Experimental Physics and
Industrial Control System

Zenon Szalata <[email protected]> · Tue, 6 Aug 2013 10:29:59 -0700

Thank you for your suggestion.  I will pursue this.
Zen

On 08/06/13 10:06, Andrew Johnson wrote:

Hi Zen,

On 08/06/2013 11:47 AM, Zenon Szalata wrote:

I ran the same IOC on two different computers which have access to the
same "public restricted" sub-net where the Beckhoff is connected.  In
both cases the computers are more powerful and IO fails sometimes very
often at other time not so often.  "public restricted" is a sub-net
configured such that it is only accessible from two public sub-nets here
at SLAC.  Other than that, it is supposed to be a normal sub-net.

When the IOC fails to do IO, it is the read in the write-read that
fails.  As best as I can tell, the read fails immediately after the
write completes.  This is based on observing the print statements in
both the write and read routines, which makes rather subjective.

The error printed is:

2013/08/05 08:55:14.982 modbusAsyn::doModbusIO port BKH15 error
calling writeRead, error=sioc-esb-bkh15:502 timeout: Resource
temporarily unavailable, nwrite=6/6, nread=0

Is it some kind of networking issue?

That error message does suggest so.  I would suspect that when the
Beckhoff is on your "public restricted" subnet it may be getting swamped
by broadcast packets from other devices on that network, all of which
have to be examined and thrown away by the network stack.  If the device
doesn't have very much CPU power this could easily explain the problem;
ask your network guys for the statistics on the volume of traffic being
fed to it.  Do you have any other similar "public restricted" subnets
you could move it into to see whether the same effect occurs there?

- Andrew

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System