Experimental Physics and
Industrial Control System

Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov> · Fri, 5 May 2023 07:40:01 -0700

On 5/3/23 20:35, Dmitry Yu. Bolkhovityanov wrote:

Michael,

On Wed, 3 May 2023, Michael Davidsaver via Tech-talk wrote:

https://github.com/mdavidsaver/pvxs/blob/master/documentation/netconfig.rst

Thanks for a concise description of possible addressing methods!

I have a question related to addressing: the "pvAccess Protocol Specification" -- e.g. https://epics-controls.org/wp-content/uploads/2018/10/pvAccess-Protocol-Specification.pdf -- contains the following statement:

     A  client  API  MAY  also  allow  a  user-specified  server
     address;  in this case, the searching process would be bypassed
     and the specified server address data used directly.

The question is: does PVXS allow specifying a server address on a per-PV basis, e.g. "(SERVER_ADDRESS_SPEC)PV_NAME"?  Or does the "user-specified server address" in the statement above mean "address specified via EPICS_PVA_ADDR_LIST" only?

This has been possible since PVXS 0.2.0, although I notice that it isn't yet mentioned in the documentation.
The client *Builder objects have a server() method which takes a hostname/IP address.

https://github.com/mdavidsaver/pvxs/blob/dd2f076b4aa6dc63fb91980eda711eabee910696/src/pvxs/client.h#L685

An example usage in the pvxlist executable.

https://github.com/mdavidsaver/pvxs/blob/dd2f076b4aa6dc63fb91980eda711eabee910696/tools/list.cpp#L162

Also, it may not be relevant for you, but do be aware that some servers based on pvAccessCPP have a bug
whereby PV names must be searched for by some client before any client can create a channel.

In general, I'm not sure I would recommend bypassing the search phase as a regular operation.  Depending
on your use case you might prefer search over TCP (set $EPICS_PVA_NAME_SERVERS).

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System