Experimental Physics and
Industrial Control System

Hi, Mark.

Thanks for the reply.

Yeah, I was trying to avoid modifying the upstream MCA module, or
vendoring the MCA module into the IOC. I was hoping I could do the
EPICS equivalent of sub-classing the MCA module, but it sounds like
that is not possible.

As suggested, I made a separate ``20bmxmap4b:mca1_R0BH`` bi record. I
then created an ``ophyd.Component`` subclass that modifies the PV with
regular expressions [1], which I'm not thrilled about but I believe
I'm in a lesser-of-two-evils situation here.

Cheers,
Mark

[1] https://github.com/spc-group/haven/blob/45fef324bb3d293cf30008c713c82b8a3a19664f/haven/instrument/fluorescence_detector.py#L53

On Sun, Jun 18, 2023 at 03:07:27PM +0000, Mark Rivers wrote:
> Hi Mark,
>
> Since this new field is intended for use by a single CA client (Ophyd for Bluesky) I think it is a better idea to use additional records and modify Ophyd to handle them.  Then all changes can be external to the MCA module, and Bluesky does not need to depend on a new release of the MCA module.
>
> Note that your gitlab link is not accessible to those of us who are not APS employees.
>
> Mark
>
> ________________________________
> From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Wolfman, Mark via Tech-talk <tech-talk at aps.anl.gov>
> Sent: Monday, June 12, 2023 11:25 AM
> To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
> Cc: Delgado, Uriel <udelgado at anl.gov>
> Subject: add fields to an existing record
>
> Hi, tech-talkers.
>
> Apologies in advance if parts of this don't make sense, I'm not that familiar with EPICS yet.
>
> I'm hoping to add a new region-of-interest field [1] to the MCA records used in an existing IOC for our DXP fluorescence detector.
>
> Similar to the other ROI fields, I'd like to have ``20bmxmap4b:mca1.R0BH``.
>
> This will be a 'bi' field that doesn't do anything in the IOC, but is used by bluesky/ophyd during staging to determine whether the specific ROI is hinted in bluesky (hence BH for "bluesky hint") [2] and is included in the calculations for summing ROI's across elements. I've added extra records to an IOC before, and so I tried adding this as a record but EPICS complained because my record name included a '.' character.
>
> One solution is to add a record like "20bmxmap4b:mca1_R0BH", but this makes the Ophyd part more complicated since the Ophyd MCA support expects the ROI to have a ``.Rn`` prefix and then tries to append the ``BH`` on the end[3]. Adding a record like ``mca1_R0BH`` means I have to re-write the MCA support in ophyd so I'd prefer to use the ``mca1.RnBH`` PVs if I can.
>
> The full IOC is available on gitlab, though it's presently a work in progress.
>
> Looking forward to hearing any ideas on how to make this work.
>
> Thanks,
> Mark
>
> [1] https://epics-modules.github.io/mca/mcaRecord.html#Region-Of-Interest_Fields
> [2] https://blueskyproject.io/ophyd/user_v1/reference/signals.html#kind
> [3] https://github.com/bluesky/ophyd/blob/0802c77ec973b0ba9f8554d3bcf3a3001def7f66/ophyd/mca.py#L14
> [4] https://git.aps.anl.gov/20BM/20bmdxp/-/tree/main/

--
My work schedule may not be the same as your work schedule. Please
don't feel obligated to respond to this e-mail outside of your normal
work hours.

This message may be signed or encrypted with Pretty Good Privacy (PGP)
key BE1E3158.

https://keys.openpgp.org/vks/v1/by-fingerprint/BB98174E34193EDCEA0F423C457826FCBE1E3158