Shared Variable Data Integrity

I am using Network Shared Variables for a project and have a question about if there are any data integrity checks that are built into the NI-PSP protocol.
I'm more of a hardware engineer and I am just wondering if there is any way that data can be corrupted when using Network Shared Variables. I could probably just cast the data to U8 and then CRC it on both ends, but wanted to check about integrity inherent to Labview for this. Because we mainly develop medical devices, any Labview code needs to be validated if used for verification testing.
If there is NI documentation/studies on data integrity for this, I'd appreciate it if someone could point me to it.
Thanks!
Thad

Hi Thad,
The following article talks a little about data integrity when using shared variables.
http://www.ni.com/white-paper/4679/en/
I hope it helps.
Regards,
kruiz17

Similar Messages

Empty Shared Variables & Data Binding not working in dynamically called VI

Hi,
I have just upgraded a system from LabVIEW 2011 to 2012 DS2. I have a real-time PXI system running several shared variables, hosted on the PXI.
After what appeared to be a succesful upgrade I have a couple of odd issues.
1. The PXI writes test data into a network shared variable, based on a typedef of an array of custom clusters. The variable is disconnected from the typedef, as RT does not function with shared variables linked to typedefs. It seems that writing a seingle entry to the array is fine, but writing multiple entries causes the variable to appear empty.
I still need to debug this a little more, as while I was station to do so this other issue popped up.
2. I have some controls on the Host app with data binding to shared variables. The host app uses three VIs dynamically called into the wrapper VI. One of these called VIs is not able to connect to its variable when inserted in to the wrapper, but it can if run independently. The other two have no such trouble. Where I see a problem, the indication LED is grey and the mouse-over text reads "no status". What does this mean?
Any clues?
Thanks,
Ian

I have changed the Invoke Node to a Run Asynchronous node, and this seems to have fixed the data binding issue.
The other issue may be related to a bug fixed in 2012 SP1:
368648 Network Stream operations return Error 42 when data type contains nested clusters of typedefs
I am now getting error 42 when reading a particular network shared variable. This variable contains the results of measurements, in a data type which contains an array of nested clusters of typedefs. When there is a single entry in the array I can read the variable fine, but when there is more than one entry in the array it does not read and I get error 42.
I have downloaded 2012 SP1, and will see if this helps.
Ian

Shared variable data type: Can I choose an array of a custom typedef, without making the array itself a typedef?

Hi all,
I'd like to pass an array of a cluster across my network. My cluster is typedef'ed, but I'd like to avoid polluting my project with another redundant typedef.
Is it possible to use the shared variable's "From Custom Control..." option with an array, without saving the array as a new .ctl file?
Solved!
Go to Solution.

Ah, I didn't realize you were using shared variables. I thought you were just considering it as another option along with TCP/IP or UDP or something like that. In this case, you would have to create a second custom control. This control would be an array with teh typedef cluster in it. No need to make this new control itself a typedef though. Sorry, I know you were hoping for a different answer. I doubt one file will really "clutter" your project though
CLA, LabVIEW Versions 2010-2013

Shared variable, missing data, the same timestamp for two consecutively data

hello
I have a problem with missing data when I read from a network published shared variable.
Host VI:
In a host VI on my Laptop (HP with WinXP Prof.) i'm writing data to the shared Variable "data". Between two consecutively write operations is a minimum of Milliseconds waiting time. I use that because I want to be sure that the timestamp for each new data value is different then the preview one (resolution shared variables is 1 ms)
Target VI:
the Target VI on a cRIO-9012 realtime device is reading only new data in the way that it compares the timestamp of a new value with the timestamp from the last value.
Problem:
rarely, I'm missing a datapoint (sometimes everything works fine for several hours, transferring thousands of data correctly before suddenly the failure happens). With some workaround I'm able to catch the missing data. I've discovered that the missing data has the exactly same timestamp then the last readed datapoint, therefore is ignored in my "legal" data.
To sum up, the missed value is written to the shared variable in the host, but the target ignores him because his timestamp is wrong, respectively the same as the last value has, despite the host waits every time for a minimum of 10 milliseconds before writing a new value.
Note:
The shared Variable is hosted on the Laptop and configured using buffering.
The example is simplified only to show the principle function, in real I use also a handshaking and I secure that there is no over- and underflow.
Simplified Example:
Question:
Has someone an idea why two consecutively data can have the same timestamp ?
Where is the (wrong) timestamp finally coming from (system?) ?
What would be a possible solution (at the moment with shared Variables) ?
-> I tried a workaround with clusters where each data gets a unique ID. It works but it is slower than comparing timestamps and I could get performance problems.
Would it change something when I host the shared Variable on the RT-System ?
Thanks for your help
Regards
Reto
Solved!
Go to Solution.

