Re: Understanding Asyn-based motor controller driver

[Mark Rivers via Tech-talk <tech-talk at aps.anl.gov>]

Hi Abdalla,

1.       motor jogging: since the class does not implement the “::moveVelocity” function, does this mean that the driver does not support jogging at all? Or it does at the low-level motor record interface?

Yes, that is correct, the driver does not support jogging because it does not implement those methods.

VELO and ACCL fields: The class uses different variables to hold acceleration and velocity information other than the base class’s variables “motorVelocity_” and “motorAccel_”. Does this mean that VELO and ACCL fields are useless? Same thing goes for the OFF field.

That is not correct.  The motorVelocity_ and motorAccel_ fields in asynMotorController.h do not hold the velocity and acceleration information.  Those are "parameter numbers" used to identify that those values in the asynPortDriver parameter library.  They are used in calls like this in asynMotorController.cpp

https://github.com/epics-modules/motor/blob/34474ed958838ea5083f598fa4bd9f1ca7e1821c/motorApp/MotorSrc/asynMotorController.cpp#L297

This is the motorAcsMotion axis move() function:

https://github.com/epics-motor/motorAcsMotion/blob/2cfc752ccc82cb5143b41f1049076dc4b480cd46/acsMotionApp/src/SPiiPlusDriver.cpp#L769

It uses the "maxVelocity" and "acceleration" values passed to it from the motor record VELO and ACCL fields.

Another example, Automation1 driver in order to calculate the position, it reads the resolution from the controller it does not read motorResolution_ nor motorRecResolution_.

Again, motorResolution_ and motorRecResolution_ are parameter number, not values.  I just did a search and no drivers appear to use motorResolution_ at all.  The position values passed to the driver from the motor record are in "steps", i.e. although they are "double" values they are actually always integers with no fractional part.  For motor controllers that work in steps this is simple.  For controllers that use engineering units and not steps there is a translation required.  It is often implemented using the MRES field in the driver to generate a large integer value to be passed to the driver, which then divides by some number to get back to engineering units.  If the driver number is the same as MRES then the motor record units are the same as the controller units.  That is not required, they could be different, so the controller could be using mm and the motor record using microns, for example.

In general the driver does not need to know the motor record resolution, but in some unusual cases it does.  In that case the motorRecResolution_ parameter is used to communicate that information.  One case where it is used is for multi-axis coordinated motion (profile moves) on the Newport XPS controller.  The profile move API uses the user coordinate system in the motor record.  The driver thus needs to know the motor record resolution, direction, and offset to convert from user coordinates to controller coordinates.  That is what the motorRecResolution_, motorRecDirection_, and motorRecOffset_ fields are used for.

Mark

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From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Abdalla Ahmad via Tech-talk <tech-talk at aps.anl.gov>
Sent: Monday, January 9, 2023 4:42 AM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: Understanding Asyn-based motor controller driver

 

Hi

 

I am trying to understand how a motor controller driver works and how the asynMotorController and Axis classes map to the EPICS motor record. For example, I am investigating this driver from ACS motion https://github.com/epics-motor/motorAcsMotion to see if it supports some functions from the motor record that are required by our data acquisition system. Here are my questions:

1.       motor jogging: since the class does not implement the “::moveVelocity” function, does this mean that the driver does not support jogging at all? Or it does at the low-level motor record interface?

2.       VELO and ACCL fields: The class uses different variables to hold acceleration and velocity information other than the base class’s variables “motorVelocity_” and “motorAccel_”. Does this mean that VELO and ACCL fields are useless? Same thing goes for the OFF field.

 

In other words, if a motor driver is based on the motor record, does this guarantee that all fields are functional and working with the controller? How to verify if a certain function not implemented in the asyn classes but working and implemented somewhere else?

 

Best Regards,

 

Abdalla Al-Dalleh

Control Engineer

SESAME (Synchrotron-light for Experimental Science and Applications in the Middle East)
P.O. Box 7, Allan 19252, Jordan
Tel: +96253511348 , ext. 265

Fax: +96253511423

abdalla.ahmad at sesame.org.jo

www.sesame.org.jo