Experimental Physics and
Industrial Control System

"Mark Rivers" <[email protected]> · Tue, 5 Jan 2010 12:57:58 -0600

It would be nice if CAJ could use the environment variables, in addition
to the jca.properties file and command line definitions.

But the more serious problem is that I've been told it is (was?)
difficult in Java to discover the broadcast address of all network
interfaces, so it does not use those as the default, it uses
255.255.255.255 instead.

Mark

-----Original Message-----
From: Dirk Zimoch [mailto:[email protected]] 
Sent: Tuesday, January 05, 2010 8:08 AM
To: Mark Rivers
Cc: [email protected]
Subject: Re: CAJ or PV gateway problem?

Mark Rivers wrote:
> Folks,
>  
> We found a problem with CAJ and the PV gateway yesterday.  The problem
is that CAJ "out of the box" (e.g. without changing any of the default
properties) will connect fine to PVs on the local subnet if they are
contained in a VME IOC or soft IOC.  But CAJ will not connect to PVs
that are present in a PV gateway on the local subnet.
>  
> We've figured out the problem, and it is easy to reproduce even with
traditional CA from EPICS base.  The problem is that CAJ defaults to a
broadcast address of 255.255.255.255 when searching for PVs.  VME IOCs
and soft IOCs respond to such a broadcast, but the PV gateway does not.
>  

Hi Mark,

The EPICS default, according to the CA Reference Manual, is to use the 
broadcast addresses of all network interfaces. (If this makes sense or 
not is another issue -- imagine an IOC and a CA client on the same 
computer with two network interfaces => duplicate channels.)
This behavior can be modified with the environment variables 
EPICS_CA_ADDR_LIST and EPICS_CA_AUTO_ADDR_LIST.

The CA gateway parses its command line parameters for server and client 
address and modifies the environment variables before starting the CA 
server part. Normally, one specifies the broadcast address of one 
network card as the server address. Thus, I would say the gateway is 
working correctly.

If CAJ uses an other default and/or does not look at the environment 
variables, CAJ does not conform to the CA Reference Manual. I dare to 
say it is buggy. (And don't tell me "Java cannot read the environment" 
-- all Java fans say "Java can everything" :-P )

I wonder why you get any reply at all using 255.255.255.255? Is there 
any "magic" in the IOC server that allows IOCs to respond to 
255.255.255.255 and that is not included in the portable CA server?

Dirk

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System