Well-oiled typical state machine

In my new-to-LV adventures I feel like I'm spinning my wheels to revinvent the wheel.
My project has modest complexity and it was advised to be a state machine architecture.
Can you post an example of a well-made state machine that of low to medium complexity?
I think If I could study several good examples, I could answer most of my questions.
Please post if you would like to share.

http://www.ni.com/tutorial/7595/en/
http://www.ni.com/white-paper/7604/en/
http://k12lab-support-pages.s3.amazonaws.com/lvadvancedhome4.html
https://www.youtube.com/watch?v=vtw6HMwaTIQ
This lot took me at least 8 seconds to find with Google. Invest a little more time and you could probably do even better
(there really is a lot of stuff out there!)
EDIT - okay so this crossed with your last post, and is probably a tad sarcastic and looks even worse following your last reply. But you will do well with a bit of searching because, like you want to not re-invent the wheel, neither does everyone else when there are already so many good examples out there.
EDIT - for a little more complexity, check out the Continuous Measurement and Logging sample project template - althogh a slightly different architecture it has all the elements you listed and more.

Similar Messages

State Machine Demo

Hi Folks,
I am a newbiew LabVIEW developer studying & working towards my CLAD certification.
I already took LabVIEW Basics I & II and I decided to make a simple state machine (please see attached VI).
I was hopping if there is anyone out there who find a way for the VI be optimized so I can see my weakness.
ThanX in ADVANCE!!!!!
Attachments:
StateSimulatorfromEE428.vi ‏71 KB

Overly complicated and convoluted is the word.
I haven't even tried to undestand what you are juggling with all these string operations, but there's gotta be a better way!
Case 4 and 5 are identical except for a diagram constant. They can be comined into one case.
"state operation" is a control, but you are constantly writing to it via local variables. This mean it cannot be reliably operated, because the set value could be reset before it is used due to race conditions.
It is confusing that you replace the "state" of a typical state machine with a "state operation", while the "state" is actually in a string that does not really influnece operation. Whatever you have is not a state machine.
In state operation=2 you delete from the 2D string array, but later you always seem to iterate over 9 elements (one too many to begin with) in the inner while loop.
Since the 2D string array can shrink but never grow, you might stop the program once its size reaches zero.
You write to a local variable in virtually each state, it would be more reasonable to pull this local variable write before the case structure.
The attached quick modification illustrates some of the above points. This is not a finished or even reasonable program. It would need a complete rewrite.
LabVIEW Champion . Do more with less code and in less time .
Attachments:
StateSimulatorfromEE428MOD.vi ‏64 KB

Best method for state machine design for multi-dimensional clustered data

I have an application that is collecting analog tag data(1000 points) and displaying on a graph. In each vi, I may collect data for as many as 32 channels, but only one channel at a time. Usually this is collected in numeric order, but maybe not all the time. I am also saving an "expected profile" to a file for each channel. I display both expected and actual data on the graph and select which channel to view with a ring control. My question is about how to design the state machine for best memory usage/execution speed/... If I use a shift register with a cluster datatype, that holds both 1000 point arrays, some statistical data like max/min/pass/fail/test limits for 32 channels, won't all of the u
nbundle/bundle functions use a ton of memory??? Right now I am writing the cluster data to memory tags for each channel. I use the ring control to determine which tag to read. I have the tags grouped by channel into several groups for actual data, expected data, results data,... What design methods would provide the best function using a shift register/queues and notifiers/memory tags in the tag engine?? I also use CITADEL to read the max and average as a trend display on each channel and to select a specific 1000 point dataset to view if the max and average are out of limits. Does anyone have similar applications??

