Experimental Physics and
Industrial Control System

Carl Lionberger <[email protected]> · Tue, 13 Apr 2004 10:24:25 -0400

This can be solved by device support much like the case of two device
supports writing to the same hardware,-- each has to post monitors when
the other changes the setting.  So this device support has to post
monitors whenever the hardware setting is changed by labview and the
device is in local.  Also it has to post monitors with the unchanged
value when anyone tries to set it using epics while in local mode, so
the operator screens will recoil.  Because such attempts amount to a
caput, the device support has to put back the hardware setpoint into val
and post monitors if in local mode, and set the hardware and post
monitors if in remote mode. Although this can be viewed as losing the
operator settings if they are input while in local mode, it is after all
invalid to enter settings remotely while in local mode.  Without the
remote/local switch, the difficulties Andrew described are unavoidable.

Carl

On Mon, 2004-04-12 at 12:17, Purcell, J. David wrote:
> 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
> 
-- 
Carl Lionberger
SNS Control Systems Group, ORNL
Phone: 865-591-9951
Fax:   865-241-6739

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System