Experimental Physics and
Industrial Control System

Ron Sluiter <[email protected]> · Wed, 13 Aug 2008 11:43:29 -0500

Hello Matthew,
The ATHM logic needs a slight change to conform to the documentation.
The documentation for ATHM field says,

The state of the hardware's "home" switch. If 1, the motor has hit the
switch.

whereas the code is a bit more complicated. The ATHM fields is set by
either

the RA_HOME or the EA_HOME bit in the MSTA field based on the state of

the "Use Encoder If Present" (UEIP) field and the "Encoder present"
indicator

in the MSTA field.

    /* Get state of motor's or encoder's home switch. */
    if (msta.Bits.EA_PRESENT && pmr->ueip)
        pmr->athm = (msta.Bits.EA_HOME) ? 1 : 0;
    else
        pmr->athm = (msta.Bits.RA_HOME) ? 1 : 0;

The result of this is that the ATHM can either reflect the state of the
home limit switch (RA_HOME) or that the motor is at the encoder
determined home position (EA_HOME).
I took a quick survey of the motor record device drivers and only the OMS
drivers are setting EA_HOME.  I doubt if any one is using this so I plan
on changing the above logic to match the documentation; i.e., the ATHM
field will only reflect the state of the home limit switch.
The EA_HOME bit of the MSTA field should be set by device drivers
when the motor has an established home position and the motor is at
that position.
Ron

Pearson, MR (Matthew) wrote:

Hi,
At Diamond we're currently using several motor controllers, including
the OMS (58 and MAXv), the Delta Tau PMAC (PMAC2-VME, Geobrick) and the
Newport XPS.
The motor record has a field called ATHM, which is set to 1 when the
motor has hit a home switch.
The OMS and Newport drivers use this field correctly, in that ATHM is
set to 1 when the motor is at home position (and is 0 otherwise).
However, the PMAC driver retains the ATHM status when moving away from
the home position - it actually means 'homed' for this driver, rather
than 'at home'.
Most of the motor control at Diamond is performed using the PMAC driver,
so everyone here has become used to this convention. It is arguably more
useful to have a 'homed' status, rather than 'at home'. Especially since
the 'at home' status can be inferred from the position (once it is homed
of course).
Is it the case that every other driver apart from the PMAC driver obeys
the ATHM status? I was considering changing the XPS driver to bring it
in line with the PMAC driver (for the benefit of our beamline users
mainly). However, if every other motor controller driver out there obeys
ATHM, then changing another one to do something different probably isn't
ideal. In this case, we'll probably just leave it as it is.
Any thoughts on this? Or info on other motor controller drivers?
Regards,
Matthew
Dr Matthew Pearson

Software Systems Engineer

Diamond Light Source Ltd

Diamond House

Chilton, Didcot

OX11 0DE

Tel: +44 (0)1235 778538

(58

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System