Re: Scan question

[John Sinclair <sinclairjw@ornl.gov>]

Actually, when I ported the tandem controls to EPICS, I modified a 
couple of the
standard records (ai, ao, mbbiDirect, mbboDirect) to be able to 
manipulate the scan value inside
the record's own code. The remote I/O throughput was too low to have all 
the records scan at
a rate fast enough to make I/O sufficiently responsive during beam 
tuning. In the old system
(no network), several process variables could be assigned to knobs and 
meters which would
cause them to be processed at a higher scan rate. So I used the same 
scheme. I added a
fastscan and slowscan field to the database along with several fields to 
manage the assignment
operation. When the PV was "assigned" (to a knob or meter, in this 
case), an assignment reference
count was incremented. When deassigned, the count was decremented. When 
the count became
non-zero or zero, the scan field got the value of fastscan or slowscan 
respectively. In this case
I obviously needed the record to manage the scan value rather than some 
external agent.

Ain't EPICS wonderful.

John Sinclair

Mark Rivers wrote:
> I think it would be a bad idea for a record to change the SCAN field.
> That is something that you should let the database designer do.  They
> may want to use your record in ways you never thought of.
>
> However, if you really want your record to process again when something
> happens then the record code can request reprocessing without changing
> the SCAN field.  There are several ways to do this (scanOnce,
> processRequestProcessCallback) depending on the application.  Look at
> the Application Developer's Guide.
>
> Mark
>
>
>   
> > -----Original Message-----
> > From: tech-talk-bounces@aps.anl.gov 
> > [mailto:tech-talk-bounces@aps.anl.gov] On Behalf Of Heinrich du Toit
> > Sent: Thursday, July 12, 2007 9:05 AM
> > To: TechTalk EPICS
> > Subject: Scan question
> >
> > Can I change the SCAN field at runtime?
> > E.g. inside my own custom record.
> >
> > Some devices normally needs only be scanned say once a sec or every 5
> > secs. But then when you change the value you want the scanned 
> > faster at
> > say 0.2 secs.
> >
> >
> >
> >
> >     
>
>
>

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