Re: How to configure waveform record to read remote PV via PVAccess in EPICS

[Varuna Crishan Meddage via Tech-talk <tech-talk at aps.anl.gov>]

Thank you

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From: Michael Davidsaver <mdavidsaver at gmail.com>
Sent: Wednesday, March 25, 2026 2:28 PM
To: Varuna Crishan Meddage <vmeddage at fnal.gov>
Cc: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: Re: How to configure waveform record to read remote PV via PVAccess in EPICS

 

[EXTERNAL] – This message is from an external sender

On 3/25/26 12:13 PM, Varuna Crishan Meddage via Tech-talk wrote:

I am trying to create a waveform record in my IOC that takes its values from a remote PV hosted on another serverusing EPICS PVAccess (PVA).

Here’s what I want to achieve:

• Define a waveform record locally (e.g., LOCAL:WF)
• Subscribe to a remote PV (e.g., REMOTE:ARRAY:PV) on a server with a known IP address and port
• Automatically update the waveform at a set scan rate

Take a look at PVA links:

https ://epics-base.github.io/pvxs/pvalink.html

https ://github.com/epics-base/pvxs/blob/6f7942e4af38a0b84630deb837f2b7bccf53a62a/test/testpvalink.db#L64-L68

I am unsure about the exact configuration. Specifically, I would like guidance on:

1. Waveform record DB definition – how should the DTYP and INP fields be set to read from the remote PV?

For input type records "INP".  You will also want the "CP" or "CPP" modifier to process on subscription update.

1. Specifying the server IP and port in the INP field.

The PV name lookup process is configured the same as for any PVA client.  eg. using the $EPICS_PVA_ADDR_LIST

1. Specific DBD files and libraries that need to be included to achieve this goal.

pvxsIoc.dbd

1. 
   
2. Any pitfalls, such as array size (NELM) matching or data type requirements.

As usual, NELM (capacity) needs to be large enough.

For example, would a record like this work?

=================================================

record(waveform, "LOCAL:WF") {

    field(DTYP, "pvaClientWaveform")

    field(INP, "PVA:REMOTE:ARRAY:PV@10.200.34.12:5075")

    field(SCAN, "1 second")

    field(NELM, "4096")

}

Something like:

record(aai, "testToFromString:str2") {
    field(FTVL, "DOUBLE")
    field(NELM, "4096")
    field(INP , {pva:{pv:"PVA:REMOTE:ARRAY:PV", "proc":"CPP"}})
}

===============================================

I would greatly appreciate any example .db record, IOC DBD configuration, or startup instructions for properly using a remote PV with waveform records via PVA.

My base EPICS version is : epics-base-R7.0.9-328

Thanks

Varuna Meddage