What determines Finished Late? flag in timed loop?

I've monitored the Global Start Time (and Iteration Start) from iteration to iteration in a real-time loop. These delta time between iteration starts varies beyond my loop rate (e.g. 1680 usec between iteration starts with a 1666 usec period), yet the Finished Late? flag does not indicate true. Maintain Phase is TRUE, Discard Missed Periods is FALSE, Deadline and Timeout are default (-1). So why does Finished Late? not fire when all clocks tell me the loop was late?

A (very) rough example is below and some results (run on an RT controller). I guess the loop didn't "finish late" but it appears that they can (and usually do) start (significantly) late or early so am I missing something? This jitter is there even when the Chart and Stop button are removed from the timed loop (e.g. using RT FIFOs to send the data to a chart loop). To some extent I answered my own question - my loops are not "finishing late" so the flag isn't set, but apparently the jitter here is significant. In this simplistic example, I saw jitter of +/- 4 ticks (usec) when the CPU usage is at barely 1% per core (dual core) - so is the RT jitter just bad in general or is it the 1Mhz clock or ???
Attachments:
RT Loop Timing.png ‏8 KB
RT Loop Timing Graph.png ‏14 KB

Similar Messages

What is error -1418 on a timed loop?

Has anyone ever gotten error -1418 on the error terminal of timed loop? It only executes once and I'm trying to run it on a cRIO-9004.
There's nothing in that range listed under the timed loop error codes.
http://zone.ni.com/reference/en-XX/help/371361F-01/lverror/timed_loop_error_codes/
Thanks as always,
Jim
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Hi Jim,
I belive this is what you were looking for:
Timing Sources Available for LabVIEW Timed Loop by Platform
Kristen H.

Timed loop in LabVIEW DLL does not exit nicely

Hello! I have what I think is a simple timed loop in LabVIEW that exits after 100 iterations by throwing an error, and letting the loop "stop on error". This works fine when run in the regular LabVIEW environment, however, when compiled as a Dynamic Linked Library (DLL) and called from LabWindows it forces me to terminate execution, rather than exiting nicely. What's more, it seems to quit the actual Virtual Instrument call just fine and proceed to the next line of code, but when my main() function in LabWindows completes there must still be something not cleaned up that is causing it to not exit nicely. Any ideas?   I've tried adding a call to QuitLabVIEW and that doesn't seem to do it.
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Attached is a picture of the timed loop.
Below is an excerpt of code from LabWindows:
int main ()
CallMyLabVIEWDLL(); //This line successfully launches and closes the window for my LabVIEW virtual instrument
MessagePopup ("My Title:", "This happens after the call to your LabVIEW DLL");    //This popup shows up - indicating the call to the DLL has completed
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    return 0;
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Attachments:
LabVIEWTimedLoopDoesntExit.png ‏103 KB

Update: I tried the simplest possible "While" loop and it works. If I replace it with the simplest possible Timed Loop, it doesn't. (See attachments.)
The only thing I could find in a search for why a time loop would break a dll is a patch for lvalarms from LabVIEW 8.5.1 .... I'm running LV 2010 so I don't believe that's an issue. Correct me if I'm wrong?
Thank you!
Attachments:
Doesnotwork.png ‏43 KB
DoesWork.png ‏9 KB

CVS-1458RT - ISO I/P triggered timed loop

Hi everyone,
I am developing a real-time machine vision application on a CVS-1458 RT.
What I am aiming is a timed loop that is triggered via external clock (in my case a photoelectric sensor connected to an ISO input). All examples I can find are related to DAQmx devices, nothing related to visionRIO.
Question 1: Is this the best way to construct the acquisition loop? I want it to be condition based as to free-up the CPU from continous polling. If not, wht is the best way ?
Question 2: If the above method is OK, how can I setup the input node of my timed loop in a way to implement this ?
Thank you,
Omar

Hi Omar,
I was able to find some Vision-RIO examples in the Example Finder of LabVIEW. If you open LabVIEW and navigate to Help>> Find Examples.
In the Example Finder in the Browse tab navigate to Hardware Input and Output>> Vision Acquisition>> Vision-RIO.

