Problems closing several loops in a state machine with an event structure

I am having some problems closing three loops running in parallel in a state machine. I have one loop for an event structure to monitor user controls to change the state. The other loop is the state machine which will control an actuator, and the third loop is for data aquisition/analysis. I want to be able to hit the stop button and go to a "shutdown" state where I can home the actuator then close the loops and finally go to the last "shutdown" subdiagriam in the flat sequence structure. Currently when hitting the stop button it goes into the shutdown state and will end the state machine loop but it appears the other loops are not closing until I hit the stop button again. Could this be due to using a local variable for the boolean to control the loop conditions? I attached a screenshot of the block diagram. Any advice would be great!
Attachments:
example.png ‏108 KB

You have a classic race condition due to overuse of local variables. If the stop event fires in the upper loop, the local variable connected to the loop termination condition has already been read (it is false!). This means that the upper loop will iterate once more and again wait at the event structure for the next event. At this time, the local variable connected to the loop termination is TRUE, but the loop cannot complete until the event fires again, for example if you press the stop button once more.
The correct way is to connect the terminal of the stop button across the right event frame directly to the loop termination terminal. Now it will get the TRUE value correctly once the stop event fires for the first time.
LabVIEW does not execute left to right, execution order is determined by the wiring.
I also agree with the above message that you should rethink and re-architect your code using established coding guidelines.
LabVIEW Champion . Do more with less code and in less time .

Similar Messages

State machine with using event case

Hallo everyone,
i have a question about how to realize the "Timeout". In the flow diagram below we can see 2 different situation:
1. in the 1st Situation i have used the state machine, it begins at state 1, which contains a event case. In there it will be at first determined, if the input value has changed within 10 second, if it didn't, the state machine will go to state 2, if it 's changed, will be furthermore determined, whether the input value equal to 3, if yes, the state mashine will jump to state 3, if no, jump back to state 1. (this VI i have done before, you can take a look at the Attachment).
2. my question is in the 2nd situation. It begins also at state 1. In there the input value can also be changed (once or many times) or not. If the value has not been changed within 10 s, or even though it's been changed many times within 10s, but it's never been equal to 3, the state machine will go to state 2; only when the input value within 10s equal to 3, it can jump to state 3.
This problem i have no idea how to solve, does anybody have idea or better methods?
thanks a lot!!
Solved!
Go to Solution.
Attachments:
situation 1.vi ‏12 KB

The statement in the OP is not covering all cases.
mexaviesta wrote:
2. my question is in the 2nd situation. It begins also at state 1. In there the input value can also be changed (once or many times) or not. If the value has not been changed within 10 s, or even though it's been changed many times within 10s, but it's never been equal to 3, the state machine will go to state 2; only when the input value within 10s equal to 3, it can jump to state 3.
This problem i have no idea how to solve, does anybody have idea or better methods?
thanks a lot!!
Just check my implementation for Situation 2 and let us know, if it works for you.
I am not allergic to Kudos, in fact I love Kudos.
Make your LabVIEW experience more CONVENIENT.
Attachments:
Situation 2.llb ‏40 KB

Need help created state machine with timed digital output

Hello everyone I'm new in LabView especially about how to make a state machine. I want to make simulation about state machine with digital output. In Front Panel there are volt_in as an input slider (0-10 V), two numeric control (upper limit and bottom limit), a waveform chart to plot those 3 value, and three boolean (P0.0, P0.1, P0.2) as an indicator. Boolean indicator will on if input from slider exceed the limit in certain situation. This simulation will work as follow:
1. Define the upper & bottom limit (ex. 8 & 4V)
2. Make an input from slider (0-10V)
3. If input (2) exceed the upper limit but less than 10 second (ex. you have 9V input for 8 second, but after 8 second you change the slider back to normal between 4-8V) then the boolean indicator P0.0 & P0.2 will stay off
4. If input (2) exceed the upper limit more than 10 second (ex. you have 9V input for 4 second, change to 8.5 V for 3 second, and then change to 10V for 3 second) then the boolean indicator P0.0 will turn on for 5 second, turn off, then follow by indicator P0.2 for 5 second, and turn off
5. Wait 15 second, then repeat process from (2)
Same process for input that exceed the bottom limit (P0.1 and P0.2 as indicator).
Can you help me make the block diagram of this process? I will appreciate any of your help.
Best Regards
juventom
Attachments:
State Machine Digital Output.vi ‏28 KB

I would highly recommend you to open the template in LabVIEW to design state machines. You can the Standard State Machine template if you go to File -> New.. and Browse to VI -> From Template -> Frameworks -> Design Patterns.
Also, here is a good explanation of one:
https://decibel.ni.com/content/groups/northeast-oh-labview-users/blog/2009/09/08/state-machines
Adnan Zafar
Certified LabVIEW Architect
Coleman Technologies

An example of a state machine with transition array?