It sounds as if you will be working with alot of data here so I can understand your concerns for memory management. If you were to unbundle and bundle data in your application, you are correct in saying that it will require more memory. It is somewhat difficult to get the overall picture of what you are needing to set up, but from what I can gather, it sounds as if you could have an array of 32 elements; each element a cluster of your data as well as the statistical data, and then you could index through that array to determine what to display on the graph. The shift registers will be reusing the same memory over and over so there should not be a problem there. Queues wouldn't necessarily help you in any way in this situation. Depending on how many memory tag
s you are using, you could increase the amount of memory usage required by Citadel and the tag engine, but if you are needing to write your cluster data to the database, then there is not much you can do about it. Ultimately it sounds like a pretty involved application and will require a fair amount of memory regardless to ensure smooth functionality.
In general, questions about the LabVIEW architecture and memory management are typically better answered if they are posted to the general LabVIEW discussion forum area. But I hope that this has addressed some of your concerns. Have a good day.
Patrick R.

Data acquisition in a state machine

I've recently learned how to implement state machines, but I have a question that I haven't been able to find an aswer to.
Question:
How do I record uninterupted data (presently i'm using the DAQ assistant to record a single channel at 10kS/s at 1kS intervals) without interfering with my state machine?
Background:
I have a time sensitive test setup (measuring pressure in a rocket chamber), and I'm using labview to both record a single pressure transducer as well as operate the valves (O2, N2, igniter, etc). I'm using a state machine Labview architecture (just learned how). Presently, the DAQ assistant sits in the "Idle" state, and timers (valves need to be turned on at specific times) and manual buttons control when the other states are activated. I have a 10ms timer controlling how often each state is run, and this is the root of my concern.
Main concerns:
I'm worried that:
1) I'm forced to change my data recording to 10ms intervals to match the 10ms timer, and
2) The 10ms timer will interrupt my data recording when it's in another state.
It's very important that the pressure data is recorded without interruption but that I have high time resolution in controlling my valves as well.
Thoughts:
1) Maybe I put the 10ms timer in the "Idle" state only, and this way the other states won't interrupt the data acqusition
2) Maybe there is a way to completely isolate the state machine for controlling the valves and the data acqusition. I'm not sure how to do this.
3) People on the forums have been talking about Queuing their data acqusition, but I'm not sure how this would benefit my situation.
Thanks to everyone for their feedback!

The data acquisition and state machine timer do not have to be equal, you should however have the same data write rate as you have data read rate, otherwise over the course of long running programs you can build up a large buffer of data to be written using a lot of memory, or lose data.
Your data acquisition should be continuous, the most common way of doing this is every time you receive data write it to a queue, then when you are in other states except your data write stage you simply build up data in the queue that is to be written when you enter the write state again.
Think of it as traffic reaching a set of lights:
The traffic represents the data acquisition, there is a constant flow of it always coming through, the state of your state machine is the lights, green is the data write state clearing the queue, red is when in any other state, letting the traffic build up behind the lights.
It is just important that the light is green long enough to let the traffic not build up too much, otherwise you have a jam.
EDIT: For the basics of how queues work, look at the Queue basics example from the example finder.

How can I keep a state machine readable when using large amounts of in/outputs

Hello, I am new to Labview,
Read trough the fundamentals and the
getting started and a lot of examples.
What I want to do is use a standard
state machine from the template, and add some stages, for example
orange, apple, banana. At this point I can use numeric controls to
put in the amount of oranges, apples, bananas there are. I can even
use a led to tell the user which state of the state-machine is
active.
The thing is there will be more numeric
controls and more leds and it would be nice if the code would still
be readable when there are 20 inputs and 20 outputs.
Questions
(1) It would be nice if I could use the
typedef to select the right state AND the corresponding numeric
controls and leds out of a cluster or an array kind of structure to
keep the number of wires low. Is this possible, how can I do this?
(2) I tried to put the numeric controls
into a cluster but that way I can't put the numeric control for the
apples in the upper right corner and the numeric control for the
oranges in the lower left down corner of the front panel.
(3) An example would be really nice, I
know that I saw some examples describing this problem but there are
so many examples that after a few hours of searching I haven't found
the right one yet.
Thanks in advance for the effort.
p.s. I will not use Labview to do
calculations on fruit, I am only using this to make the question
easier to understand.