Unable to click on buttons during timed loop .

Hi !
I have a timed loop with a cadence set by user . And when the loop is running, I can not push any button of my GUI to stop this....
I have to wait until error or I stop the run.
I can't put the diagram it's too big and I think I haven't the right but do you have some ideas ?
Ask me for more details .
Thanks
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bejard wrote: The Timed loop is just in an event structure and I set 10 ms or 100 ms .
The program is running correctly (with this Timed loop of 10ms/100 ms) as the beginning but I still can't push any button or change tabs during the loop .
You should not have long processes inside of an event case. What is supposed to stop your timed loop?
I think you have the "Lock front panel until event case completes" option turned on. This will not allow you to press anything until everything in that event case (including the timed loop) completes.
In my experience, using a timed loop in a Windows system is a complete waste and often adds more overhead and issues. Instead, I really think you need to change over to use a State Machine. When the button is pressed, you just tell your state machine to go into the state the runs some of the code inside of your timed loop. You can use the state with the event structure to time your loop. So you can go back and forth from your event structure state to your processing loop. Just set the timeout on the event structure to whatever loop rate you actually want.
There are only two ways to tell somebody thanks: Kudos and Marked Solutions
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LabVIEW RT, Timed loop, finished late, Call by reference

I have a timed loop triggered by the sample clock of a DAQ-Card. The sample Clock is 8 kHz and the loop will run with dt = 4. Normally the loop is running without finished late[i-1]. But from time to time it happens that the loop is running extremly longer which means instead of 0.5 millisec it needs 4 - 5 millisec. It seems this doesn't never occur while accessing DAQmx.
The application uses plugin technologies and some of the VIs in the timed loop are preloaded and called by Call by Reference.
Does those VIs inherit the priority, execution system and CPU of the timed loop?
The application is running on LV RT 2009 on a Dual core PXI-Controller. The timed loop is bound to CPU 1. There is no difference runinng the application from the development environment or as a startup application.
For the measuring test I modified the application in a way that I don't have:
disk access for storing the result file
TCP/IP communication
Controls on the front panel of the top level VI
Waldemar
Using 7.1.1, 8.5.1, 8.6.1, 2009 on XP and RT
Don't forget to give Kudos to good answers and/or questions

To keep you informed:
I stripped the application and have left only the measurement storing module and the timed loop. The loop was using the microsecond timer running each 500 µsec. Additional all Non-Real-Time modules were loaded and only one module creates a XML string and sends it to the communication layer which will drop it because no TCP/IP port is open. The creation of the XML string is done each 300 ms.
In this case I don't have any finished late iterations
Next I added the DAQ Module. Now I get finished late again but with a lesser frequency as original.
I removed all unnesseccary tasks from the DAQ moulde leaving one task for a PXI-4204 for using as the clock source for the timed loop. No I get finished late seldom.
I removed the module which will send the XML string and I don't get finished late.
Next I was adding code to see memory allocation. I can when memory allocation is changing but it is not related to the finished late iterations.
Next time I have the chance to do more tests I will see which DAQ task triggers the finished late iterations. I have one AI task on a PXI-4204, 4 Counter tasks on a PXI-6602, 1 DI task on a PXI-6514, 1 DO task on a PXI-6514, 1 DI task on a PXI-6259, 1 DO task on a PXI-6259, 1 AO task on a PXI-6259 and 1 AO task on a PXI-6711.
The AI task on the PXI-4204 is running in Continous Sampling (Single Point HW Timed is not supported), all other tasks exept the DI and DO are Single Point HW Timed.
Waldemar
Using 7.1.1, 8.5.1, 8.6.1, 2009 on XP and RT
Don't forget to give Kudos to good answers and/or questions

How can I count the number of times a timed loop finished late?

I am getting occasional timing errors in a timed loop under windows XP and would like to count the number of errors, but I can't find a simple software counter vi

The timed loop has a terminal (boolean) to indicate if the previous iteration finished late. Just increment an integer shift register if this happens.
The attached shows a very simple demo (LabVIEW 7.1).
LabVIEW Champion . Do more with less code and in less time .
Attachments:
LateCounter.vi ‏76 KB

What's wrong with the IOS5 download, it downloads and then after its finished it says server timed out, how do i sort this out

What's wrong with the IOS5 download, it downloads and then after its finished it says server timed out, how do i sort this out?

