Experimental Physics and
Industrial Control System

Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov> · Wed, 19 Jul 2023 09:30:29 -0700

On 7/19/23 08:30, Srinivas, Dhruv via Tech-talk wrote:

I was looking at PV structures and how to utilize them properly, and I’ve discovered that there are two ways to create them. The first is using  QSRV through .db files, and the other is using PVXS through C++ files. I was wondering what the differences between the two were in terms of functionality. From my rather limited experience with epics, the difference between the two seems like

QSRV is limited to built-in epics records, so wouldn’t be able to store a matrix of some kind.

This is the basic concept.  Although the idea of Group PV gives
more flexibility to compose complex Structures where the individual
members are mapped to record fields.  So one Group PV Structure can
map to storage in many records.

Two examples composing NTTable and NTNDArray.

NTNDArray example is more complex, but may be more relevant to you.  In it the
2D pixel array is stored in a 1D waveformRecord, while the width+height) are
stored in two longoutRecords.

https://github.com/epics-base/pva2pva/blob/master/iocBoot/iocimagedemo/table.db

https://github.com/epics-base/pva2pva/blob/master/iocBoot/iocimagedemo/image.db

https://mdavidsaver.github.io/pvxs/ioc.html#group-pv

https://epics-base.github.io/pva2pva/qsrv_page.html#qsrv_group_def

I am linking documentation for both pva2pva (aka. QSRV 1) and PVXS (aka. QSRV 2)
as the info() tag syntax for composing groups is the same.  If however, you
opt for c++ code the two APIs are different, and I would recommend PVXS alone.

However, I’m not sure if that’s actually the case. As such, I was hoping someone with more experience with PV structures could help explain the difference to me.

Sincerely,

Dhruv Srinivas

srinivas1 at llnl.gov <mailto:srinivas1 at llnl.gov>

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System