Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Fri, 9 Jan 2009 10:28:32 -0600

Hi Ralph,

On Friday 09 January 2009 03:55:19 Ralph Lange wrote:
>
> sorry for being smartass without looking at the code - I'm still on
> vacation, at home, without a full-size computer that would be able to
> run a reasonable editor or EPICS. The EPICS/CA code just doesn't fit
> onto my PDA screen....

No problem, sorry if I came across a little rudely.

> Does that mean that the CA client doesn't do anything special and doing
> a "caget XXX.RTYP" issues a value DBR type request?

Correct, attributes look just like a read-only DBF_STRING field to CA clients 
or when read through a DBF_INLINK:

epics> dbpf anjHost:sin.INP anjHost:sin.RTYP
DBR_STRING:          "anjHost:sin.RTYP NPP NMS"
epics> dbpf anjHost:sin.PROC 1
DBR_UCHAR:          1         0x1
epics> dbgf anjHost:sin
DBR_STRING:          "stringin"

> Ernest: Why do you see a DBR_CLASS_NAME request at the Gateway, then?

If you use the "PV Info" menu item on MEDM, it does a ca_get() using 
DBR_CLASS_NAME to display the record type in the resulting dialog box.

I think the original idea was that CA client programs should regard PV names 
as black boxes and not try and replace the field name part in one, so the 
record type was made available by adding the DBR_CLASS_NAME data type and 
that's what MEDM used.  In practice though someone wanted to be able to use 
the regular caget as DBF_STRING for this, so attributes and RTYP were added.

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

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System