I am looking at state machine design patterns and am interested particularly in a state machine with boolean trasition array which defines the next state to be executed using an array. Here, the index of the first “True” boolean in the boolean array corresponds to the index of the new state in the array of enums. Has anyone got an example of this design pattern as it would greatly help in my understanding of it. Refer to figure 3c in http://zone.ni.com/devzone/cda/tut/p/id/3024#toc2 for clarity on what i am asking for.
Thanks in advance.

That seems like a lot of extra work. Why not just use a queue, and queue up the enum you want to go to next? Look up examples on queued state machine. No need for an array and then a boolean to index that array. here is an example
CLA, LabVIEW Versions 2010-2013

Shutting down a queued event state machine with multiple parallel loops

I am trying to find the best way to shutdown a program that consists of a queued event state machine architecture with multiple parallel loops. Can anyone recommend the best way to accomplish this in my attached VI? (From browsing the forum, this seems to be a common question but I haven't found a solution that works for me.)
I welcome any other feedback on my code as well, if anyone is willing to offer it.
My Program Requirements:
If the user presses the "Shutdown" button, the program should prompt the user with "Are you sure you want to stop the program?" and then either return to the Idle state or proceed to stop the program. Additionally if there is an error, the program should prompt the user with "Clear error and continue, or Stop program?" Then either return to the Idle State or proceed to stop the program.
Details of architecture:
The program consists of 3 parallel loops: (1) an Event Handling loop that enqueues various States to a State Queue, (2) a State Machine which enters the latest state that is dequeued from the State Queue, and (3) an Error/Shutdown handling loop which processes any errors in the Error queue.
During normal Shutdown, in the Event Handling loop the "Program.Shutdown" event case executes, and the States "Shutdown" and "Idle" are added to the State Queue. In the State Machine, the "Shutdown" state is invoked. A special error code "5000" is added to the Error Queue. In the Error/Shutdown handling loop, the "5000" error triggers a prompt that asks the user if they want to stop the program. If the user chooses not to stop, a notifier StopNotif is sent to the "Shutdown" state and "Program.Shutdown" event case with the notification "Go". If the user chooses to stop, the notifier sends the notification "Stop". The Event handling loop and State Machine are terminated if they receive the notification "Stop".
In case of error, the program behaves similarly: if the user chooses to clear the error and continue, the program returns to the "Idle" state.
HOWEVER - if the user chooses to stop the program, the program stalls. The notifier that is sent to stop the Event Handling Loop and State Machine cannot be read because the Program.Shutdown event case and the Shutdown state (which contain the "Wait for Notifier" function) are not active.
I have been able to activate the Shutdown state by enqueuing it in the Error/Shutdown handling loop. But I don't know how to activate the "Program.Shutdown" event programmatically, and thereby access the "Wait for Notifier" function inside it.
I tried to place the "Wait for Notifier" function outside the event structure, but then the Event Handling loop never completes. Placing timeouts on the "Wait for Notifier" and on the Event structure makes the program work, but I want to avoid using timeouts because I don't want to turn my event-driven program into a polling-based program. I'd also like to avoid using variables or property nodes to stop the loops, because that requires creating a control/indicator for something that the user doesnt need to interact with.
Thank you!
Solved!
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Attachments:
Queued event state machine parallel loops empty.vi ‏46 KB

Thanks for clarifying that, Ravens Fan.
I marked crossrulz as the solution for pointing out User Events to me.
I also adopted Ravens Fan's suggestion to keep the Shutdown procedure out of the Error Handling Loop. This has simplified the architecture by eliminating the need for Notifiers. Instead, I have used booleans in case structures to stop the Event Loop and State Machine, and Release Queue to stop the Error Handling Loop.
For reference, I'm attaching my corrected code.
Thank you to everyone who helped!
Attachments:
Queued event state machine parallel loops empty in progress.vi ‏44 KB

Performance of state machine with enum vs string?

