Experimental Physics and
Industrial Control System

"Tang, Johnny Y." <[email protected]> · Mon, 12 Apr 2004 13:11:26 -0400

JLAB's implementation of mbbiDirect and mbboDirect records were bidiretional.

________________________________

From: [email protected] on behalf of Purcell, J. David
Sent: Mon 4/12/2004 12:17 PM
To: Lionberger, Carl A.; Thompson, David H.; Andrew Johnson; tech-talk
Subject: RE: Bidirectional device support

To clarify the LabView implementation as SNS, although deployed via
shared memory, control of the remote/local switch for the LabView
devices is set up as Carl points out.  The switch is implemented in
LabView and only read with EPICS.  Control can not be taken away from
the poor guy testing (probably me).  So operators can not take control
of a diagnostic until it is returned to a remote controlled state.
However, work done locally must be reflected on operator screens and
although Dave Thompson does not have control over how we operate, he has
certainly helped us with shared memory and the "reflection" of settings
allowing us to operate.  I should also say that, obviously, all work
done locally is coordinated with operations.  

Dave

-----Original Message-----
From: Carl Lionberger [mailto:[email protected]]
Sent: Monday, April 12, 2004 10:57 AM
To: Thompson, David H.; Andrew Johnson; tech-talk
Subject: RE: Bidirectional device support

I think the desire for bidirectional records reflects some personal
preference; some people think there is some kind of elegance about it.
I
agree with Andrew that it is not realistic.  I think it can be easily
avoided
in all cases, as I outline below.

>===== Original Message From "Thompson, David H." <[email protected]>
>===== If you are trying to do I/O on the same point you are right.  You

>can't really turn most hardware around like that anyway.  There are two

>or three cases that I think we (at SNS) need to be able to do
>bi-directional I/O; when talking to a smart device and you want to do
>bumpless transfer of control between local and remote,

This sounds equivalent to having a remote/local switch on the device;
the
switch is implemented in labview.  I thought it was SNS policy to not
have
EPICS control remote/local switches.  These should be controlled at the
device
(locally).  EPICS reads them.  Some poor guy locally testing the
hardware
should not have control taken away from the control room.  Its not safe.

[>]when you have a
>device that can set one state and depends on Epics to set the other
>state,

For this you have an output record that sets it and a readback record
that
reads it.  I find the least confusing way to do this is to have the
output
record be momentary, ie, a bo with a HIGH of about 1 so that when you
push the
button it sets the state (which is read out) and returns to standby.

[>]and when you have more than one PV pointing at the same hardware
>address in the OUT field.

In this case, last gets it. This just says you monitor the val field.
The
difference from the normal case is that all device supports which write
to the
same hardware must post monitors when any of them controls it.  Its not
really
bidirectional control.

Carl

Carl Lionberger
SNS Controls Group
(865) 574-7636

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System