Experimental Physics and
Industrial Control System

Kevin Peterson via Tech-talk <tech-talk at aps.anl.gov> · Fri, 7 Jan 2022 14:15:36 -0600

Pete,

Which version of the motor record is being used? I've seen unexpected

motion problems with ancient versions of the motor record, but they

involved stopping a motor while it was in SET mode, not restoring

autosaved positions.

A new motor-record field, RSTM, is available in the master branch of the

motor module, which gives users more control over how autosaved

positions are restored:

  https://github.com/epics-modules/motor/pull/160

Kevin

On 1/6/22 15:13, Siddons, David via Tech-talk wrote:

I would like to suggest an addition to the motor record logic (or

save-restore, not sure which). I have been bitten several times by

having a set of motors under save-restore and having a restart provoke a

runaway. The sequence goes like this:

motor system running fine, save-restore operating.
IOC is stopped.
Motors are powered down.

motors powered up, causing their internal position registers to be set

to zero.

IOC re-started, save restore writes previous positions into motor

driver, causing them to move to that position, and havoc!

My proposed change would cause someone (motor, save-restore) to notice

that the hardware and software disagree, and ask the User how they want

to resolve this dilemma. Those of you old enough to remember Spec know

that this is exactly how Spec behaved on startup. If the User decides

that the software is right, then the new positions should be entered in

the SET=1 mode. If she decides that the hardware is right, then that

value should be entered in the same way. It isn't enough to just take

the hardware value as right, since it is quite liable to be wrong, as

described above, although that would prevent runaways.

In my case, the problem was compounded by the fact that the STOP command

did not work! But that is the subject of another discussion.

Pete.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System