Re: PV Access

["Kivel Niko \(PSI\) via Tech-talk" <tech-talk at aps.anl.gov>]

Hi all

I double Ben's a remark about the deprecation. But, I'm not in the position to make such recommendations.

I never anticipated this matter to get out our hand like this 😊

To add even another layer of confusion, there is a Wiki entry that uses 'db:' and 'ca:' in the INP.

https://wiki-ext.aps.anl.gov/epics/index.php/JSON_Field_Values

Whether this is still valid or not, I don't know.

best

Niko

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Dr. Niko Kivel

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email: niko.kivel at psi.ch

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From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Ben Franksen via Tech-talk <tech-talk at aps.anl.gov>
Sent: Thursday, March 26, 2020 10:42
To: Ralph Lange; EPICS Tech Talk
Subject: Re: PV Access

 

Am 26.03.20 um 10:18 schrieb Ralph Lange via Tech-talk:
> The '{db:"record.VAL"}' definition appears in the *configuration* of the
> calc-Link.
>
> Every new link type (listed at the head of the referenced document) defines
> its own syntax for JSON configuration. The namespace for the keys in that
> configuration syntax is completely separate. The fact that the calc link
> understands a "db:" tag in its configuration does not mean that
> tag/functionality is available anywhere else, e.g. in the configuration of
> a different link type or at top level when configuring a field in a
> database record.

The documentation does not mention "db" as a valid JSON link type at
all. This keyword only appears in the example. At the same time, the
docs say:

args
A JSON list of up to 12 input arguments for the _expression_, which are
assigned to the inputs A, B, C, ... L. Each input argument may be either
a numeric literal or an embedded JSON link inside {} braces. [...]
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I guess the docs couldbe a bit clearer here. At least providing a
reference to where this "db" JSON link type is defined.

> All existing link types (DB/CA, numerical CONSTANT, hardware links from
> link.h) continue to work as before - otherwise introduction of the link
> support would have broken all existing applications and databases. (We're
> not *that* evil.)

A clean break would have been a possibility that I would hesitate to
call "evil", /if/ publicly anncounced and with a deprecation period. If
it had been deprecated in base-3.15, then I guess removing support for
such PV names in base-7.0 would be perfectly appropriate. The number of
affected users probably tends to zero anyway.

Just my 2 cents.

Cheers
Ben

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