Hi Reto,
I had a look on your modified Example.
Because the Shared Variables didn`t work like Queues or Notifiers (No Event or Interrupt when a new value has been written. And for sure the´re not possible over a network) you will see the issue, that the code is reading the values more often with the same timestamp (Polling Problematic) if the reader is faster then the writer. And because the timestamp is written with the value you´re able to program like you do. Filter out whats duplicated when you have the same timestamp.
Everything is described in here:
http://zone.ni.com/devzone/cda/tut/p/id/4679#toc1
Laurent talked about a second depth of buffer. Please have also a look at the link. Somewhere in the middle of the tutorial you see the explanations of Buffer and RT-Buffer.
Regarding your question: Would it change something when I host the shared Variable on the RT-System? --> No
In my experiences, you should consider to place the Shared Variable Engine after asking some questions regarding the application.
You will find the Answers to this 3 Questions also in the link:
Does the application require datalogging and supervisory functionality?
Does the computing device have adequate processor and memory resources?
Which system is always online?
And you`re right the smalles time interval you can see in the timestamp is 1ms.!
What you also can do is working with an enabled "timed out". This might be more performance efficient than reading the timestamp.
What I don`t know and not find up to now, is if LabVIEW or the OS adds the timestamp. It´s taken from the system time, this looks like LabVIEW is taking the value and adds it.
I hope this helps
Alex
NI Switzerland

Why string type shared variable takes more time to update in the client

I am using shared variables to share the data across a master and the client PCs connected in a network. (Network published & no buffering)
I have created an integer type shared variable(I32) and a string type shared variable (data size is 60 bytes) in the Master and subscribing to the same in the client PCs. In the master PC, I am modifying the data in this order - update the data in the string type variable and then update the data in the integer vaiable.
But in the client PCs, due to the size difference in the variables, I am receiving the data of the integer first and after that about 3-4 sec later only I am receiving the string data. Can any optimization be done to reduce this latency period? Instead of the string data type any better data type will reduce this delay?
Please suggst. Advnced thanks.

Latency has a lot to do with your network. 3-4 seconds is a long time though. This could also be due to the larget data size of your string. The integer data size is definitaly not 60 bytes. If you're looking for better performance, I would highly recommend looking into Datasocket communication or TCP/IP communication. (There are shipping example for both.)
When it comes to performance of throughput and efficiency, network-published variables are lower on the totem pole.
I hope this helps,
Kevin S.
Applications Engineer
National Instruments

My project writes accelerometer data to usb drive but shared variables do not communicate with modbus

Hi there,
I have got a program that reads input from 3 off 9234 modules on a cRIO, the idea of the program is to read this data and save it in a bin file to a connected usb hard drive, the program also uses shared variables to connect the max signals from the 9234 then send thm to a modbus slave, my problem is that althought I am now getting the correct data on the usb drive I am not getting anything down the modbus link, I attach the program for you to see, all the shared variables are on the rt low speed loop, any help would be most grateful.
Many thanks
Jason
Solved!
Go to Solution.
Attachments:
logger 2plusmodbus2.zip ‏679 KB

Hi Jasonh,
Thanks for posting your code! Due to the lack of comments on the code, would it be possible to direct me to where it sends the code to the modbus slave please?
This tutorial on How to turn a RT Target into a Modbus Slave using IO Servers may also be of some help.
Kind regards,
Tori
Student

Get data in a subreport based on a shared variable from the main report.