I am laying out the groundwork for a very large state machine. It will have about 60 to 100 states. I kind of want to use an enum for selecting the states for convenience. But then if I use a string I can use Jim Carmody's case select tool so that wins out in convenience in one respect.
One concern about using a string is performance. Since an enum is just an integer wouldn't the selections perform better? I need to squeeze out every ounce of performance and in fact this state machine will be set for subroutine priority. Another concern that I have about a typedef enum is that I have heard something about the possibility of them getting "out of sync" between VIs when you edit them. Is there some way to avoid that, such as making sure all VIs that use this typedef are in memory when editing it?
=====================
LabVIEW 2012

Steve Chandler wrote:
As for the number of states, I am pretty sure that it has to be one state machine. I'm afraid I cannot give a lot of details.
I am having trouble figuring out the "has to" part.
See this thread for designs I have posted previously.
In this SM
please look the section that is entered from "Change Request 8 " can take multiple paths but all ends at "Stop Monitoring? 15". I could have implemented that as a sub-SM and it would have reduced the number of state required for that part of the work from five to one.
Any time I see "single entry, fan out, merge" I think sub-SM.
This could also help with your shift register as well because (again seea bove) the bulk of the ose states deal with Logging so rather than use a SR, put what would have been in the SR (file path or ref) to be used there OR possibly an AE that can be used in each of those states.
So I still don't understand why sub-SM aren't a possiblity.
Trying to help,
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

Queues even driven state machine

Hello,
i am working on this software and doing it via queues even driven state machine but Im having problem with. I understand how queues and event structure work but here's my problem. when I pass a massage to my state machine from the event structure via Queues. It works fine then stop. My goal is for the second loop where the state machine is to continue working but not wait on the next message. I tried ot use a time out on the queue but that didnt work. Is there anyway i can do that. I attached the VI. it's not finished yet but you will see what Im doing with it
Attachments:
check.vi ‏38 KB

Bob, thanks for your input. I attached the full vi for you to have a better understanding of what Im talking about. Keep in mind though it works it isnt closed to finished.
My goal is to toggle different boolean that will generating different data. Each Boolean will generate a messgae via event structure to my message handling loop. once the message is passed, that loop will queue in the state of the data to generate. Once dequeued my plotting loop will generate the data then queue it in for display. It seems like there are too many queues being used but that is how I plan to write the VI. I want my 3rd loop to always generate the data so that my fourth one can display but that isnt working for me since the 3rd loop is always waiting on a message from teh 2nd loop ( messge handler). If you foolow the data flow you'll see what I am referring to
Attachments:
check2.vi ‏499 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

Allow state machine while loop to end only in 1 of the states?

What is the best way to ensure that the while loop that surronds state machine case structure only ends in a certain one of the states?

I have solved the problem of having the VI not stopping (apparently it was due to an event structure). However, now I have another slight problem. I need the state machine to terminate on either of two conditions:
1) If a stop button is pressed
OR
2) if the end of the sequence is reached.
As I have implemented it so far the VI terminates because of the second condition and does not allow me to terminate it by pressing a 'Stop' boolean button. I know that this might be a bit fundamental and simple but I'm new with state machines on labview.
Thanks.
Attachments:
State machine.vi ‏21 KB

How to use elapsed time function with state machine in Lab VIEW

Hello
I've been trying to use state machine with elapsed time function in order to sequentially start and stop my code. The arrangement is to start the code for 1 minute then stop for 5 minutes. I've attached the code, the problem is when I place the elapsed time function out of the while loop it doesn't work, on the other hand when I place it inside the loop it does work but it doesn't give the true signal to move to the next state.
Could you please have a look to my code and help me to solve this issue.
Regards
Rajab
Solved!
Go to Solution.
Attachments:
daq assistance thermocouple(sate machine raj).vi ‏436 KB

Rajab84 wrote:
Thanks apok for your help
even with pressing start it keeps running on wait case
could you please explain the code for me, the use of Boolean crossing, increment , and equal functions
Best Regards
Rajab
OK..I modded the example to stop after 2 cycles. Also recommend taking the free online LabVIEW tutorials.
run vi. case statement goes to "initialize", shift registers are initialized to their constants. goto "wait"
"start"= false, stay in current state. If true, transition to "1 min" case
reset elapsed timer with True from shift register(counter starts at zero)."time has elapsed"=false, stay in current state(1 min). If true, goto "5min" case
reset elapsed timer with True from shift register of previous case(counter starts at zero)."time has elapsed"=false, stay in current state(5 min). If true, goto "1min" case. Also, bool crossing is looking for "true-false" from "5 min" compare function to add cycle count.
Once cycle count reaches 2, stop while loop....
Attachments:
Untitled%202[1].vi ‏42 KB

How do I add new data to the same file in a State Machine?

