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<== Date ==> <== Thread ==>
Subject: Re: How to implement simple control algorithm (one more question)
From: Andrew Johnson <[email protected]>
To: [email protected]
Cc: "Ilya V. Kitaev" <[email protected]>
Date: Mon, 5 Jan 2009 11:13:35 -0600 
On Sunday 28 December 2008 09:02:47 Dalesio, Leo wrote:
> YOu can make the strings as long as you like. You just can't set or get
> them through channel access then - a 40 character limit. I'm not sure that
> it handles this properly. Jeff or someone else should comment on that. Bob

The 40 character length of the dbr_string_t type that CA uses causes that 
limitation.

As to modifying the length of the CALC/OCAL fields of a calc or calcout 
record, if you do that make sure that you also modify the corresponding 
RPCL/ORPC fields to match, or when an expression longer than 40 characters 
gets coverted to postfix tokens it could overwrite memory belonging to some 
other field or record.  In recent versions of Base the size needed is 
calculated by the macro INFIX_TO_POSTFIX_SIZE() so all you have to give it is 
the size of the infix string.

- Andrew

> -----Original Message-----
> From: [email protected] on behalf of Ilya V. Kitaev
> Sent: Fri 12/5/2008 3:29 AM
> To: Kalantari Babak
> Cc: [email protected]
> Subject: Re: How to implement simple control algorithm (one more question)
>
> Hi,
> Thank you for your answer.
> I'd like to ask one more question:
> Is it ok to break 40 chars limit in CALC field( or another text fields
> like DESC) ?
> I've changed this limit  to 200 in calcoutRecord.dbd, db_access.c and
> epicsTypes.h (MAX_STRING_SIZE define) and it works ok.
>
> 2008/12/3, Kalantari Babak <[email protected]>:
> > Hi,
> >
> > You do not need to write your own CA application for that.
> >
> > Monitor alarm status of your "ai" with a "calcout" record and write to
> > your "bo" upon occurrence of the conditions.
> > This can be done for example as the following:
> >
> > record(calcout, "$(ALGORITHM)")
> > {
> >         field(INPA,"$(YOUR_AI_REC).STAT CP") # monitoring
> >         field(INPB,"$(YOUR_BO_REC).VAL NPP")
> >         field(CALC, "A=3?1:A=5?0:B")
> >         field(OOPT, "On Change")
> >         field(OUT,"$(YOUR_BO_REC) PP")
> > }
> >
> > Alarm status value for HIHI is 3 and for LOLO is 5.
> >
> > HTH,
> > Babak



-- 
The best FOSS code is written to be read by other humans -- Harold Welte
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