz wrote:
So i read a bit more about the 'dequeue element' function, and as I understand it, since there is no timeout wired to the dequeue element function, it will wait forever, thus the race condition I suggested above can never happen!
Yes, you got it!
As I've thought about it a bit more, there's a few things that surprise me... first, the reason the 'dequeue element while loop' errors is not because there's nothing in the queue, it's becaues the queue has been released and it's trying to access that released queue... However the problem I have is this --- Even though there's no timeout wired to the dequeue element, I still would think that the while loop that contains it would continue to run at whatever pace it wanted -- and as i said before.. most of the time, it would find that there is nothing to dequeue, but once in a while, something is there. however, it seems that this loop only runs when something has been enqueued. the reason I say this is illustrated in the next code sample MODv2 that's attached below. I've added a stop button to the "queue size while loop" so the program runs until that is pressed. I've also added a simple conditional in the "dequeue while loop" that generates a random number if it a button is pressed... but this button is totally non-responsive... which means to me that the "dequeue while loop" isn't actually continuously running, but only when an element is added to the queue. this still seems almost like the 'dequeue while loop" waits for a notifier from the queue telling it to run. can you explain this to me? because it is different from what I expect to be happening.
rasputin wrote:
I tried to open your VIs but it doesn't work. LV
is launched, the dialog box (new, open, configure...) opens and then...
nothing. Not even an error message. I guess it isn't a problem of LV
version or a dialog box would appear saying this. Could you, please,
send a image of the code?
Thanks,
Hi Rasputin, I'm using LV8. I assume that was your problem, but who knows. I've attached a pic of of altenbach's solution since it's what I needed.
thanks
-Z
Message Edited by zskillz on 10-20-2006 11:49 AM
Attachments:
daq01v1MODv2.vi 63 KB
daq01v1MODpic.JPG 116 KB -
How to run the two events at the same time by using event structure
In my project, I have to run two stepper motor which can run both forward and reverse direction by changing the control in front panel so I am using event structure. In front panel I gave two separate controls for both stepper motor such as forward,reverse and stop. I would like to do motor1 will rotate alone, motor2 will rotate alone and both motor will rotate at the same time when user click the control in front panel. My doubt is how to run a motor2 while motor1 is running at the same time please tell me the suggestion for this problem
Attachments:
motor.png 192 KBHow do you control your motors?
Most motion control systems do supply two modes:
a) position based motion: The motion axis has a positioning system (most often some kind of encoder system) which enables the motion control to know where the axis is currently located. Passing the target location to the controller will result in the axis to move to that location. This is, for most applications, the recommended approach. It does require some sort of motion controller device.
b) direction based motion: This essentially tells the periphery device for the motor to move at a certain speed into a certain direction. As it does not stop at a dedicated location, it induces great risks for many applications if there are no kill- and/or end-switches. Depending on the setup, this can be either done with motion controllers or pure by software control (e.g. "controlling" the voltage level for the motor).
If you go for a), there is not much preventing parallelism as you request.
Option b) depends on the setup. If you have a control loop in the software itself, you have to move to an architecture like the producer/consumer. Please note that this does not incorporate any security measures for the external devices.
hope this helps,
Norbert
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Can I use Event structures in a subVI?
Hi,
I have a subVI (ProvaEv1.vi) that use an event structure inside. But when I use it in a VI (ProvaVI.vi) the event structure in the subVI doesn't catch the events.
I tried to insert the event structure in a while loop but it doesn't work too.
Could you help me?
Thanks Ius
Attachments:
ProvaVI.vi 11 KB
ProvaEv1.vi 15 KB"iusn" <[email protected]> wrote in message news:[email protected]...
Thanks to all for your answers!
Wiebe! I tried to do as you suggested but I am not able to link the Event Reference Number inside te SubVI with the Event Register Number of the Register for Event in Main VI. There is e class conflict. Another question: how the SubVI can know the structure of the Register event outside?My aim was to create a modular structure but it seems very difficult, wath do you think about these problems?
