Re: Mapping customised pva structures to epics v4 Normative Types and v3 PVs (channel access).

[Gabriel Fedel via Tech-talk <tech-talk@aps.anl.gov>]

Hi Heinz,

On phoebus you can access specific fields from NT PVs using /, for example you could access the labels as:

TEST:LLPG/labels

As far I know phoebus still does not implement a way to edit the table itself (but it may exist an interest for it).Using a NTTable you could also use Save and Restore (we are using it here at ESS), but there is some limitations (e.g. not possible to change labels).

if you want to change only one column of the table, you could do something like this:

pvput TEST:LLPG "{'value' : {'Ch':[1,2]}}"

Cheers

Gabriel

---

From: Tech-talk on behalf of Heinz Junkes via Tech-talk
Sent: Thursday, August 14, 2025 4:25 PM
To: Anders Lindh Olsson
Cc: Mark Rivers via Tech-talk
Subject: Re: Mapping customised pva structures to epics v4 Normative Types and v3 PVs (channel access).

Hi,

I have now chosen NTTables instead of a custom structure in order to at least make ArchiverApplianc happy.

(p4ptest) epics@epics-spielwiese:~/FHI/TEST_PVA$ pvinfo TEST:LLPG
TEST:LLPG
Server: 10.0.0.40:5075
Type:
    epics:nt/NTTable:1.0
        string[] labels
        structure value
            ushort[] Ch
            ushort[] Width
            ushort[] Delay
            ushort[] ExtraDly
            ushort[] Atten
        string descriptor
        alarm_t alarm
            int severity
            int status
            string message
        time_t timeStamp
            long secondsPastEpoch
            int nanoseconds
            int userTag

(p4ptest) epics@epics-spielwiese:~/FHI/TEST_PVA$ pvget  TEST:LLPG
TEST:LLPG <undefined>
Ch Width Delay ExtraDly Atten
 1  1000   100       10     1
 2  2000   200       20     2

Unfortunately, I am unable to set individual values in the table using pvput. I can only address everything:

epics@epics-spielwiese:~/FHI/TEST_PVA$ pvput TEST:LLPG value.Ch="[3,4]" value.Width="[111, 222]" value.Delay="[11, 223]"  value.ExtraDly="[11, 22]"  value.Atten="[1331, 2232]”

Old : 2025-08-14 16:22:29.599
Ch Width Delay ExtraDly Atten
 3   111    11       11  1111
 4   222   223       22  2232
New : 2025-08-14 16:22:35.699
Ch Width Delay ExtraDly Atten
 3   111    11       11  1331
 4   222   223       22  2232

I also have no idea how I can then address the individual fields in Phoebus.

Heinz

> On 13. Aug 2025, at 11:24, Anders Lindh Olsson via Tech-talk <tech-talk@aps.anl.gov> wrote:
>
> Hello,
>  On your question:
> >> Now the question to the group: Is there a better way? And how would you implement my idea?
>  I would map the data structure of the system to EPICS rather than the other way around. So I would compose PVs like FHIFEL:llpg_1:Ch1-Width, FHIFEL-llpg_1:Ch1-Delay, etc.
>   Cheers
> Anders
>  On 2025-08-13, 07:27, "Tech-talk" <tech-talk-bounces@aps.anl.gov> wrote:
> Guten Morgen,
>  One thing that has been on my mind for a long time:
>  We have developed our own devices such as llrf generators, pulse generators, etc., which run on a Raspberry Pi or BeagleBone Black as a management interface.
> We then use p4p on that devices and offer the data points in a pva structure tailored to the respective device.
>  E.g.
>  (base) hactar:~ junkes$ pvinfo  FHIFEL:llpg_1
> FHIFEL:llpg_1
> Server: 141.14.134.173:5075
> Type:
>     structure
>         ushort Ch1_Width
>         ushort Ch2_Width
>         ushort Ch1_Delay
>         ushort Ch2_Delay
>         ushort Ch1_ExtraDly
>         ushort Ch2_ExtraDly
>         ushort Ch1_Atten
>         ushort Ch2_Atten
>   epics@felpvagate:~$ pvinfo FHIFEL:bbamp_1
> FHIFEL:bbamp_1
> Server: 10.0.0.110:5075
> Type:
>     structure
>         boolean ITLK
>         boolean TRIG
>         boolean PWR
>         boolean STAT
>         double SWR
>         double FWD
>         double REV
>         byte RFIN
>         double TSET
>         double TMEAS
>         int PIDI
>         int PIDV
>         boolean TTHI
>         boolean PIDLU
>         double PID_PWR
>         boolean CLRER
>  Now we are experiencing some issues with it.
>  1.) The ArchiverAppliance cannot archive these PVs.
> 2.) Our 'old' Save&Restore supports channel access only.
>  How should we best deal with this?
>  My current idea is to implement a service (Python?) that reads this user-defined structure with pva, breaks down the structure into individual NT-pvs and offers these 'individually' via pva (for the Archiver Appliance, for example) and, at the same time, also offers these PVs as ca-PVs for channel access (for our Save&Restore).
>  Now the question to the group: Is there a better way? And how would you implement my idea?
>  Danke Heinz
>  ------------------------------------------------------------------------------
> Fritz-Haber-Institut    | Phone:         (+49 30) 8413-4270
> Heinz Junkes             | Fax (G3+G4):   (+49 30) 8413-5900
> Faradayweg 4-6        | VC: https://zoom.fhi.berlin/junkes
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> All sort of things cropping up at the last moment. Uh, how are we for time?”
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