variable engine write hangs

[RS7]

I am using the shared variable engine to bind shared variables to an OPC server (DSC/Labview 8.5)

When using read only variables, all works OK

When using a read/write variable (specified either R/W or W only in the shared variable definition), the shared variable engine hangs, and needs to be stopped and restarted for the program to work again. If the engine is not stopped and restarted, I basically get a shared variable is not located error (same as if I stopped the service manually)

I have tried synchronous or asynch writing as per the OPC Client I/O Server Advanced tab definitions (as well as In or Out of process).

Any idea why writes would be failing, but reads are working OK

[Van_L]

H RS7,

Have you tried to create a brand new variable in a LabVIEW project, bind it, set it to read/write then deploy it?
Then monitor it in the Variable Manager?

Does it give you any error at all?
I tried it on my computer, it works fine

[RS7]

I have found out some info.

All the 'Read Only' variables are as expected in the variable engine, and they update as expected when running the software

The R/W variables are also there, and update OK when using the OPC Quick client to make changes

If I run the program it all hangs and I still have to stop and restart the variable service

If I single step through the program, it works OK

I added a timed loop to minimize the number of writes to the variable, and it now works OK as well

Next question

Is there a way to prevent the variable from being written to at more than a given rate, but to eliminate the latency of having a timed loop

[Van_L]

Hi RS7

Is the Timed loop giving you latencey?
What rate do you want to write it at and what are you experiencing?
Can you provide more details please

Thank you RS7

[RS7]

a timed loop fires say every 1 sec, so I may have up to 1 sec latency between the clicking of a switch, an the action required.

If I set the loop interval to less than 500 ms, then I get long delays between the writing to the variable, and when it actually occurs. Even shorter times, I may never see the change in the variable.

I don't need fast updates, I just need them to start occurring without a delay when the event happens. In addition, if possible to have some way to allow the next setting of the variable to happen when the first one is finished.

In effect the sequence required is

1) Write to the variable

2) dissallow any further writes to the variable

3) check if the variable state has changed to that expected, and reallow variable write access

4) have a safety check, so if the write does not happen after a given time, time out, and reallow variable writes

[Van_L]

Hi RS7,

Sorry for the late reply, most of us were away for Memorial weekend.

I would suggest looking into the Semaphore vi Architecture to lock and release write to the variable.

There is a good semaphore example in Find Example in LabVIEW.

Give that a try and see if that solves your problem

Thank you