How to pause and stop two "for loops" in an event

Hi
The main menu runs first and then goes to reading menu. After "Start Reading" button is pressed, the reading process will take readings.
1) During reading process, if the "Pause Reading" button is pressed, I want that the two "for loops" are stopped and the two "for loop" counters do not reset. After the "Start Reading" button is pressed, the two "for loops" will continue to run.
2) During reading process, if the "Stop Reading" button is pressed, I want that the two "for loops" are stopped and the two "for loop" counters are reset. After the "Start Reading" button is pressed, the two "for loops" will run again.
The attached two VIs are simplified my real application. Any help will be appreciated.
Thanks
Steve
Attachments:
Main Menu Test.vi ‏9 KB
Reading Menu Test.vi ‏23 KB

You can't have those loops inside of the event structure. Currently, when you press the start button, the reading has to finish before the event case finishes. This will prevent the stop can cancel buttons from being processed by the event structure.
You need another loop that can recieve commands from the event loop. Look up the Queued Message Handler. That should get you a good start on the command process.
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How can I start and stop two parallel loops?

Hello,
I want to control two parallel loops with different timing in a vi . That means to start loop 1, then loop 2, stop loop 1 or 2 restart loop 1 ...
But if loop 1 is running I cannot start loop two and reverse.
Can someone help me and show whats wrong in my example?
Thanks,
Christian
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Attachments:
Parallel loops Test.vi ‏46 KB

Hello Christian,
The reason why you can't do what you want is in fact quite simple.
You have an external loop that is "over" the two inner loops.
So when you stop one of the inner loops, the outer loop will still be in the same iteration until the other inner loop ends - stop the other inner loop.
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Attachments:
Parallel loops Test2.vi ‏48 KB

How to pause and restart a timed loop in Labview

I am trying to pause and then restart a timed process (series of stepd that happen at precise times), which is implemented using a timed loop.
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Roxanne,
Well, it's not exactly a "pause", but here's a way to stop and re-start your Timed Loop.
See the attached example in LV2010.
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Attachments:
timed loop.vi ‏39 KB

How to stop and start a for loop

I've got code and a for loop running in a while loop. What I need to do is simply pause the operation of the for loop until an requirement is met, and but maintain its iteration position throughout each pause interval (not necessarily timed, just paused until the next requirement is met). I've tried wiring a boolean to the "continue if true" terminal of the for loop, but the iteration count restarts to 0 when the loop is started again. Is there a way to stop the for loop, and continue at the particular iteration it is at?
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Breakpoints, whether normal or conditional, are just meant for debugging of your code. I had the sense from your question that the pausing you want to do is a part of normal operation of your code. I would NOT recommend using a breakpoint for that situation. It would bring up the block diagram showing the breakpoint when it occurs. A user besides the programmer would not know what to do in that case.
Yes, both the inner and outer loops would have shift registers.
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How to make a button to stop and run a for loop?

How to make a button to stop and run a for loop? and if it is stopped it shall start from where i t stopped.

Your VI has some very fundamental flaws.
The start/stop button is outside the FOR loop, thus it will NOT get read during execution of the FOR loop, but only before the FOR loop starts. Think dataflow!
Thus the terminal of the start/stop button belongs inside the FOR loop.
Your FOR loop iterates 20x, which probably takes about a nanosecond. You will NOT be fast enough to reliably press the start/stop button during a specific iteration of the FOR loop.
Your code does not "stop and run" a FOR loop (sic). The loop always spins, but executes an empty case when "Stopped". I guess that's what you actually want?
Once you solve (2), the x indicator will contain a random value whenever you "stop".
As soon as the 20 iterations complete, the outer while loop spin an things start over, another nanosecond later.
Place e.g. a 500ms wait inside the FOR loop to solve this.
Don't place terminals of indicators on top of formula nodes.
Your formula does not produce any output, so really has no purpose.
Use a real "stop" button to terminate the while loop (mechanical action: latch when released). Right now you are using a plain switch, which does not reset to false before the next run. This means that you need to manually reset it before running the program again.
It is oftern useful to operate the VI in execution highlighting mode. You will immediately see that your button does not get read during execution of the FOR loop. Try it!
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How to stop a "for" loop