The Firefox versions which come with many Linux distros have the default Mozilla Firefox updater disabled and use the distros built-in updater.
See this - http://linuxforums.org.uk/netbooks/install-firefox-6-on-an-acer-aspire-one-running-linpus-lite-linux/

What is the best/most effective way to dynamically build a timed loop in LabView?

I am relatively new to labview (not to code in general) and am looking for the "LabVIEW" way to dynamically build a timed loop. This is what I am trying to accomplish:
I have several heaters controlled through labview using Labview's PID toolkit. This works great. I have no issues with DAQ in general. However, throughout an experiment, I want to change the set point of each heater. I could set this up fairly easily using either a timed loop or the wait vi if I knew exactly how many different set points there would be.
If possible, I would like to be able to read in a config file that includes the different times and set points for all heaters and dynamically create a loop that can handle this. I have tried using the Elapsed Time vi with an array of time targets; however that didn't seem to work.
Has anyone been able to do this? Does anyone know where I could learn about using LabView in this manner? All help is appreciated.

DHagan wrote:
I am relatively new to labview (not to code in general) and am looking for the "LabVIEW" way to dynamically build a timed loop. This is what I am trying to accomplish: I have several heaters controlled through labview using Labview's PID toolkit. This works great. I have no issues with DAQ in general. However, throughout an experiment, I want to change the set point of each heater. I could set this up fairly easily using either a timed loop or the wait vi if I knew exactly how many different set points there would be. If possible, I would like to be able to read in a config file that includes the different times and set points for all heaters and dynamically create a loop that can handle this. I have tried using the Elapsed Time vi with an array of time targets; however that didn't seem to work. Has anyone been able to do this? Does anyone know where I could learn about using LabView in this manner? All help is appreciated.
Write a tab-separated spreadsheet file makes it easy to use the write/read from spreadsheet files. Assuming you have a 2D-array of your times and set points it's just a question of setting up a for-loop going through the array row-by-row and extract the elements (expanded index array) to set your points and wait time.
/Y
LabVIEW 8.2 - 2014
"Only dead fish swim downstream" - "My life for Kudos!" - "Dumb people repeat old mistakes - smart ones create new ones."
G# - Free award winning reference based OOP for LV

What is wrong with this (timed loop error)?

I can't figure out why the timed loop is not starting and I receive an error -805 message. Any idea?
Thanks,
Ben64

Hi Ben64,
There's no obvious problem.
I tried the same and it works perfect.
So there must be a problem under the cover.
I have 2 suggestions.
1) There is a problem with your wiring -> the Error wire is not connected to the loops error out -> close timing source is executed before the loop is executed (Are you sure the loop doesn't even start ?)
2) Labview often uses Names to identify items (queues, images, semaphores,..... timing sources(?) )
I tried to open and close another timing source with the same name.
Et voila : I'm able to get exactly the error code you mentioned.
Is it possible you use the same name for a second timing source and this one is closed prior to executing the timed loop you've got problems with ?
Best regards,
Balze
Attachments:
timed_loop_2010.vi ‏37 KB

Timed loop and CPU usage

Platform is WIN_XP Pro and machine is a P4 at 2.5Ghz with 512 Mb ram.
LV7.1 + PCI 6229
I am using 50ms Timed loop for running a state machine inside it
and also a whole lot of other things like reading / writing
DAQMx functions; file I/O functions and such. As the
project involves a main and sub-panlel set up local variables
could not be elimnated fully and there should be something like 150 of
them. But not all are accessed always - maybe about 15 of them at any
given time depending on the SM staus.
Problem :
Once started the "Finished late" indication is off and
the actual timing alternates between 49 to 52 ms. The CPU
usage is around 25%.
But as time goes by, the system gets unstable : After 15 minutes
or so, the Finished Late indication is always ON and the CPU usage is
gradually tending towards or exceeds 100%.
Obviously the machine control timing now gets affected and things slow
down badly. Closing the application ands restarting repeats the above
cycle.
I am at a loss to understand what is happening ? WIll
breaking down the single Timed Loop to multiple ones help ? WIll
that be an efficient way of parallel threading ?
I can post the code but its quite large and will do it as a last resort.
thanks
Raghunathan
Raghunathan
LV2012 to Automate Hydraulic Test rigs.

