Experimental Physics and
Industrial Control System

Ben Franksen via Tech-talk <tech-talk at aps.anl.gov> · Wed, 14 Apr 2021 16:35:01 +0200

Am 13.04.21 um 19:44 schrieb Ru Igarashi via Tech-talk:
> I have at least one problem with running EPICS CA Gateway 2.1.2
> on Scientific Linux/Redhat Enterprise Linux 7 with EPICS 3.14.12.4.
> For IOC's running EPICS 7 on CentOS 8 and clients on older OS and
> EPICS 3.14.12, the readback value for asynchronous 'caput' commands
> (caput -c) are often the old value, not new value.  I have an older
> gateway running on old hardware, OS and EPICS which also does this
> but 100 times LESS frequently for the same type of IOC and client.

I'd find it interesting to know the versions of these "older" products
where the problem seems to be (a lot) less severe.

> Further, when I see these errors, packet captures show the only
> differences in behaviour are that:
> - on the client side of the gateway, in the bad transaction, the
> "update" packet that follows the "write" arrives after the write
> is acknowledged whereas normal transactions have the
> acknowledgement packet arrive after the "update" packet.
> - on the server side of the gateway, in the bad transaction, the
> "update" packet carries a data payload of zeros in all bytes,
> whereas normal transactions have non-zero data payloads.

This sounds very much like a bug in either the ca-gateway or the PCAS
(in base). I agree with Ralph that implementing asynch caput correctly
in the ca-gateway is a difficult thing (and thus it is unlikely that it
will be fixed any time soon). I also agree with Ralph that you should
build the ca-gateway against at least base-3.15.8: there have been many
bugfixes in the CA client and the PCAS since 3.14.

Cheers
Ben
-- 
I would rather have questions that cannot be answered, than answers that
cannot be questioned.  -- Richard Feynman

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System