Experimental Physics and
Industrial Control System

"Rowland, J (James)" <[email protected]> · Mon, 21 Jul 2008 11:13:21 +0100

Thanks, interesting to see a variety of ideas for calculations.

For the inverse subarray record, is there a nice way to create 1000s of
input links (AAA->ZZZ is too many to be practical) or is the CA client
library the interface to use? Is it possible (or wise) to create dblink
structures outside the db parser so that the array of links can have the
usual attributes?

-----Original Message-----
From: Luedeke Andreas [mailto:[email protected]] 
Sent: 21 July 2008 10:30
To: Rowland, J (James)
Cc: [email protected]
Subject: Re: array calc / inverse subarray survey?

Rowland, J (James) wrote:
> [...] I'd like to do some array calculations (FFT, rectangular to 
> polar, filtering etc). I'd like the option to run at high rates (KHz) 
> which would suggest using asyn. Is there any standard for this? I 
> could easily put the calculations in the asyn layer but I can't see an

> obvious way to build a processing chain with only one link. Any 
> suggestions? [...]
My 2 cent: my "standard approach" to implement complex algorithms on 
IOCs is, to use many records connecting to the same device support.
You can use one waveform record to feed the raw data to the device 
support and another to contain the FFT results.
You may need to feed additional parameters of your FFT into the device 
support by output records or read out diagnostics into input records.
I personally use SNL only for state machines, for algorithms I prefer a 
simple device support.
This approach does not produce any overhead, since you are basically 
passing pointers.
I'm always reluctant to pass MB of data with kHz over channel access 
(but maybe I'm old fashioned here ;-)
> Also is there a standard for inverse subarray? I'd like to combine 
> 100s of scalar PVs into one waveform. [...]
I agree that an "inverse subarray" and a "waveout" record would be nice 
in EPICS base.
Of course one can do both with a device support, but I would find a 
record implementation cool.
Has somebody developed any of both records? If yes: how about adding it 
to base?

Andreas

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System