Experimental Physics and
Industrial Control System

Bruno Coudoin <[email protected]> · Wed, 08 Jul 2009 15:58:13 +0200

Le mercredi 08 juillet 2009 à 11:08 +0200, Ralph Lange a écrit :
> Hello Bruno,
> 
> you should take Bob's statement as a "no".

Thanks, that is what I understood.

> Channel Access itself silently overwrites entries in the send queue, and 
> does not provide the client with information that or how many updates 
> were lost.
> If you want that functionality, you have to add the needed information 
> to the data. E.g. use a sub record and add C code that acts as a simple 
> counter and mangles a sequence number into your data. Plus client code 
> to separate things again.

I see.

> Careful: Array data is not put into the server side queue (only 
> references to the array), so using an array to add the sequence number 
> would at the same time enable you to detect missing updates and create a 
> lot of missing updates. (Probably not what you want.)

I don't understand this point. In what would it make things worse, could
you please explain me.

> Another option is to reverse client and server sides: If your data 
> source acts as a CA client, it can use CA put-complete calls that would 
> implement a handshake. That technique doesn't allow multiple 
> subscriptions to the same value, of course.

I don't need to go that far but thanks for the idea.

Bruno.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System