Hello,
I have a State Machine, with a State where 3 samples of data are collected in a For Loop. I would like to save this data in a file and keep adding new data to the same file each time I get to this state. The problem I'm running into is that each time I reach this State, my old data in the Excel file gets replaced with the new data instead of being continuously added in the same file.
Ive tried Shift Registers but I may not be using them correctly since my file keeps displaying only 3 new data points.
Any ideas will be appreciated!
Thank you, so much.
-Peter

Where should I place these shift registers? Where should I place my File I/O VIs? Is it possible to use the Write to Spreadsheet File VI in this situation?
Ive attached a very simple example of the problem. Thank you.
Attachments:
StandardStateMachine 2.vi ‏16 KB

How to start and stop video acquisition in a state machine

hello,
I'm a neuroscience student and here's what I'm trying to do: 1) trigger a GigE camera (200fps), 2) start video acquisition, 3) trigger a light that will stay on for x miliseconds, 4) trigger a valve that will blow an air puff, 5) stop the tone and the valve simultaneously and 5) stop the video acquisition 1second after 4). For that, my VI is a state machine, with a state for each trigger (ex, 1 state for trigger camera, 1 state for trigger light, ect) plus a state to "stop" and a state "time to wait". Everything was working except the video acquisition - the program would trigger the camera but only acquire one frame, because it wasn't running in a while loop and this is my first question: for a video acquisition is it always necessary to have a while loop?
I assumed the answer was yes, so I built a "consumer" loop for the camera. Putting a queue in the state "trigger camera" in the producer loop, I was then able to start the video acquisition but now the problem is to stop it in the right time. I have another queue in the "stop" state in the producer loop, but it isn't able to start the "stop" state in the consumer loop, I think that may be because the consumer loop gets "stuck" in the while loop.
I hope you can help me, the VI is attached. Thanks!
Solved!
Go to Solution.
Attachments:
trigger_cam.jpg ‏345 KB
trigger_stop.jpg ‏354 KB
Conditioning MS vi 2010.zip ‏68 KB

Hi Gak,
Thanks for the suggestions. I still didn't got it to work though. I moved the stop command to inside the while loop like you said but it didn't work. The problem seems to be in the communication between the producer/consumer loops. When I run the VI in highlight, the queue message "trigger camera" leaves the producer and arrives at the consumer loop in the appropriate time, starting the "trigger camera" state of the case structure. However, the message "stop" doesn't seem to be sent by the producer loop, so the consumer doesn't receive a signal to start the "stop" state of the case structure. Can you think of anything I should change in the producer loop so that the second state (stop) is added to the queue?
About the functional global, I read about it, it seems that either that or a local variable could work, but I don't quite know how to implement it in my state machine, since the stop of the first while loop isn't activated in the "stop" state but in the "shutdown" state. It works more or less like this: after 10 loops of triggering and stopping the camera, light and valve (so after acquiring 10 movies), it goes for shutdown. Can you show me what you had in mind with the functional variable?
Attachments:
Untitled.jpg ‏286 KB

Running SubVIs with state machines in parallel

Hi,
I'm new to labview, working on it for a couple of weeks.
I'm building an application where there are a number of identical elements atht each is controlled by an identical state machine which is independent from all others.
My problem is how to place each state machine in a subvi and running them in parallel.
Each of the subvi has a while loop for the state machine, and the program gets stuck inside never entering another subvi.
Is there an elegant way to run a couple of SubVIs each holding a state mchine in parallel?
I come from the VLSI world so there is no problem implementing this kind of logic in hardware description language but the labview way to do it eludes me...
thanks you very much for any help,
Eyal.

