Experimental Physics and
Industrial Control System

Dirk Zimoch <[email protected]> · Tue, 05 Jan 2010 15:08:00 +0100

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