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<== Date ==> <== Thread ==>

Subject: Re: Callbacks and the PCAS question.
From: Brian Tieman <tieman@aps.anl.gov>
To: Mark Rivers <rivers@cars.uchicago.edu>
Cc: tech-talk <tech-talk@aps.anl.gov>
Date: Tue, 20 Feb 2001 09:10:37 -0600
Mark,

Of course you can do it this way.  You can also use the client wait feature of
the scan record directly.

The problems I have with this are: 1)  It implies the server tool is deficient
since not all server functionality is supported properly. This is a general
problem for us since the server tool is currently a generic tool integrated
into several acquisition systems and at least one motion control system.  2)
It also means you have to have a VME crate in the loop to support the Busy
record.

I've known ways around the problem for quite a while, but since the interface
I've built around the PCAS is in general use now, I think I really need to
solve the problem rather than work around it.

Brian

Mark Rivers wrote:

> Brian,
>
> The way we do this is to make the data acquisition program be a channel
> access client, rather than a channel access server.  The scan software
> writes a 1 to a local "Busy" record, which is just like a binary output
> record except it does not do the forward link until its value goes back to
> zero.
>
> The acquisition program monitors that Busy record. When it goes to 1 it
> starts collecting data.  When the data acquisition is done it sets the Busy
> record back to zero, which lets the scan continue.  This method does not
> have a problem with a 30 second limit.
>
> Mark



References:
RE: Callbacks and the PCAS question. Mark Rivers

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