Goodd morning,
My question/problem is how to manage this scenario.
I am transfering 2 shared variables (pereiod from /period To, ) from the main report to a subreport and now i would like to get data in this subreport based on these 2 variables...
The problem is that i can not find the shared one in select expert icon...
Could anyone point me to solve this issue?
Thks for any help.
Jose Marin
Crystal Report XI SR3

Hello Jos,
I recommend to post this query to the [Crystal Reports Design|SAP Crystal Reports; forum.
This forum is dedicated to topics related to the creation and design of Crystal Report documents. This includes topics such as database connectivity, parameters and parameter prompting, report formulas, record selection formulas, charting, sorting, grouping, totaling, printing, and exporting but also installation and registering.
It is monitored by qualified technicians and you will get a faster response there.
Also, all Crystal Reports Design queries remain in one place and thus can be easily searched in one place.
Best regards,
Falk

Binding a shared variable to a NI-PSP data object does not work

Hi,
I want to share data between a RT-target and one or more hosts (LV 8.6.1). The network shared variables are deployed to the RT-Target. According to NI accessing shared variables from another project or host has to be done by defining a shared variable on the host and aliasing it to the NI-PSP data object on the target.
I did that and the host shared variable generated an error (0x8BBB0011) during runtime.
Next I aliased to a shared variable deployed on the host from another project. This did work.
Another thing I tried was to bind the variable from the RT-target to a display element:
This is working !!! And as you can see the path of the NI-PSP data object is exactly the same ! So what is the difference between binding a data object to a shared variable and to a display element?
Is there a bug in the SVE or am I missing something here?
The host project:
The publisher VI
Hope, someone has an answer.
Regards
Matthias Quade
Solved!
Go to Solution.
Attachments:
AliasTestWrite-RT.vi ‏8 KB
AliasTestConsumer.vi ‏8 KB

Dear Mr. Quade,
thank you for posting at the National Instruments Forum. There is a known issue with the path of the bound variable with LabVIEW 8.6.1
Please download the patch for LabVIEW 8.6.1, it should solve your problem:
http://joule.ni.com/nidu/cds/view/p/id/1255/lang/de
Best regards from Munich
MarianO

Shared variable vs. data binding

Hi,
I try to write a program which communicates motor drives through ethernet and I use OPC server and shared variables created using PLC. I created front panel indicators in a while loop with 50 ms cycle to read motor encoder position, status etc. When I try to do this with wiring shared variable to indicator and with changing the data binding property of the indicator browsing the same variable from the project library, data binding seems to respond slower than wiring the shared variable to indicator directly. Can anyone explain why?

Hi mhn05,
I'm not exactly sure why it would be operating slower. Do you have code that you can upload that benchmarks or tests the speed of these, side by side?
Thanks,
Dave T.
National Instruments
FlexRIO & R-Series Product Support Engineer

Custom data type causing trouble in deploying shared variable to RT target

I seem to be having some difficulty in using a network published shared variable created from a custom data type when deployed as an executable on an RT cRIO target. I'll start by describing why I believe this is where the problem lies. I created my RT VI in the LabVIEW development environment (LV 2012) and everything works fine. This VI is pretty simple because it rapidly devolved in to a debug exercise. The RT VI starts by simply blinking the User LED a couple of times and then starts a simple acquisition loop to read a few values off the hardware using the scan engine (while still blinking the User LED). After reading the hardware, the values are bundled in to a cluster and written to a network-published shared variable defined by a type def custom control. The custom control contains five dbl precision floats. If it matters, the cRIO RT system hosts the shared variable in this case.
So, I deploy this under the development environment and everything works fine. The LED blinks merrily along, telling me that the program is running properly. Running a host VI that reads the network-published shared variable yields the desired result. All is good.
Now I want the cRIO system to run this simple program autonomously at startup. I build it, set it as the startup VI, deploy it and then restart the cRIO target. The LED never starts blinking... the VI does not seem to run. I will spare you most of the debugging work and jump to the end. I basically "Diagram Disabled" various sections of code until the VI started running correctly as an executable. I kept reducing the size of the disabled code until only one thing was disabled: the write to the custom data type shared variable.
So, I guess my question is this: Are custom data types defined by type def'd custom controls allowed in executable RT programs? I've read through the cRIO Developers Guide, my NI Real Time Development course book and the Using Shared Variables white paper and I didn't see anything that forbade it. I know that there are some things not allowed in executables that are allowed in the development environment (front panel property nodes, dialog VIs, OS-specific calls, etc), but no mention of custom data type shared variables. Any ideas as to why my VI runs in the development environment but fails when compiled unless I remove the write to the network published shared variable?
Thanks in advance for your help!!
Solved!
Go to Solution.

