Re: How to reset encoder counts after controller power off

[Kevin Peterson via Tech-talk <tech-talk at aps.anl.gov>]

The DVAL is the position field that is usually autosaved.  The readback 
fields (RBV, DRBV, and RRBV) are not writable and cannot be restored by 
autosave.

The setPosition method of a model-3 motor driver is called when an 
autosaved position is restored.  The position argument should be the 
DVAL to be restored divided by the MRES, which should have units of steps.

What happens when the setPosition method sends the command to the 
controller to redefine the position is obviously controller-dependent. 
The RMP and REP fields are usually updated by queries of the theoretical 
(motor) and feedback (encoder) positions in the controller or axis poll 
methods.

Whether or not the motor record accepts the restored position depends on 
the RSTM field.  The "normal" motor record behavior is discard the 
restored position if the controllers position is sufficiently non-zero 
(>RDBD).  This results in setPosition not being called.

I don't know why the RMP/REP fields would change when setting using SET 
to redefine the VAL field, but not when VAL was restored by autosave.

I do have some questions, however:

1. What is the value of the FOFF field?  Does OFF remain constant when 
restarting the IOC?

2. Does the problem persist if the DVAL field is autosaved instead of 
the VAL field?

3. What is the output of the following command after the IOC is done 
booting:

  epics> dbpr "xxx:m1", 9

Kevin



On 7/13/23 08:41, 岳宗仰 via Tech-talk wrote:
> Hi, tech-talk,
>
> I have a motion controller, and write driver support for it by model 3.
>
>
> After power off, the pulse information and encoder counts of motor has 
> been lost, and we want to save this informations.
>
>
> The setPosition(double position) has been rewrote.（I think this method 
> is used for autosave）
>
> Through it, I can reset the pulse counts at any position.
>
> $caput xxx.m1.SET 1
>
> $caput xxx:m1.VAL 0
>
>
> So I use autosave module, and save the .RBV and .VAL PV.
>
> After IOC and controller restart, the .RBV and .VAL PV has been changed, 
> But .RMP, .REP PV not changed and the register of pulse counts of 
> controller also not change.
>
> Have you met this case?
>
> I would appreciated some suggestions.
>
>
> Zongyang yue
>
> Thanks