Experimental Physics and
Industrial Control System

Kevin Peterson via Tech-talk <tech-talk at aps.anl.gov> · Thu, 9 Jun 2022 10:30:55 -0500

Ray,

You can work around the initialization problem by adding a calcout

record to mirror the underlying motor's RBV:

record(calcout,"$(VM):rbvCalc")
{
    field(DESC,"Mirror RBV")
    field(CALC,"A")
    field(INPA,"$(M1).RBV CP MS")
}

And then using the calcout in the virtual motor's RDBL field:

  field(RDBL, "$(VM):rbvCalc")

Kevin

On 6/9/22 09:13, Gregory, Ray via Tech-talk wrote:

Hi,

I am developing a Soft Channel motor to be a virtual motor that controls

two other motors. The virtual motor is essentially a copy of one of the

underlying motors and applies ‘adjustment’ moves to the other motor it

controls in accordance with a pre-specified alignment profile (using a

simple linear equation determined by calibration).

Most of this is working well. However, when the IOC starts, the virtual

motor often fails to retrieve its RBV value from the underling motor.

I’ve included the soft channel motor record below.

How do I fix this?

I am using EPICS base version 3.14.12.6. I am currently developing on my

VM with Simulated motors. I’m not sure what differences to expect when I

deploy this to an actual instrument.

So far I haven’t found a simple solution.

However, I have created horribly complicated solution that seems to

work: I created another do-nothing Soft Channel motor and make it part

of the virtual motor system, so now the overall virtual motor controls 3

motors, one of them being the do-nothing motor. Then, if the RBV value

was not set properly at launch time, I move this do-nothing motor. This

has the effect of sometimes properly setting the RBV of the main virtual

motor. If that doesn’t work, I try it again, and again, up to some

maximum number. I call this process ‘kicking’ the RBV.

It's a kludgy and nasty solution. I would very much appreciate knowing

how to fix this in some simple way.

Thank you,

Ray Gregory

Oak Ridge National Laboratory

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System