Experimental Physics and
Industrial Control System

"Mooney, Tim M." <[email protected]> · Thu, 4 Jun 2015 13:36:10 +0000

Kevin wrote:

> Another reason I've wanted to enhance the motor record is that I've
> found it to be the obstacle when trying to implement multi-axis
> coordinate transforms of arbitrary motor axes using motors with
> soft-channel device support in such a way that all the target positions
> stay synchronized.  I can elaborate on that if falls within the scope of
> this discussion.

I may have solved part of this.  The MLLH and MLLV databases in optics are written so that
all virtual motors understand that they are part of a move started by any virtual motor,
so they do the right thing when they notice that hard motors have moved.

Tim Mooney ([email protected]) (630)252-5417
Software Services Group (www.aps.anl.gov)
Advanced Photon Source, Argonne National Lab

________________________________________
From: Kevin Peterson [[email protected]]
Sent: Tuesday, June 02, 2015 8:49 AM
To: Mooney, Tim M.; Rivers, Mark L.; [email protected]; EPICS Tech-Talk
Subject: Re: Draft requirements document for enhanced EPICS motor support

On 5/26/15 11:28 AM, Mooney, Tim M. wrote:
> I started to edit the requirements document, but the premise seems
> to be that we would like to get rid of the motor record if only we
> could.  I don't feel this way.  I think it's a very valuable
> implementation of the behavior needed for nearly all the motors on
> APS beamlines.  An important but small number of motors need a
> better model to do complicated motions, and I'd like to focus my
> effort on those needs, without also pursuing the goal of
> reimplementing stuff that works.

One of the reasons I have thought about rewriting or replacing the motor
record in the past is that the motor record was not designed to handle
multiple fields changing simultaneously.  Here is an example:

1. Change a motor's VAL field using an NPP link from another record in
the IOC
2. Set the motor's STOP field to one using an NPP link from another
record in the IOC
3. Process the record once by writing 1 to the PROC field; the motor
record sends the stop command to the controller and resets the STOP field.
4. Process the record a second time; this moves the motor to the VAL
specified in step #1.

Note: The behavior is the same when PP links are used to write to a
motor record that is disabled (DISA=DISV,DISP=1).

This failure to handle multiple field changes has resulted in motors
moving when users were trying to redefine a motor's position.

Another reason I've wanted to enhance the motor record is that I've
found it to be the obstacle when trying to implement multi-axis
coordinate transforms of arbitrary motor axes using motors with
soft-channel device support in such a way that all the target positions
stay synchronized.  I can elaborate on that if falls within the scope of
this discussion.

Kevin

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System