Hello,
It sounds like an interesting problem. It would be worth some experimentation to figure out what's going wrong - attempting to decouple major "pieces" of the code would be helpful. For example, you could try breaking your code into multiple loops if that makes sense in your architecture, but perhaps you could even eliminate all but one of the loops to begin with, and see if you can correlate the problem to the code in just one of your loops.
Another concern is that you mention using many local variables. Variable read operations cause new buffer allocations, so if you're passing arrays around that way, you could be hitting a problem of forcing your machine to perform many allocations and deallocations of memory. As arrays grow, this can be a bigger and bigger problem. You can use other techniques for passing data around your block diagram, such as dataflow if possible (just simple wires), or queues where dataflow can't dicatate program flow completely.
Hopefully looking into your code with the above considerations will lead you in the right direction. In your case, removing code so that you can identify which elements are causing the problem should help significantly.
Best Regards,
JLS
Best,
JLS
Sixclear

While loop inside a timed loop

Hi everybody!
   I'm using:
       - LV 7.1 + RealTime;
       - compactFieldpoint;
   I've noticed a strange behaviour, when I put a while loop inside a timed loop. Let's fix timed loop with these settings:
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       - 1 ms period (yes, I know it's short....)
       - offset 0 ms
       - Phase 0
       - Discard missed period (ON) and MAintain original Phase (ON);
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   If inside this loo, I put a traditional while loop, waiting (say) for an event to occur, and if this event does not arrive, my cFP-2020 hangs! I mean, it becomes unreachable for the debugger, and, more, if I run a ping to it's address, after some cycles it becomes unreachable also from ping!
   Clearly, this code statement lock the fieldPoint, because if I remove the inner while loop all works.
I know that with 1 ms period, timed loop always finishes late, but I set to discard missed period and timeout to -1.
   It seems to me that sometimes Timed Loop add heavi overhead to programs, I'm turning to all while loop based tasks, even if my application has to be real-time!
   Advices welcomed! Have a nice day!
graziano
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I think the issue here is that putting your while loop inside a Timed Loop increases the priority for that task. Timed Loops can have dynamic priorities set over eachother, but they all run between Above Normal and Time Critical priority. My guess is that the debugger and built-in TCP functions run at Above Normal priority or less. This means your cFP isn't hanging, it's doing what it thinks is best. It's trying to finish this task before handling any lower-priority tasks.
The suggestion to put a Wait function in your loop is an OK one. Keep in mind that you can actually set your wait time to zero instead of one and get the same positive benefit of handling other tasks. I would also suggest that you might look into waiting for this event in a lower priority (non-Timed) loop, and then transmit the appropriate data to your Timed Loop using an RT-FIFO or something. That might give you better handling. Just a thought....
Jarrod S.
National Instruments

