Experimental Physics and
Industrial Control System

Hi Rolf,

On 2013-06-14 you wrote:
> For DOL on output records, however, one could store the constant link
> value, which is evaluated on record init in a record private structure
> and pick it up from there when processing.
> Ideally this private value should be updated, if the value of the
> constant link is changed. Mhhh?

An output record could make the DOL field special(SPC_MOD) and redo the link 
initialization whenever it gets set to a constant.  It would require adding a 
new field to the record type to store the converted constant, and using that 
value instead of the previous VAL when OMSL is closed_loop.  The attached 
changes to the ao record type demonstrate this (but might not apply cleanly 
using patch as they're against the latest 3.15 branch).

This is still a behavior change though, so I couldn't put it into an official 
3.14 release.  I also don't think we can implement this solution everywhere; 
ao, bo, dfanout, longout, mbbo and mbboDirect might arguably be done by 
reasoning that they all have OMSL fields, but we're actually changing the 
behavior of the DOL field more than OMSL, and in 3.15 the seq record has 16 
of those.

I also just noticed that the ao's OIF == Incremental setting is ignored when 
DOL is a constant; that's not really consistent either (or documented).

I don't think I want to make the change this way though, I'd rather take out 
the special handling of const links from the record code as part of my link-
support changes, which should be more flexible and comprehensive.  It should 
be possible to store the converted value in the link data structure and only 
do the conversion when it gets changed, and I think the result will simplify 
the record support code as well.

- Andrew
-- 
It is difficult to get a man to understand something, when his salary
depends upon his not understanding it. -- Upton Sinclair

=== modified file 'src/std/rec/aoRecord.c'
--- src/std/rec/aoRecord.c	2012-12-10 15:25:58 +0000
+++ src/std/rec/aoRecord.c	2013-06-14 19:26:38 +0000
@@ -120,8 +120,10 @@ static long init_record(aoRecord *prec, 
     }
     /* get the initial value if dol is a constant*/
     if (prec->dol.type == CONSTANT) {
-	if(recGblInitConstantLink(&prec->dol,DBF_DOUBLE,&prec->val))
-	    prec->udf = isnan(prec->val);
+        if (recGblInitConstantLink(&prec->dol, DBF_DOUBLE, &value)) {
+            prec->val = prec->docv = value;
+            prec->udf = isnan(value);
+        }
     }
 
     /* must have write_ao function defined */
@@ -189,8 +191,10 @@ static long process(aoRecord *prec)
 
 	/* fetch value and convert*/
 	if (prec->pact == FALSE) {
-                if ((prec->dol.type != CONSTANT)
-                && (prec->omsl == menuOmslclosed_loop)) {
+            if (prec->omsl == menuOmslclosed_loop) {
+                if (prec->dol.type == CONSTANT)
+                    value = prec->docv;
+                else
                     status = fetch_value(prec, &value);
                 }
                 else {
@@ -270,6 +274,12 @@ static long special(DBADDR *paddr, int a
 	    return (status);
 	}
 	return (0);
+    case SPC_MOD:
+        /* DOL changed */
+        if (after && prec->dol.type == CONSTANT) {
+            recGblInitConstantLink(&prec->dol, DBF_DOUBLE, &prec->docv);
+        }
+        return 0;
     default:
         recGblDbaddrError(S_db_badChoice,paddr,"ao: special");
         return(S_db_badChoice);

=== modified file 'src/std/rec/aoRecord.dbd'
--- src/std/rec/aoRecord.dbd	2002-07-12 21:35:43 +0000
+++ src/std/rec/aoRecord.dbd	2013-06-14 19:49:21 +0000
@@ -35,6 +35,7 @@ recordtype(ao) {
 	field(DOL,DBF_INLINK) {
 		prompt("Desired Output Loc")
 		promptgroup(GUI_OUTPUT)
+		special(SPC_MOD)
 		interest(1)
 	}
 	field(OMSL,DBF_MENU) {
@@ -205,6 +206,11 @@ recordtype(ao) {
 		prompt("Current Raw Value")
 		pp(TRUE)
 	}
+	field(DOCV,DBF_DOUBLE) {
+		prompt("Desired Output Const")
+		interest(3)
+		special(SPC_NOMOD)
+	}
 	field(ORAW,DBF_LONG) {
 		prompt("Previous Raw Value")
 		special(SPC_NOMOD)

Replies:

Re: analog output record - constant DOL Benjamin Franksen

References:

Re: analog output record - constant DOL Rolf Keitel

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