Paolo,
So I thought that you meant to disconnect them in the build specification. Under the Additional Exclusions in the build specification, there is a check box for Disconnect Type Defs. I checked that box, recompiled, redeployed and it did not work. At this point I had to give and move forward, so I was going to convert the data typed from a cluster to an array. When I went in to change the data type in the shared variable pop-up from the project explorer, there was a big button under the variable definition that "Disconnect from Type Def". Clicked that button, recompiled, redeployed, restarted and everything worked great. Thank You!!
I suspect that I'll have to be careful if I change the definition of that data type (add an element, etc) since it is no longer connected to the data type. We'll cross that bridge when we need to.
Thanks again

Data Logging a programmatically created shared variable of cluster or array datatype into citadel DB

Hi,
Is there a way to log a programmatically created shared variable of cluster or array datatype into citadel DB?
I have attempted to programmatically create a shared variable of type 'double' and was able to successfully log the same into Citadel DB. In the attachment, Please refer to the attached project SV_TC.lvproj and specifically to SV_W.vi for the code that i have used (W.png file shows the dB in MAX and shared variable in NI Distributed System Manager)
However when i tried the same approach to create a shared variable 'array of double', i noticed that traces are not getting created and hence data logging isn't happening into the Citadel DB. I was however able to write and read the shared variable array without issues. The same is true with cluster datatype also. Please refer to SN_NW.vi for the code that i have used - only difference from SV_W.vi is that i have tried to create a shared variable of type 'array of double'
One observation is that if i create an 'array of double' or cluster in a shared variable library using the project explorer and deploy, i could see that these being logged into Citadel DB.
Hence i want to understand what could be done to achieve the same programmatically? Could you please advice?
Regards,
Sridhar
Attachments:
SV_TC.zip ‏3925 KB

Why is the transaction happening over remote?
Because we need the information to be on our database immediately when they submit it.
I don't know anything about streams or replication.....
The web database is run by the company that hosts our web site. We use PL/SQL to show the pages and output the html. It fetches the data the customer is requesting from our database, but I'm struggling to get the best way to insert into our database from there.

How to use a variable on columns using Oracle Data Integrator

How to use a variable in oracle Data Integrator expically on colums.

yes exactly,i selected update on new column,if i didn't select update on new colum then error is not coming regarding update.
but this time error is coming on "insert new rows".
java.lang.NullPointerException
     at com.sunopsis.dwg.dbobj.SnpSessTaskSql.bindSessVar(SnpSessTaskSql.java)
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     at com.sunopsis.dwg.dbobj.SnpSession.treatSession(SnpSession.java)
     at com.sunopsis.dwg.cmd.DwgCommandSession.treatCommand(DwgCommandSession.java)
     at com.sunopsis.dwg.cmd.DwgCommandBase.execute(DwgCommandBase.java)
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     at com.sunopsis.dwg.cmd.g.y(g.java)
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     at java.lang.Thread.run(Unknown Source).
Can u please tell me what stpes i have to follow to solve this

