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<== Date ==> <== Thread ==>

Subject: Re: RTYP field through the PV Gateway
From: Ralph Lange <Ralph.Lange@bessy.de>
To: Andrew Johnson <anj@aps.anl.gov>
Cc: EPICS Core Talk <core-talk@aps.anl.gov>
Date: Fri, 09 Jan 2009 10:55:19 +0100
Hi Andrew,

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....

Good to hear that RTYP is a database attribute and the .VAL extension is implemented in the database. Does that mean that the CA client doesn't do anything special and doing a "caget XXX.RTYP" issues a value DBR type request?

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

Cheers,
Ralph


Andrew Johnson wrote:
Hi Ralph,

On Thursday 08 January 2009 07:56:53 Ralph Lange wrote:
RTYP is a pseudo field: When a read request for a "*.RTYP" PV comes in,
the CA client library  strips the ".RTYP" and converts it to a
DBR_CLASS_NAME request.

Wrong, RTYP is one of two standard Record Attributes, pseudo-fields supported by the database whose values are specific to the record type and can be set (and new attributes created) using dbPutAttribute(). If the .RTYP handling was an artifact of CA like you suggest I wouldn't be able to do this from the ioc shell:

epics> dbgf mrk:stringinsyn.RTYP
DBR_STRING:          "stringin"

Go read section 6.14 of the AppDevGuide. Attributes have been part of the IOC since at least R3.13.0, just nobody uses them much...

The only other case of CA-EPICSdb dependency (that I know of) is adding
the ".VAL" extensionsto PVs without a field name. I don't know if this
is done by the client or the server right now - it should be done on the
server side for the same reasons.

Nothing explicitly adds .VAL to the PV name; when someone [currently RSRV, by calling db_name_to_addr()] presents a PV name to dbNameToAddr() if the name doesn't contain a field part it looks up the "VAL" field automatically. Thus this is already done in the server.

- Andrew

Replies:
Re: RTYP field through the PV Gateway Ernest L. Williams Jr.
Re: RTYP field through the PV Gateway Andrew Johnson
References:
Re: RTYP field through the PV Gateway Ralph Lange
Re: RTYP field through the PV Gateway Andrew Johnson

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