I can only start a proper answer but I might as well start with that.
When I am developing State Machines I have to think about what data is used and manipulated in each state. I then have to think about where am i going to keep and manage the data. I list all of the fields that are "touched" in each state and what values are used together and which are independent form the others. After this phase of the analysis, I usually have some data structure defined (cluser array etc).
Then I flipp from thinking about the state to thinking about the data (after all this is LabVIEW and the data-flow paradigm is critical). If I see data that is only used by the State machine and is used in many of the states, then the data structure get put in a shift-register for easy access in each state. This maybe enough of an answer for your fruity question.
When i see data that is shared or only used in a handful of states then I concider putting the data in an Action Engine. Depending on how you design your AE, you can access each of the fruit totoal by name or increment etc as required.
If your app demands many fileds that are all related (can't be broken into distinct data structures) then create a cluster that has all of your values that are used by the AE. Then create an Wrapper VI for each call of the AE but only put the associated fields on the FP of the wrapper and then bundle that value into the cluster and invoke the AE.
Ben
PS: Sorry about reverting to neBulus mode but this topic could take days to cover in detail.
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

Stat machine workflow task workflow status different values on different state activity(Approval level)

i have developed the State machine workflow in which i am using default workflow task
i have added one status dropdown and that is having approve or reject that i set using workflow task drop down values
now my requirement is that when my workflow goes to different approval i need to have different status values in dropdown
for example
on manager approval state activity i need to add additional status value forward to legal
but when it moved to next activity this task status field should show only approve and reject
in summary i need to have different status values for workflow task when it moved to different state activity(approval levels)
can we set these status field of task for state machine workflow programtically as well like for different approval level of task i need different status to be set for the dropdown of task status field
MCTS,ITIL

Hi Shahid Siddique,
I have seen a similar thread from you about this issue, create custom form for the seperate form is a considerable workaround, you can have a check whether it works.
http://social.technet.microsoft.com/Forums/en-US/9baa0c32-1cde-4c58-aa7c-3568ccf0cdc9/different-approval-level-of-task-i-need-different-status-to-be-set-for-the-dropdown-of-task-status?forum=sharepointdevelopmentprevious
Thanks,
Qiao Wei
TechNet Community Support

Best way to update indicators in state machine ?

What is the best method to update indicators constantly in a SM ? ...
MY INDICATORS: I want to update the cluster of OUTPUT INDICATORS for ever new update that is happening inside the FOR LOOP (see next image). How could I achieve that ?
Abhilash S Nair
Research Assistant @ Photonic Devices and Systems lab
[ LabView professional Development System - Version 11.0 - 32-bit ]
LabView Gear:
1. NI PXI-7951R & NI 5761
2. The Imaging Source USB 3.0 monochrome camera with trigger : DMK 23UM021
OPERATING SYSTEM - [ MS windows 7 Home Premium 64-bit SP-1 ]
CPU - [Intel Core i7-2600 CPU @ 3.40Ghz ]
MEMORY - [ 16.0 GB RAM ]
GPU - [ NVIDIA GeForce GT 530 ]

Since on my machine, the second screenshot is cropped, i cannot see the complete FOR loop. You do refer to the loop writing to VISA, correct?
If so:
- Is this loop timed? If so, what is the average iteration time? Note: if this is faster than about 50ms, you should not update the indicator in every iteration as the human simply cannot see changes that fast. An average user would only see some flickering and from time to time something "readable".
- Do you update the indicators elsewhere as well?
Possible solution:
- As Yamaeda suggests: Put the indicator in the FOR loop. Works well if only this loop updates these indicators.
- Local variable: As dataflow serializes access to the indicator (variable in loop, terminal outside the state case), you wont have race conditions. On the other hand bears risks if someone introduces concurrent loops using the same indicators (variables).
- Property node "value": Same as local variable, but is bound to UI thread. Therefore, it takes more time which induces performance drawbacks. On the other hand, a property node has error in/out and is better suited to be placed in well designed dataflow programming.
- Extract UI updates from the state machine and introduce a parallel running "UI Update" loop. Refer to the Producer/Consumer template for an initial start point.
hope this helps,
Norbert
CEO: What exactly is stopping us from doing this?
Expert: Geometry
Marketing Manager: Just ignore it.

