Re: read RVB and VAL don't match when moving smarAct motors without encoders

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

Juliane,

Having an open-loop move command is helpful, though I don't know how to 
map steps + frequency to EGU, but not sufficient to make open-loop axes 
work well with the motor driver.  The motor record expects a feedback 
position to be updated by the driver.

It would be fairly easy to write streamDevice support to allow sending 
the open-loop move command from EPICS.  I don't know how well this would 
work if some of the axes on the MCS controller needed open-loop moves 
and others work correctly with the EPICS motor driver.

Kevin

On 11/13/20 4:03 PM, Juliane Reinhardt wrote:
> Hi Kevin,
>
> we found the ASCII command to move a motor that does not have an encoder
> in the SmarAct manual, p70:
>
> Example:
> MST0,100,4095,100
> Performs 100 steps at full amplitude and 100 Hz on channel 0.
>
> Is that information enough to implement that in the MCS driver for
> EPICS? Would you be able to modify the driver or can you assist me in
> doing that? I have not experience yet in writing the actual EPICS
> drivers. I assume, we would add this option to the move command
> beginning in line 502 of the current smarActMCSMotorDriver.cpp
>
> Another naive idea would be to move the motor using the hardware's
> step-count register? I tried moving using caput $motor.RVAL but that
> doesn't work either. Any options to setup an RDBL Link to read positions
> from or does that only over complicate things and we should rather have
> the driver adapted?
>
> Thanks for your help,
> Juliane