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

Subject: Re: Immediately reprocess a record [SEC=UNCLASSIFIED]
From: Andrew Johnson <anj@aps.anl.gov>
To: tech-talk@aps.anl.gov
Date: Tue, 16 Oct 2012 17:58:57 -0500
Hi Damien,

On 2012-10-16 LYNCH, Damien wrote:
> I have a record (running in a 3.14.12.2 IOC) that I would like to process
> as quickly as it can. This record is retrieving a waveform over a LAN from
> a DSO and takes a variable amount of time to process (mostly 15 - 35 ms
> but periodically around 150 ms).
> 
> Currently I am using a sequence program that does a pvPut(wfRecProcField,
> SYNC) in a hard loop to achieve this. Is this the best method? Could I
> have done this using the database only?

You should be able to do this by having the waveform record forward-link to 
itself over Channel Access, i.e. set its FLNK field to "<my-name>.PROC CA".

HOWEVER if the device support ever returns immediately without setting PACT 
and triggering the asynchronous processing delay (if the DSO gets turned off, 
or the network port unplugged maybe), then this is likely to put the IOC into 
a very fast loop which will probably hang up all CA connections to it.

One advantage of your sequence program approach is that it could monitor the 
state of the connection to the scope and the frequency that it's processing 
the record at, so it can prevent this kind of hang-up (if you code it to do 
that of course).

- Andrew
-- 
Never interrupt your enemy when he is making a mistake.
-- Napoleon Bonaparte

References:
Immediately reprocess a record [SEC=UNCLASSIFIED] LYNCH, Damien

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