Experimental Physics and
Industrial Control System

"Thompson, David H." <[email protected]> · Wed, 12 Nov 2008 09:51:03 -0500

If you are talking about doing it over the network connection I have
used used UDP packets before in some robotics applications. I built the
app using sun RPC which is UDP based.  You do have a packet size limit,
you have to be able to tolerate dropped packets, and if vxWorks it still
has to go through tNetTask in-bound.  With TCP it becomes a byte stream
and the OS is free to pack things any way it wants so you have no
control over timing, as compared with little control with UDP.  Getting
200 Hz depends on how much network you have to go through.  We once
teleoperated a robot over a link from Sandia Labs NM to Oak Ridge, not
at 200 Hz obviously.

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Ralph Lange
Sent: Wednesday, November 12, 2008 9:20 AM
To: EPICS Tech Talk
Subject: Fast Cross-IOC Loops?

Hello!

What would be the smartest way to implement fast cross-IOC loops that
are high-priority?

Problem: The CA server tasks on the target IOC are low priority (for
good reasons, I know!), so that - even with a fast synchronous device
support - any stupid slow-and-low record processing on that IOC will
introduce delays, which leads to jitter or multiple CA updates before
the target record gets processed.

Oh, yes: "fast" would be something below 200Hz.

Any hints welcome...
Ralph

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System