Experimental Physics and
Industrial Control System

Ben Franksen <[email protected]> · Fri, 22 Oct 2010 03:25:41 +0200

On Donnerstag, 21. Oktober 2010, Ralph Lange wrote:
>   On 21.10.2010 11:21, Steven M. Hartman wrote:
> > The ai and ao records included in base support a breakpoint table
> > facility which may be adequate for your needs. But this conversion
> > is to/from RVAL (which is an int) and VAL (which is a double). I
> > hacked a bpt record (based on the ai record) which used the break
> > point table functions included in base to do double to double
> > conversions for my needs. In this way, everything was done in the
> > EPICS database (no sequencer, no subroutine records, etc).
>
> RVALs are integer, of course - now I start remembering .... stupid
> me.
>
> For a similar application (global tune feed-forward from all ID gaps
> towards multiple families of quadrupoles) Benjamin Franksen at BESSY
> created a new record called cvtRecord to handle large 1/2D
> feed-forward tables in a generic way:

Yes. I use this record type heavily for all sorts of conversion tasks. 
It is one of the most-reused pieces of code I have ever written.

The cvt record is a lot more flexible than ao. As Ralph indicated, it is 
not restricted to functions of one input variable, but can also read 
and interpolate two-dimensional tables, i.e. calculate the output from 
from two independent inputs. Furthermore, it can load / reload tables 
at runtime. The actual loading of the table is done asynchronously and 
proceeds in parallel to the conversion, i.e. conversion continues to 
run while the table is loaded in the background. Only after the table 
has successfully been loaded is it swapped in for the old one. This 
means you can correct or adjust tables in a running system w/o having 
to stop the feedforward.

I should properly publish this code on our newly revamped website. I 
will post an announcement here as soon as I have the page up and 
running.

BTW, the csm module that implements the loading and interpolation was 
written by my colleague GÃtz Pfeiffer.

Cheers
Ben
-- 
"Never confuse what is natural with what is habitual."
                                   -- attributed to Mahatma Gandhi

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System