Hello,
Do you know how I can stop a for loop ? because when I click on the stop switch on my front panel, the VI don't stop and continue to run the loop.
Peter.
Labview 2010
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Peter,
It sounds like you need a while loop, not a for loop. A button or switch does not traditionally control iterations of execution for a for loop.
Please post your code so we may help better.
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Actually if the server throws exceptions when it stops (which it always has since we applied patch 10.1.3.3) this technique will pause until a user responds to pop-up ... So a better way (I think) is -
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Code golf: stop two while loops with guaranteed iteration ratio

Proposal
In the vein of the Perl tradition, I'd like to see if there's any interest in solving short programming puzzles in LabVIEW. Anyone can post a problem and define the rules for solving it.
Here's a beginning/intermediate question to whet your "palette".
Description
With one user-action, how would you stop two while loops such that the ratio of their iterations is the always the same? One concrete way to visualize this situation is in taking measurements: two instruments use the same timing source to take measurements, but second divides the clock down so that it is an integer factor slower than the first. For example, if the slower instrument is four times slower, then at the end of the VI, if the slower instrument takes 100 measurements, the faster instrument has taken 400.
Rules
You may only use vi.lib
You cannot include any other subVIs
Your solution must pass for loop1 interval as low as 25 ms
Template (attached in LabVIEW 2009)
If folks are interested in this, then let's figure out how to make future problems better. Please post your suggestions and critiques, but only if you also post a submission ;-)
Solved!
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Attachments:
Multirate Loop Code Golf.vi ‏11 KB

Norbert_B wrote:
a) You work with an integer factor of speed. While this matches many application areas, there are still cases where the factor has to be floating point (e.g. 2.5). Additionally, the factor might "invert", so the master loop runs slower than the slave (factor 0.5 for instance).
It sounds like you're about to post another code golf question. If you think the problem scope is too small, you're welcome to fashion one to your taste. Thanks for volunteering :-D
Norbert_B wrote:
b) This example does not take into account that the hardware has to be synchronized with more accuracy than the software supplies (PXI?). If hardware synchronization is required, there are two possible ways:
- The factor can be included in the synchronization (using PLL for instance)
- The factor has to be software implemented by data reduction for the task running at the lower pace.
Hrm, maybe puzzles aren't really your thing after all. You are correct: I did not define every constraint that can lead to a provable best closed-form solution, but that does not prevent people from stating their assumptions and forming creative, well-reasoned, and still correct designs. I overlooked this reading of the description and neglected to add a statement that said solvers were free to add their own conditions. I will do so in the fugure :-)
If we choose the first of your suggestions, the VI must still retrieve the data at different rates. You can dedicate a loop for each instrument to decouple any jitter and latency introduced by their connectivity or internal operation; this adds some margin of safety when there is thread and driver contention. You can also implement a single counting loop like altenbach and forego the multiloop complexity.
Norbert_B wrote:
c) You don't state anything about "what happens with the data". Is this time consuming? Does it introduce additional delay in loop iterations? Is it OK to have data loss?
I don't know -- you decide, you disclose, and you solve :-)
In my specific situation, the measurements are time consuming and do add delay (each data "sample" is 5-20 megabytes), none can be lost, and the data must be available for others to analyze later. In addition, the amount of data is saturating the hard disk throughput. If a particular write takes too long, the instrument driver may overwrite a yet unfetched sample, which is unacceptable. I did not add these details to the problem discripton becuase they don't impact the puzzle.
I don't want to burden people with my situation and ask them to solve my problem: I want to encourage them to bring their intuition and experience to a discussion. This is the design process at its heart: understanding why and how constraints affect your decisions. If a person states the additional conditions they've assumed, readers can learn why, and more importantly, when a Notifier might be more desirable than an Occurance or a Queue more robust than a Data Value Reference.
The best NI-published advice for stopping multiple while loops (https://www.google.com/search?q=labview+stop+multiple+while+loops) is laughable (and is the "solution" in my template).
Would you care to re-approach and contribute to this puzzle? I suspect you have a lot to offer :-)