Using TCP or shared variable for data transfer

I am trying to send a large amount of numbers from a real-time module to a host computer. These numbers have been arranged into a large array, such as an array with 10s of thousands of points. The time critical portion of getting the information has already been done, so the data transfer back to the host VI is not time critical. I know I will need to break the large array down into smaller arrays and then reform the large array after all the information has been sent. I know how to use both TCP and shared variables with FIFO. What I am unsure of is which one is better to use for this application. I do not know what the maximum size arrays I can send through either.
Also, from what I have gathered from using LabView is that the sender has to be listening for a connection before the client opens a connection, or else it will throw an error. When I tried breaking it down into 50 points, if i did not wait long enough in the host VI or if I did not put a long enough wait function in the RT loop, and error would throw, so it would take a long time to transfer the data when it worked properly.
Any help or suggestions is appreciated, thanks.

Regarding the array size question, there is no real limit (other then the amount of memory in your system) to the size of data that you can transfer in a single block using either TCP or the Shared Variable. In your case you can easily transfer an array with 10's of thousands of data points in a single write operation. Both TCP and the Shared Variable will automatically handle breaking up the data for the maximum packet size on Ethernet and then reconstitute the array on the receiving end. In LabVIEW you will simply get back the array as a whole without needing to worrying about how the data is broken into smaller packets on the Ethernet.
I tested the attached example which transfers 400kB per block (50000 Doubles) without any problems. You do need to have the Server (in this case RT) running first before the client (Windows) can connect.
Message Edited by Christian L on 02-09-2007 11:34 AM
Christian Loew, CLA
Principal Systems Engineer, National Instruments
Please tip your answer providers with kudos.
Any attached Code is provided As Is. It has not been tested or validated as a product, for use in a deployed application or system,
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to the Sample Code License Terms which can be found at: http://ni.com/samplecodelicense
Attachments:
TCP.JPG ‏44 KB

Use of Shared Variables for data transfer from a RT traget to a desktop application

Hi,
I want to adopt the shared variables to share data in an existing distributed application comparable with the T3 Benchmark configuration in this document:
[1] http://zone.ni.com/devzone/conceptd.nsf/webmain/5B4C3CC1B2AD10BA862570F2007569EF
The current implementation uses a well tuned solution with RT FIFOs and TCP/IP communication with a desktop-PC which monitors and stores the data.
The desktop application runs with a much slower execution rate than the TCL. So the TCP/IP packets are used to buffer the data with a package size dependent on the data send rate.
To use the shared variables instead of this RT FIFO + TCP/IP implementation I need to read the shared vairable buffer at once each time the desktop application reads the shared variable.
But according to this quotation from [1]:
"With buffering, you can account for temporary fluctuations between read/write rates of a variable. Readers that occasionally read a variable slower than the writer can miss some updates."
this seems to be impossible. Am I right?
Are there any suggestions to circumvent this problem? Or are shared variables not made to share data between unsynchronized processes without data loss?
Regards Till

You can use the error-cluster to detect the end of your queue. The erroroutput of the shared variable will return a -2220 Warning, if it reads a value it has read already before. I attached a modified example and saved it for 8.2 I hope you can open it.
Attachments:
readbuffered82.zip ‏51 KB

Having trouble assigning the Data Type to Shared Variables

I have some type definitions that I need to use as shared variables. When making the shared variable, I create it and then name it. I then select "From Custom Control..." in the Data Type field and select the applicable type definition. The problem is that it displays some other type definition. Am I doing something wrong? I am using LV v.8.6. I don't recall having this problem with v.8.5.1.

Hi Hunter,
All the custom controls are set to Type Def. Since sending my question, I noticed that the system uses the first similarly used custom control and it's name. For example, I have several clusters that each have four numeric controls in them. When creating a shared variable for each of the various clusters, it uses the first custom control that was set up as a shared variable. I hope this makes sense to you. I have not had a chance to see if the shared variables are working because I have other issues to deal with first.
What troubles me is that I don't recall seeing this with v.8.5.1.
I suppose I could and perhaps should use a common type def for all similarly used shared variables.
Dave

Shared Variable Data Integrity

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