Other events interfere with abort for state machine started by an event

In the attached VI there is a state machine that is triggered by a boolean “start” change event. There is also a boolean “stop” that stop the state machine, a numeric “voltage” that has an event handler and a boolean “exit” that has an event handler.
The stop button works as expected unless if the voltage value is changed before the stop button is pressed. I was thinking this might be because there is an event for the voltage value change but there is also an event for the exit button value change and the problem does not occur if the exit button is pressed before stop.
If anyone could explain the reason I am only running into the problem with the voltage value change and/or how to properly implement the stop/abort function I would appreciate it!
Thanks,
Dave (LabVIEW 7.1)

Well that certainly solves the problem I was having! The case in a while in a case in a while reminds me of the 10-level deep if statements I used to end up when starting C programming. I guess the inner case/while are required for the state machine and the outer while is required for the Producer / Consumer. I always find myself thinking in terms of "if/then" statements and the case/comparison took the place of that.
Regardless, problem solved. If anyone has tips on how to make it (attached) look better, please post them!
Lynn, I wasn't quite sure about your instructions on passing the exit and stop commands through the queue. I went with the idea of keeping the long-running loop separate. I know I still have a bit more to work out such as use of exit button while state machine is running, and the stop button only works in between state machine iterations.
Message Edited by davey31415 on 11-27-2006 07:04 PM
Attachments:
PowerfoldMeasStat.vi ‏158 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

Trying to create multiple state machines out of same VI to monitor each cFP channel results in what seems to be shared memory between machines

Hi,
I'm trying to create a state machine which monitors a single channel on a field point. I want to monitor up to 64 channels at a time, each one with different instances of the same VI. The VI itself needs to maintain information mainly through feedback nodes both in its own block diagram and subVIs within.
All instances of this VI will be executing inside a main loop as they do not execute loops of their own as this would create 64 threads on the cFP-2200 we're using which I believe would be too much.
My attempted solution to all of this was to make the Channel Monitoring VI along with all SubVIs reentrant and "pre-allocate" for each instance. This does not seem to help as each VI seems to maintain the state of the one which ran before. Maybe I'm missing a step?
Is there a better way to approach this problem without writing a separate VI for each channel and the maintenance headache that would cause?

Hi Ben,
I actually read your document for another puzzle and it worked well, I think largely because it involved subVIs which were meant as separate threads. In that case, I used methods to alter inputs while the VI was "running."
In this case, as you know, my SubVIs are not looping inside, they are instead single calls but they do need to maintain the state at the end of their previous call, adding to the data they're tracking after they are called subsequent times. I tried the "call by reference" to call them each time. Below is a screenshot of the VI used to create the occurances and a SubVI used to execute each occurance, this subVI is embedded inside a while loop which I did not show here:
In running my tests, there still seems to be some data sharing of internal variables and feedback nodes between the SubVIs I'm calling, which I do not want. Am I approaching this in the correct way? Is what I'm trying to do even possible?

Run Code Continuously in Event Driven State Machine

Hi there, I was wondering what is the best way to run code continuously in an event driven state machine. Particularly, I am going off the JKI state machine. At the moment I put the code I want to run continuously (acquire from an instrument) in the timeout case of the event structure. When the user presses the button, the event sends the value 0 to the timeout terminal of the event structure (through a shift register). If the user stops the acquisition then the value -1 is sent to the timeout terminal. This is a tip that I took from an article by Mike Porter.
Would it be better to run this process in a separate loop? Is a state machine a bad design choice for running code continuously? I don't like my current solution because if I have another process I'll have to start putting case structures into the timeout case. Also, if the process takes a while then the event structure will take a while to respond.
Thanks for your input!