braxat2000 wrote:
Hi,
Thank you everybody for your kind help.
The problem was solved and my application is OK now.
For future reference,
I used the execution reenter subvi to allow multiple instances of it in parallel, and added a global variable that the subvis can change, and the main can read from.
Used semaphores to make sure correct parallel write to common sources.
Cheers,
Eyal.
Great solution- but how to avoid race conditions in the global variable? Globals are notorious for causing headaches, nightmares and nausea so if there is a way to avoid them and enforce a bit of cause- effect its highly desirable. In this case you have clones of a re-entrant vi running in parallel so you CAN'T use a functional global (the most common solution see Ben's famous Action Engine nugget)
Since we can't enforce data dependence we need something else as a cause-effect team..... Change event dependency would be a good substitute. Two methods for getting this type of dependence would be a dynamic event or my favorite the "Named Queue" set the data type of the named queue as a cluster of instance of source and data from your global and the main loop will be able to see EVERY write to the queue AND the source. Moreover the queues datatype can be expanded to offer any information the main vi needs to be a good executive. In fact a new sub vi that "monitors status" of the clones would make the application highly scalable and robust.
Jeff

Help me with a state machine design

I have a little bit of a problem. I have a system with several modes, each selected by the user and called with a case structure. Each case in the case structure is its own state machine with a few states (like 4-6). Now here's the catch. I need one of the states within one of the modes to call and execute an entirely different mode (and all of its states) without actually changing the mode command, and to do so every iteration until I jump out of that state into another state within the first mode.
Is there a simple way to do that that I'm just not thinking of?
Lee Jay

Lee, my first thought would be to use just a big state machine. For example if each mode needs 4 states, mode 1 gets states 0-3, mode 2 get states 4-7, and so on. This way, if you need to change modes in the middle of another mode, you just direct the state selector to the state that starts the mode. (If that makes sense). It's not real elegant, but it works fairly well as you still maintain the flexibilty of the state machine design, including the ability to add and rearrange cases.
Don't forget you can use any method to select the cases, including strings, so you have full flexibility with how you setup case select.
Troy

Using multiple events structure inside state machine to control the Tab

Hi y'all,
Anne here.I have a Tab indicator in my front panel and I want to be able to control the flow of my program based on what controls I clicked inside the tab. I am using a state machine architecture and inside every state, I use an event structure to check for user interaction to determine the next state and what tab page is going to be displayed next. This means that I am actually using multiple event structures in my application and I use them in just one while loop, but just that they are not running in parallel since I am only using "one event structure per state" which means that only one event structure is running at one time. My questions is, programming technique wise, am I doing it correctly? So far, I am not facing any problem (I am still in the early stage of the project) but I want to check with you all first on your opinion regarding this architecture. Will there be any issue on using multiple event structures in a vi? Since I will be using a tab, and the controls available in the tab will be the controls that will control my event structure for that state, by right, there should be no issue. Am I correct to assume this? Is there any limit on the use of event structures? I have attached here a simple sample of the architecture that I am talking about for your reference. I have attached a 2010 version and a 8.6 version. Let me know what you think or any opinions that you may have.
Hoping to hear from you soon! Thanks so much in advance!
Cheers!
Anne
Attachments:
State Machine-Event Structure Sample_2010.vi ‏19 KB
State Machine-Event Structure Sample_8.5.vi ‏25 KB

Hi jak888,
I decided to use tabs cause I don't want to have subvi pop ups every time i need to perform the process in the state and show an update in the front panel. This is actually going to be more of an ATE where you will have to choose first whether the one using is the operator or the engineer. If the operator is logged in, she will proceed to choose what test to run (this state will have its own event structure). This part, I don't want a pop up, so what happens is that from Login page, if the user logs in as operator, the tab will automatically switch to the Test Selection page. After selecting the test, it will proceed to Start Test state and the tab will show the Result Summary page. If the user logs in as engineer, then a totally different tab will be automatically shown next and so on. By doing this, I will be able to show an update on the front panel objects without having the subvis pop up. I will also just need to use the call reference functions to call my subvis, making my Main VI more generic. The tab Page header will be hidden so the operator will actually not see that there is a tab and that there are a lot of controls and indicators cause they are hidden in the tabs and that page will only be shown based on what they selected from the main tab.
I appreciate your thoughts! thanks so much!

Problems closing several loops in a state machine with an event structure

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