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shared variable write on change


I have a basic question about the SVE that I have not found a clear answer to yet in any documentation or white paper:

 

What triggers the the data transfer across the network from a shared variable engine to a client? 

 

1.The actual "read" operation in the block diagram of the client app

2. a new value written to the variable on the SVE

3. a 10ms timer? 

 

I am trying to avoid un-necessary bandwidth usage on a network and I am very interested in finding out just what triggers a network transfer when using PSP and the shared variable engine.  For instance, does the rate at which I read a shared variable in a client app have any effect on network transfer of the data? 



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Hi Garvacious,

see this link http://zone.ni.com/devzone/cda/tut/p/id/4679 under Figure 8.

 

Mike

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Thanks Mike, I have read that document before.  It seems to imply that even if there is no change to a variable's value, that there will still be a network transfer of the data after 10ms.  However, it seems kind of silly and inefficient for the engine to keep transferring "stale" data over a network when there are no reads or writes going on.  So I'm still looking for an answer to this question.


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Garvacious,

 

To answer your question(s). The Shared Variable Engine (SVE) does not transmit data across the network unless the client requests it, but the SVE does update on the server side everytime a value is changed on a shared variable. The 10ms buffer that is talked in the article that Mike linked explains how the SVE writes/reads the Shared Variables at a controlled speed to optimize network throughput. 

 

Let me know if that helped clear things up any!

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Ben Sisney
FlexRIO V&V Engineer
National Instruments
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