Stopping a For Loop, part 2

Hello. Thank you everyone for your help, getting to this point. I asked for help to create a stop condition, while a For Loop is running. I was given many ideas and selected the one that used local variables. It works well however, if I am in the "Test in progress" state, in the first For Loop, and the "Stop" button is selected from the front panel, when it stops the Vi, it sends the value "5" to the second For Loop before going to the "End" state, which puts it to "0", then stops the Vi. What this Vi is doing is feeding 0-200VDC signal to an eddy current sensor, then it feeds 200-0VDC going the other direction. I have tried sequencing, putting in timers and a few other goofy things but I can not get the Vi to stop in the first For Loop, without the Vi performing the initial "5" to the second For Loop. Someone had mentioned using an event handler, in my previous post. I practiced for quite some time, trying to understand how to use an event handler but am not much the wiser. Any and all input would be greatly appreciated.

altenbach wrote:
ceilingwalker wrote:
You are autoindexing way too many thing between the two FOR loops I was doing this to create a data dependency, at least that was my thought process behind it. As far as the physical channels and VISA refnums, I did it this way so I didn't create more controls for the front panel. Being my first project, I am very certain my logic is flawed, this is why I like posting here and getting feedback from
You have many visa sessions that (hopefully) never change during the execution of the loops, so why woold you turn them into an array of 11 identical elements just to autoidex them out again at the next loop. Change the tunnels to no autoindexing and things would look cleaner. Why are these session controls inside the loop? Are you expect them to be changeable during loop execution or would that screw up the results?
Wounld't it be easier to simply create an up&down ramp once and use a single FOR loop, autoindexing on the ramp? You have way too much duplicate code!!!
If you don't want the second loop to run when the first one is ended prematurely with the stop button, put it in a case structure I tried a Case structure for the second For Loop. I couldn't find a way to change conditions that didn't affect the Vi's overall performance.
Then show us what you tried! That should be trivial to implement. Why would a case structure affect performance? Makes no sense!
Why would a case structure affect performance? Makes no sense! I used a boolean operator to change the state. When I used a false, it worked for that problem but shut down my Vi before the second For Loop.
Wounld't it be easier to simply create an up&down ramp once and use a single FOR loop, autoindexing on the ramp? You have way too much duplicate code!!! I tried using one For Loop to begin with but because I had to ramp up, then ramp down, I couldn't figure out how to use just one. I needed an Add function for the ramp up and a Subtract function for the ramp down.
Why are these session controls inside the loop? Are you expect them to be changeable during loop execution or would that screw up the results? No Sir, the values are not changed during operation. I did this because I wanted it to display the data on the front panel, during operation of the Vi. For display only.

Pause and Stop implementation in streaming audio

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I am building a program that transmits audio over a TCP connection(using ServerSocket and Socket classes). My problem is that I am not being able to correctly implement the 'Pause' and 'Stop' option. Let's go into more details:
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thank you for your reply captfoss, i see that you're always the first one to reply, i am really grateful for that.
yes, i have already written code for issuing the stop and pause command, but i don't know how exactly one should implement them. i mean, i sure there'll have to to be some sort of lock object on which notify( ) and wait( ) methods will have to called, but i am not being able to do that. . something similar (but not same) thing has been discussed here http://www.javalobby.org/java/forums/t18465.html at the end of the page, please help as i have tried everything i can and still it adamantly refuses to work..

Synchronisation of two for loops...

hii....
i am using two for loops and i want that each iteration for both for loops start at same time..
actually i want synchronisation between these two loops..
so when the each iteration of both loops will start at same time then these will be synchronised..
also if one loop take more time in one iteration then the other loop should pause until the other's iteration completes..
please hlp me...thanks...
thanks
do not hesitate to give kudos
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Go to Solution.

hiii
you are right thatthe loops will be synhronised as Labview executes code via data flow.
here i mean of synchronisation is that i want each iteration to be started at same time only...
this is what i am not getting..
i have tried it to b done by defining a local variable in one loop and using its value in the other but it did not work..
i hav tried some more methods but in vain...
so i am here...
thanks..
thanks
do not hesitate to give kudos

Visa open and close with "for loops"

Hello everyone
In my program I used two "for loops" which include visa write and read for a RS32 port. it is not possible to close a devise with visa close as the out put is changed to 2D array!!! would you please help me with this error
Attachments:
ACU_232.png ‏108 KB

sam009 wrote:
Thanks for reply,
It works for "for loop" but what about "event structure loop" still is error for that.
Right-click on the output tunnel and uncheck "Use Default if Unwired". You will now be forced to wire the VISA Resource through each case.
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How to pause and stop two "for loops" in an event

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