The broken wire is related to your question. The event structure inside the sub vi knows about the events you register in the main, because the reference wire/control has a "strong" type. It contains information about the registered events. That is also why the wire is broken. You have to register all events, then create an indicator/control of the output. Use that control in the subvi. You have to do this every time the events change (you might use a type def if you use the control a lot).
Usually, the events that you would want to put inside subvi's are those related to user interface objects. I've had this a lot. You make a nice interface, but it's not reuseable, because the events are mixed with all the other events. Only solotion is to manually add the needed event cases in your program, and copy the code.
Even if you can put the events in a sub vi, I'd expect hanging vi's when more subvi's are registered for the same event. It's hard to tell without trying. So it's not a real solution either.
Like Chrisger suggested, the event callback might help a little, but they are tricky, and actually ment for this (they are intended for activex callbacks).
Perhaps you should look at XControls (if you use 8.2). It would be more work to replace your code to XControls, but once you're done, you have reusable code.. Haven't worked with them jet, but they are invented for this problem...
Regards,
Wiebe.
I have already create my application using event structure just in Main VI but it seems very complicate to read and keep update, I would have wanted to give modularity to my application.
Thanks Ius
SubVIEventMain.vi:
http://forums.ni.com/attachments/ni/170/203225/1/SubVIEventMain.vi
SubVIEvent.vi:
http://forums.ni.com/attachments/ni/170/203225/2/SubVIEvent.vi -
How to control the tab control using event structure?
Hi,
I am using tab control and event structure in the program.
When i run the application event is not happening for the active page.
When user switches from active page to the other page then event is taking place for all pages
So, how to get the event trigger for the active page when the application is started
For more clarification i am attaching the code "Test Control Tab using Event Structure.vi"
Attachments:
Test Control Tab using Event Structure.vi 52 KBYou have a basic misunderstanding of dataflow. Maybe you should start with some tutorials or study some of the examples that ship with LabVIEW.
The event structure belongs inside the while loop, and not vice versa. RIght now, the event structure only runs exactly once and never again.
If the stop is pressed first, the VI will stop. Game over.
If the tab control is changed (from any state to any other state!), the inner loop will spin forever as fast as the CPU allows, either executing one or the other case. It just reads the tab terminal to decide which case to execute. Changing tab never triggers any events. The VI is trapped inside the event until stop is pressed to stop the VI.
you were closer to a reasonable program in the other thread:
http://forums.ni.com/ni/board/message?board.id=170&view=by_date_ascending&message.id=287905
Have you tried execution highlighting? Maybe things would become more clear of you do.
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Problems using event structure to write new parameter values to VISA
Attachments:
FMA_event_2.vi 28 KB
FMA_event_2.vi 28 KBIt seems I'm also having trouble using forums..not sure what happened...updated and corrected thread: http://forums.ni.com/t5/LabVIEW/Problems-using-event-structure-to-write-new-parameter-values-to/td-p...
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How to use event structure of event data nodes event filter nodes in programming
hi,
I need manual of how to use 'event structure' events of 'event data nodes' and 'event data filters'...please help me....
Regards
RavindranathI'm not really sure what you are looking for here. Did you do a search in the LabVIEW help for Event Structure?
The Event Data Node just returns information about the event, like control data, control reference, what caused the event, etc.
The Event Data Filters are just used in Filter Events. This allows you to discard an event or change the data that the event will recieve.
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How can I transfer data between two while loops in parallel
Hello,
I have two while loops in parallel and I want to transfer data from the first to the second loop. The problem isthat data are transfered only when the first loop ends. I tried with queue but it doesn't work. How can I do, preferentially without global variable ?
Thanks.I join a very simplified VI's because the real works with PXI, RT, ...
When you run the "secondVI.vi", no data comes in array from the "firstVI.vi".
As I said in my first message, I tried with queue too but it doesn't work, because when the terminal go out from the while loop, while loop have to be ended to send data.
