Event structure doesn't handle all events from external DLL source

Hi!
I use a DLL, wich handles an USB CAN transceiver device, and generates LabVIEW user events with extcode.h and PostLVUserEvent() function.
In my vi I use an event case structure to handle theese external events. The problem is, that if the events come too frequently, then it cannot handle all events.
The vi contains a couple of parallel while loops which process the incoming data from the external event.
In another application I use the same architecture, and that works fine. This one is more complex.
Do you think I have reached the limits of the program? Or what else can be the problem?
I have tried to use a queue in the event structure, it helped a little, but yet, not all the events are handled. My external DLL sends all event, so the problem is not there.
Thanks in advance!

Hi Wasz,
Thanks for the post and I hope your well.
It is not possible for the event structure to miss events - it simply queues them up. To keep the event structure 'in time' with the code you must ensure the code to execute in each event is minimal to allow the event structure to handle the next event.
Please see this two links:
event structure buffering: leading to,
How to avoid built-up for "cursor move" events? : where somone is trying to avoid handling all events.
What sort of events are not being handled? Could it be an issue your events are not configured correctly? Maybe if you could produce a small example in LabVIEW code, so we can just test the event structure configuration... someone working around the external dll call - which you seem sure is working correctly.
In terms of queuing to process the events in other loops is certainly an option to speed up the event structure. To do this, use a produce/consumer design pattern.
hope this helps,
Kind Regards
James Hillman
Applications Engineer 2008 to 2009 National Instruments UK & Ireland
Loughborough University UK - 2006 to 2011
Remember Kudos those who help!

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LabView user-event from external dll source

Hi!
I'm dealing with the following issue:
I use a CAN sniffer device, wich sends data over USB to a PC. The main goal is to create a vi that can process the incoming data. I already have a vi wich works with polling mechanism. It calls external DLL functions with the "Call library function node". The main problem is the polling mechanism.
I would like to recreate this vi so that it would work event-driven. I have an other application, written in C++, that does the same thing, and it gets interrupts from a DLL, when a new data is available in the input buffer.
The callback mechanism is implemented in the DLL.
In LabView I would like to do tha same thing. There is the "event case structure", but there is no option for defining such user-events, that i would prefer.
I have found a similar topic, there the solution is "occurrences". The occurrence is called from a DLL, too. But this solution uses the "waiting for occurrence to set", that is an endless-loop-like thing.
The other thing I've found is the ActiveX and .NET events. I don't know, probably that is the solution.
Anyway: is there a possibility to create such events, that can be generated from a simple external DLL and can be handled by "event case structure"? How should I do this?
Or how NI does this? I mean that NIs DAQ cards must use some similar methods for data processing. Is there some tutorial or support about it?
Thank you for your answer!

2716jag wrote:
Hi Wiebe, From your answer i have a doubt that What it exactly means "If the dll is used from within LabVIEW". Also i want to know Is there any way to access the functuions defined in the .SYS file in Labview Environment. Regards,Jagan Can you be a litte more specific with your first sentence. I have no good idea what you mean. A .sys driver is usually a kernel device driver. This driver has to be started and run in the kernel subsystem which LabVIEW can not access directly. Such a driver is initialized using the CreateFile() Windows API. The returned handle is then used with other API functions such as ReadFile(), WriteWile(), DeviceIoControl(), and finally CloseHandle().Theoretically you could call all this APIs directly from within LabVIEW using the Call Library Node. In practice you do not want to do this even for fairly simple kernel drivers since the parameters for those APIs do get fairly complex in most cases, and you usually do also want to have some sort of asynchronous operation using events or such to make the driver access user friendly. All these things are most easily handled in a user space DLL written in C that exports a more LabVIEW friendly API that you can then import into LabVIEW using the Call Library Node. Usually most kernel device drivers do come with a accompagning user space DLL already, as this is the only sensible way of accessing such a driver. So you can usually look for the documentation of that user space DLL API and go from there trying to import that into LabVIEW using the Call Library Node. Even then it may not be easy at all if that API uses complicated function parameters and even completely impossible if it uses callbacks or such, requiring you to write a so called wrapper DLL that translates between the native API and a more LabVIEW friendly API. You don't have to believe me but I can guarantee you that if writing such a user space DLL or wrapper DLL is beyond your capabilities, trying to go directly about accessing the Windows APIs in LabVIEW to access a kernel device driver is going to make you squirm in real pain. And those knowing how to write such a DLL would never even consider spending the time to try to access a kernel device driver directly from LabVIEW. Rolf Kalbermatter

Find Control in Event Structure doesn't show the object when it is not in the frontmost Tab page [Bug Report, LabVIEW 2012]

When you are looking for the control/indicator handled by a case in the Event structure, you can use the contextual menu item "Find Control" (doesn't distinguish between control and indicator, BTW).
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I did not. Is there any better chance for it to be caught there by a NI eye than it is in the LV forum? I though these threads were deemed to gather bugs/features that had been already acknowledged by NI with a CAR number.
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Event structure doesn't register local vars

