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

Subject: Re: scanRecord for 3.14
From: Tim Mooney <mooney@aps.anl.gov>
To: "Redman, Russell O." <Russell.Redman@nrc-cnrc.gc.ca>
Cc: "'Marty Kraimer'" <mrk@aps.anl.gov>, tech-talk@aps.anl.gov
Date: Fri, 05 Dec 2003 17:36:01 -0600
Redman, Russell O. wrote:
...
I have never looked at sscanRecord before, but just reading the
documentation it looks like a superset of the scanRecord with
> somewhat clearer documentation.  Would an sscanRecord be a direct
> substitute for a scanRecord (i.e. backwards compatible)?

No. (That was the reason for the name change.)  There are two
principal sources of incompatibility:

1) The scan record depended on an external agent to detect when
   operations it started were completed.  The sscan record uses
   putCallback for this purpose.  For some kinds of scan databases,
   putCallback completion is much easier to implement (you don't
   have to do anything) and it's certainly more bulletproof.

   However, for scans in which some of the processing occurs as
   the result of a ca_link, or a ca_monitor, EPICS putNotify can't
   trace the processing, and putCallback therefore doesn't correctly
   detect completion.  In cases like this, the database designer must
   arrange for some record, whose processing *will* be traced by
   putNotify, to refrain from firing its forward link until all the
   processing started by the sscan record is done.

   This case is kind of similar to the way the scan record operated,
   but now the external completion detector can be built into the
   database being driven by the sscan record, and instead of processing
   the scan record, it just fires its forward link to tell EPICS
   everything is done.  (This is good, because now the database will
   also signal completion to any other CA client that drives it.)

2) The detector names are different: the scan record had 15 detectors
   numbered 1...F, while the sscan record has 70, numbered 01...70.

I am puzzled, however, because the documentation explicitly states
> that it uses recDynLink which is normally distributed as part of the
> package.  If the purpose of the suggested changes is to escape from
recDynLink, how would we be better off using sscanRecord?

The plan is to convert the sscan record so that it doesn't use recDynLink. I haven't done this yet.



-----Original Message-----
From: Marty Kraimer [mailto:mrk@aps.anl.gov]
Sent: Friday, 2003 December 05 1:02 PM
To: tech-talk@aps.anl.gov
Subject: scanRecord for 3.14


The next 3.14 release will support put callbacks for database channel access links. This is being done so that synapps can remove it's dependence on recDynLink.


3.13 and early versions of 3.14 has support for scanRecord. This was removed from 3.14 because it required recDynLink. Now that put callback links will be supported the scanRecord could be easily modified so that it no longer requires recDynLink.

The question I have is does anyone use scanRecord?
Synapps provides sscanRecord which provides more functionality than scanRecord so is scanRecord still needed?


Marty Kraimer





-- Tim Mooney (mooney@aps.anl.gov) (630)252-5417 Beamline Controls & Data Acquisition Group Advanced Photon Source, Argonne National Lab


References:
RE: scanRecord for 3.14 Redman, Russell O.

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