Attachments:
transfer_data.zip 20 KB -
Stop graph using event structure
How could I stop the wavform chart during running the loop using event structure?
duplicate post
Best regards,
GerdW
CLAD, using 2009SP1 + LV2011SP1 + LV2014SP1 on WinXP+Win7+cRIO
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Exit from the application using event structures
Hi
In my project i used event structure it working fine.
Now i want to exit(close) the application when i press EXIT button on the front panel.
Here i attached my project give an idea.
Regards
hari
Solved!
Go to Solution.
Attachments:
Sledge.zip 40 KBHi SAM
U saw my ok.i have one more problem when i run the program(main vi) all the remain sub vi's also opened.
i want open sub vi when i press a button on front panel.
i have made small changes to it.
Regards
hari
Attachments:
Sledge.zip 41 KB -
Event Structures and Do /While Loops
I have an Event Structure inside a Do/While Loop. One of the buttons in the event is STOP which stops the do while. The Stop Button itself is inside the event as suggested in the help. My problem is when I hit the stop button everything inside the Do/While runs 1 more time. Other than than the code works perfectly. is this normal behavior for a Do/While ..Event Structure??
The attached file is the code in a nutshell. I know it can sometimes be diffcult to TS w/o the actual code. Prob is I wrote it in LV2011 on the Lab PC and I have LV2010 at my desk. I don't have internet access in the Lab..of course.
If I hit the OK button 2x's it "does something...does something...build array" then again a second time. The build array is added to with each click of a button in the event structure. If the user hits the STOP it dumps the 2x's worth of data out to excel..except I get 3 rows of data rather than 2...as if the inner loop ran one more time.
Anyways. the only thing that caught my eye is the fact that I don't have a sequence structure around the "build data here" portion of the code. Would that affect how the STOP inside the do while loop is handled??
Attachments:
event_Do_While.JPG 90 KB -
Calling a VI in a subpanel with parameters inside an event structure and using an abort button
Hi all,
I have a control panel with a tab control and two tabs have a sub panel in them. At runtime I load the VIs I want in to the sub panels. In the control panel event structure I want to start each of the VIs and monitor the execution state so I can abort the VI while it is running. One method I use can run the VI and the abort event will work (see example). The second method I use does not and this is what I want to do! I have many inputs to the VI I want to pass so placing the VI in the event blocks everything else and it has to wait until the VI has completed, so I cannot monitor the execution state.
I have attached an example of what I want to do.
Any help appreciated.
Martin
Solved!
Go to Solution.
Attachments:
SubPanel.lvlib 2 KBHello,
You can do this with queues.
The main vi and subpanel vi's should be based on the producer/consumer (events) and you handle the front panel events accordingly in the respective vi's.
Name the queues in obtain queue , for example the Main being MainQ, subpanels SubPanel1Q, SubPanel2Q. When you start the application, initialise the main vi and also run both of the subpanels (just to make sure that the queues are first obtained by themselves). Then you can use obtain queues to do inter vi communication.
For example if you need to send data from main to subpanel1, use obtain queue and use the name SubPanel1Q, pass the required data & command and voila. Subpanel1 vi will receive your message. You can do this anyway you want. Hope this helps.
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Event structure in "for loop" and stacked sequence
I tried to put an event structure into a for loop sequence, then used a pause button to pause the program (one loop with event structure.vi). The pause button functioned normally since the program could be paused whenever the button was pressed. Then, I put this for loop sequence into a stacked sequence (Problem.vi), which has 2 frames and every frame has the for loop sequence in it. After the pause button was pressed once, the pause button and stop button will no longer effective anymore. Where should I modify so that this program will work properly? Thanks a lot.
Attachments:
Problem.vi 42 KB
one_loop_with_event_structure.vi 27 KBAh, at last something weird !
The answer is simple : don't do that !
You should either avoid having 2 event structures handling the same events, or learn how to process dynamic events.
Why didn't you read the answers to a question posted a few hours ago (still on the overview page of this forum ?). See here.
Chilly Charly (aka CC)
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