Using timer/counter with PCI-6221/USB-6210 to control timed-loop VI

Dear all,
I need to ask about two devices and one of their functionalities, PCI-6221 and USB-6210. For our NI-based system, we need to control some timings in a Timed-Loop vi, for that currently we are using PCI-6221 and we give external TTL signal (at 1 kHz) to it,
recenntly we need to make some changes and for that we found USB 6210 DAQ to be more suitable, but we need to clear ourselves on some specific things.
Can the counter/timers functions available in the either PCI 6221 or USB 6210 can be used to control the Timed-loop VI by giving external clock or by using their own internal clock source?
Although we are using external clock with the PCI 6221 but we want to know about the usage of their internal clock, also are controlling timed-loop also possible for USB-6210
Also... What if we use the RTOS, are they still able to control the timed-loop VI without giving any 'EXTERNAL CLOCK' and using the internal clock sources of the DAQs
Waiting for reply,
Bests,
RaJaf
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Ben,
I having read previous email which I send earlier with general overview, we discussed in more detail within our team and I am giviing the specific answers.
Please check in RED the most recent answers. Blue are the questions/suggestions by your side.
1.    Using Internal hardware clock of PCI-6221 would enable us get rid of external clock, but how to divert the internal hardware clock to the current settings. Any idea (can you provide us with some reference manul for otherwise). I mean is there some flag-bit etc. or VI
2.       Is it also meant that with the installation of RTOS the timed-loop can directly get the timing source from the internal hardware clock PCI-6221? --- How???
3.       In order to make desktop to work as RT system, what is the hardware (motherboard, processor, etc..) requirement? What are the LabVIEW modules (specific name) that needed to be installed? Our platform is LabVIEW 8.6. (Currently we have windows-7 with i7 core processor)
What kind of application are you intending for this system? ---- high-speed laser scanning system.
Are you most concerned about accuracy, speed, or responsiveness? To control the laser mirror scanner to move at 1 kHz or 2 kHz speed. On the other hands, using PCI-5105 (128 MB memory) as a DAQ for real-time/on-the-fly data processing.
Bests,
RAJAF

Unable to run Timed Loops

Bit of an odd one that had me scratching my head.
I have a development system consisting of a PC running a 7842R, acquiring analogue and digital data from the FPGA, loading it into a shared variable, and reading it out within a timed loop on the host as one parallel loop in a producer-consumer architecture.
All's well until one day last week when I noticed my host VI becoming unresponsive.
After a bit of digging, I find that the timed loop doesn't run at all. Replacing with a while loop with a wait at least allows me to show that the error is timed loop related, but it's not a viable long term option for me. Creating a new project and a new VI with a simple timed loop showed the same behaviour.
A restart of the system, and rerunning the same VIs, and no problems since.
So, questions:
1) Has anyone else seen this behaviour?
2) Any idea what causes it? A service crashing, for example?
3) Is there a way of recovering without a reboot? If it's a service crash, I'm hopeful.
The system will eventually form part of a production test environment, hence the query.
Edit - also, wiring error terminals of a timed loop is a good way of highlighting errors of course.
FWIW, LV2012 SP1 32bit, Win7 64bit, Core2 Duo, 4GB RAM, tassels from the handlebars etc.
CLD

The timed loop is used to read all elements from a DMA FIFO and load them into a buffer FGV, which spits out packets of N samples long once they've assembled within the FGV. Ordinarily, I'd do this with a timed while loop and be perfectly happy to do so. However, the elements are actually an interleaved array, meaning that I have to demux them in the correct order that they were loaded.
I use timed loops for a number of reasons: on my current Windows host, I've found that using a while loop has caused me more problems with respect to disordered packets, and that at least with using multiple timed loops (two, at most), I can assign priority to the acquire loop. Finally, it's also a development platform, and will be deployed onto an sbRIO once the electronics integration is finished in a week or two!
W.r.t. system resources, there's very little else running on that system, but that doesn't normally stop Windows
I recognise it's not ideal to run a software timed loop under Windows, but when you cannot run a blank project with Optimizing timed loop rate.vi from the shipped examples with nothing else running, it makes me curious to know why!
CLD

Timed loop not starting - works after closing and opening project

Refer the image below - a simple timed loop should run when the Run button is pressed. What happens is that the parallel vi runs (see arrow) but the vi inside the loop doesn't. Both vi's shown run forever (i.e. the timed loop is only used to specify the CPU).
When I press the Abort Execution button, strangely it can then be seen that the execution highlighting runs into and through the timed loop and probe 50 is updated.
This sorted itself out after I closed the project and opened it again so its not a critical issue - was simply wondering what could cause this?

That program looks kinda weird.
First of all, avoid to use flat sequence structures whenever you can, or use it only when you are going to initialize something, or when your program has an specific sequence.
I think you have a problem the way you are conecting the subvis. Remember that in LabVIEW, the flow of the data will determine the order of execution, and in your case, the conections looks kinda weird.
I have a question; Do the subvis need to run simultainously?, or what do you need to do exactly

What determines Finished Late? flag in timed loop?

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