AKA_TG wrote:
Adding to that I believe Preview Queue element to read the data and Lossy enqueue to transfer the I/O output, especially if the I/O device responds slowly. This should keep your event structure polling along very nicely during I/O calls to the other structure.
I actually prefer to use an User Event to send the data to the main event structure and/or whoever else needs it. I am not a fan of the lossy enqueue (loss of data). At that point, I might as well just use a Notifier and/or global variable.

Unable to install the State Machine Toolkit in LabView 8.2

I am in the process of upgrading my version of LabView to 8.2.
I have the State Machine Toolkit working (well) on 8.0.1. I am attempting to install it in 8.2, but I have not had much success.
I can view a State Machine diagram in 8.2, but do not have the function in the palette to create one.
Any ideas ???
Thanks,
Chris.

It is a PAIN but it works.
http://digital.ni.com/public.nsf/allkb/58be852cb35237c786256a290079df39
Matthew Fitzsimons
Certified LabVIEW Architect
LabVIEW 6.1 ... 2013, LVOOP, GOOP, TestStand, DAQ, and Vison

State Machine Programming books

I just finished the LabVIEW basics I & II.Are there any third party books available that can help explain and expand on building State machines and event driven programming. Or at least cover this material in detail. Thanks in advance.
SS

I definitely agree on the Labview Style book. best LV book i read (and reread).
my experience with the other book was not enlightning, but definitely worth a look.
allow me to propose :
"A Software Engineering Approach to Labview", by Jon Conway and Steve Watts.
the book is really good, and expand on programming techniques and architecture in general. i think it is well written.
The print version has a quality problem of the figures tough (at least some editions), so i suggest you contact the authors directly or purchase the online version.
... And here's where I keep assorted lengths of wires...

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!
Go to Solution.
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

State Machine Cases revert to numbers

I have implemented a case machine using a type def enum to select the cases. The enum is a set of strings identifying each state. Initially the string for each state is listed in the case.
There is something that I occasionally do when modifying the enum which causes the case statement to display the index of the enum string. I am not able to revert back to the string display without completely rebuilding the case statement and cut and pasting my code from the old to new case statement.
I haven't been able to determine how I cause this to happen. What is it that I do to make this happen, so I can stop causing it to change? How to I make the case statement display the string state names again?

Brian,
I am using state machines a lot, and have found this as well.
There is a very good reason for it, and that is somewhat equivalent to coersion.
The easy thing to do is: (this is what I do, now)
Whenever you change the enum either by adding an item, changing the string representation of
an item, or removing an item, (and maybe disable an item) you want to copy that enum first
and make the change on the copy.
Then copy the changed enum to a place beside each existing instance of the enum, eg the assignment of the
enum to the shift register in each state. I also copy the string of the state name to someplace I can
easily see it, usually just below the case identifier.
(I usually go through all states at least twice if it is a fairly complex state machine)
I then wire the new enum to the initial input of the shift register an delete the old enum.
(At this point the case "names" become numbers .. the numeric index of the names in the original enum)
Then I go through each state and change the wire from the old enum to the new one and delete the old one.
When you get the last one changed, you will see the case identifier change back to the "names".
Then go through all the states and check that the state names are correct. (that's why I copy the names)
Then you can create your new case.
This sounds like a lot of work, but doing this methodically saves headaches!
Of course the alternative would be to design your state machine before implementing it.
And never change it! Hah!!
Dave Karon
"Brian Wells" wrote in message news:[email protected]...
> I have implemented a case machine using a type def enum to select the
> cases. The enum is a set of strings identifying each state.
> Initially the string for each state is listed in the case.
> There is something that I occasionally do when modifying the enum
> which causes the case statement to display the index of the enum
> string. I am not able to revert back to the string display without
> completely rebuilding the case statement and cut and pasting my code
> from the old to new case statement.
> I haven't been able to determine how I cause this to happen. What is
> it that I do to make this happen, so I can stop causing it to change?
> How to I make the case statement display the string state names again?

Well-oiled typical state machine

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