I have a gif of a basic FPGA topology that I want to show some loopbacks in. As the user clicks on the booleans, vertical lines should appear, then disappear as they click them again, showing the current loopback topology.
To conserve resources, I opted to use an event structure. So far I have set it up for the RX_FAC and RX_TERMXCO4AU loopbacks that you see in the upper left of the picture.
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This will make a lot more sense if you run the attached simple VI. Right now, events only exist for RX_FAC and RX_TERMXCO4AU, but it's sufficient to explain the problem I think.
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Solved!
Go to Solution.
Attachments:
loopbacks.vi ‏55 KB

bmishoe wrote:
I learned something new today...
One more thing you can learn, When you are passing an array input to a For loop with 'Auto indexing' enabled, you need not wire anything to For loop's 'N' terminal.
In other words:
If you enable auto-indexing on an array wired to a For Loop, LabVIEW sets the count terminal so you do not need to wire the count terminal.
In your code, you can remove the 'Array Size' nodes.
I am not allergic to Kudos, in fact I love Kudos.
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Can JFC handle all event of html element

I was just going through with JSF spec.
I have some doubts .
Can JSF hanlde all the events related to html element like key down , onclick etc, on form load.
Instead of writing heavy javascripts for this on client , can i handle all this on server side with JSF.
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My Library Doesn´t Show All Events

Hi!
After a data crash my library shows only half of existing events. The "missing" pictures / events seam to be okay - I can open them in Finder.
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TIA HJ

Try these in order - from best option on down...
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TD

Event structure and automatic queueing of events.

I have found out the long way that the event structure queues all the events taken place while it has been executing yur most current event.
In other words... I understand why the locking of the front panel is an automatic option that is selected. As it will prevent you from queueing more events, and causing yur program to execute endless event structure runs, when you wanted it to stop 15 button presses ago.
case in point.... is in this simple VI i attached.
My question is ... is there a way to turn off this automatic queueing of events??
Attachments:
EventStructureHUH.vi ‏53 KB

Well ... the problem for me... was, for example, in the VI I posted....
The OK button in the VI I posted, has an event triggered to it in the event structure.... So when I enter that loop after hitting the enter loop button... it registers those OK clicks...
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Basically I wanted one button to control the termination condition of the little loop, but also have an event in the event structure associated with it, so basically one button to exit the little loop AND the big loop.
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I just wasnt sure if there was another way around it... it was tough to figure out what was really happenening in my code... took my about an hour or two to track down.
EDIT: Yea.. thanks for the reply.... as for the comments in my code... yea, I get a little crazy towards the end of the day... after 6-8 hours of straight labview programming.
Message Edited by MJBrehm on 06-30-2006 02:21 PM

Simple example - Break FOR loop inside an event structure based on Front panel event change.

I am running a for loop inside a state machine architecture that contains a FOR loop. How can I break this For loop based on Event change in front panel ??
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 ]
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Attachments:
Case inside Event 3.vi ‏19 KB
Case inside Event.ctl ‏6 KB
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Okay. Accpeting that the design is not favorable and not advantageous when my program expands. I have begin to follow producer/consumer programming architecture.
Please find the attached program which is a simple producer consumer with event structure. I wonder how could I stop looping around the producer and consumer loops over and over again. I am pretty sure that this ENQUEUE ELEMENT loops back to the consumer loop and starts from begining.
I hope my first program in PC architecture with State machine and Event structure is correct.
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 ]
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Case inside Event 3.3-ProducerConsumer Event.vi ‏25 KB
Case inside Event.ctl ‏6 KB

Can I use Ctlref in a event structure with a mouse up event?

I have a large number of controls on a front pannel. I'm using a event structure that triggers the motion of a given motor when the corresponding control is pressed. However, I would like to avoid creating N mostly identical events, so I was planning on using a mouse down event on the front pannel, then retrieve the control reference using the Ctlref node (with gives "Reference to the control on which the event occurred" according to labview manual) and scan a array of references to find out which motor is supposed to move. However, it seems that this node does not appear (contrary to what the manual says).
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Solved!
Go to Solution.

Bad luck for you. Mouse down on panel does not have the control refnum as it is not operating on a control. Mouse down on a control does have it and since you can configure mouse down events on several controls in the same event case, it provides also a control refnum so that you can still operate on the control in question.
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CIT Engineering Netherlands
a division of Test & Measurement Solutions

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Hi ,
I started the change suggested in the link shared by you, but got stuck at a point,
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Yes, BCS needs a UID. This is so it can figure out changes over time to a single record. Otherwise all changes to a row could be a potential new row without BCS knowing any better.
Yes, or just have it run off the composite key instead of the field you're using now.
Nope, BCS needs a UID field like in answer 1 :)
Good luck!
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Event structure doesn't handle all events from external DLL source

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