Experimental Physics and
Industrial Control System

Kevin Peterson via Tech-talk <tech-talk at aps.anl.gov> · Tue, 9 Nov 2021 11:41:52 -0600

Randall,

tl;dr The EPICS nPoint motor driver does not currently provide a way to

execute a user-specified wavetable.

I took a closer look at the driver. The controller's wavetable

functionality is used internally to implement trapezoidal motion

profiles for every point-to-point move.

Specifically, the move method does the following:

1. generates the trapezoidal move profile:

https://github.com/epics-motor/motorNPoint/blob/4d8b0d1cc0dc78315f8dad1279fd53a1e4cac0ce/nPointApp/src/LC400MotorDriver.cpp#L732

2. writes the trapezoidal move profile to the controller:

https://github.com/epics-motor/motorNPoint/blob/4d8b0d1cc0dc78315f8dad1279fd53a1e4cac0ce/nPointApp/src/LC400MotorDriver.cpp#L737-L738

4. runs the loaded waveform:

https://github.com/epics-motor/motorNPoint/blob/4d8b0d1cc0dc78315f8dad1279fd53a1e4cac0ce/nPointApp/src/LC400MotorDriver.cpp#L798

The wavetable records in LC400_auxParameters look like they are mostly

used as readbacks. I don't know how helpful the output wavetable

records are.

Asyn model-3 motor drivers like the NPoint LC400 driver can implement

profileMove methods which allow users to specify desired positions in an

EPICS waveform:

https://github.com/epics-modules/motor/blob/6d127cd6f433ff34256a53d6e7ff0309cc741dad/motorApp/Db/profileMoveAxis.template#L32-L42

The profileMove screens in the motor module look very similar to the

trajectoryScan screen here (trajectoryScan sequence programs pre-date

asyn model-3 motor drivers):

  https://epics-modules.github.io/motor/trajectoryScan.html#MEDM%20screens

Kevin

On 11/8/21 14:47, Randall Cayford wrote:

Thanks Kevin.

I’ve got those records but I’m not clear on what you mean.  None of those PVs appear to set a wavetable entry.  Are you saying that the current implementation only allows keeping the wavetable in the outside program and issuing a series of moves by setting the val motor field, waiting, and setting the next?  So not using the ability of the nPoint to do custom wavetables at all?  Is loading a custom wavetable what you mean by profileMove isn’t implemented?

Randall

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System