Re: Long String support in phoebus

["Nonn, Patrick via Tech-talk" <tech-talk at aps.anl.gov>]

Hi everyone,

I would like to clarify, that you have to address the VAL field of a PV specifically and add a $ to that. "caput -S <pv_name>$" will not work. (Because caput addresses <pv_name>$.VAL, that way.) The same is true for CSS, incl. phoebus. I'm mentioning that, because I actually found some old tech-talk entry before I started this thread, where it was also mentioned that you have to add a $ to the pv name, which did not work for that reason.

Let me summarize, what to do, if your lso/lsi won't hold more than 40 characters:

- check the field SIZV, it defaults to 41 (=40 characters)
- check the environment variables EPICS_CA_MAX_ARRAY_BYTES and EPICS_CA_AUTO_ARRAY_BYTES
  For more information, check: https://epics.anl.gov/base/R3-16/1-docs/RELEASE_NOTES.html
- for caput/caget: make sure you use the -S option
- for caput/caget and CSS: Address the pv as <pv_name>.VAL$
- for CSS, incl. Phoebus: check the "max_array_bytes"-setting
- for CSS Phoebus: make sure to set the format property to "String"

Have I forgotten something?

Best Regards,
Patrick

----- Original Message -----
From: "Mark Rivers" <rivers at cars.uchicago.edu>
To: "Patrick Nonn" <patrick.nonn at desy.de>
Cc: "tech-talk" <tech-talk at aps.anl.gov>
Sent: Friday, 10 July, 2020 15:34:24
Subject: Re: Long String support in phoebus

Hi Patrick,


I just tested the waveform and lso records for long string behavior, and the result surprised me.


I loaded this database which has an lso and waveform record each capable of holding 2048 characters.


###################
record(lso, "test_lso") {
  field(SIZV, "2048")
}

record(waveform, "test_wf") {
  field(FTVL, "CHAR")
  field(NELM, "2048")
}
###################

This is a caput of 60 characters to the waveform record using the -S flag.  It works fine.

corvette:~>caput -S test_wf 01234567890234567890123456789012345678901234567890123456789
Old : test_wf
New : test_wf 01234567890234567890123456789012345678901234567890123456789

This is a caput of 60 characters to the lso record with no flags to caput.  Note that it only wrote 40 characters.

corvette:~>caput test_lso 01234567890234567890123456789012345678901234567890123456789
Old : test_lso
New : test_lso                       012345678902345678901234567890123456789

This is a caput of 60 characters to the lso record with the -S flag to caput.  It generates an error.

corvette:~>caput -S test_lso 01234567890234567890123456789012345678901234567890123456789
Old : test_lso
Error from put operation: Invalid element count requested

This is a caput of 60 characters to the lso record .VAL$ field with the -S flag to caput.  It works.

corvette:~>caput -S test_lso.VAL$ 01234567890234567890123456789012345678901234567890123456789
Old : test_lso.VAL$
New : test_lso.VAL$ 01234567890234567890123456789012345678901234567890123456789

This result surprised me.  I thought an lso record and a waveform record would work the same way.  But in order to write to an lso record which has SIZV > 41 you must use the .VAL$ syntax.

cainfo shows that the reason is that an lso record native data type is DBF_STRING while the waveform record is DBF_CHAR.

corvette:~>cainfo test_wf
test_wf
    State:            connected
    Host:             164.54.160.82:40035
    Access:           read, write
    Native data type: DBF_CHAR
    Request type:     DBR_CHAR
    Element count:    2048
corvette:~>cainfo test_lso
test_lso
    State:            connected
    Host:             164.54.160.82:40035
    Access:           read, write
    Native data type: DBF_STRING
    Request type:     DBR_STRING
    Element count:    1


It would probably be good to mention that the .VAL$ syntax is required in the lso record documentation here:
https://epics.anl.gov/base/R7-0/4-docs/lsoRecord.html

Mark












________________________________
From: Nonn, Patrick <patrick.nonn at desy.de>
Sent: Friday, July 10, 2020 7:08 AM
To: Mark Rivers
Cc: tech-talk
Subject: Re: Long String support in phoebus

Using caput does the same, using caput -S fails with "Error from put operation: Invalid element count requested".

----- Original Message -----
From: "Mark Rivers" <rivers at cars.uchicago.edu>
To: "Patrick Nonn" <patrick.nonn at desy.de>
Cc: "tech-talk" <tech-talk at aps.anl.gov>
Sent: Friday, 10 July, 2020 14:05:41
Subject: Re: Long String support in phoebus

What happens if you use caput?


________________________________
From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Nonn, Patrick via Tech-talk <tech-talk at aps.anl.gov>
Sent: Friday, July 10, 2020 6:57 AM
To: tech-talk
Subject: Long String support in phoebus

Hi everyone,

I try to write an lso record with a text entry widget. The string is cut at 40 characters. Is there something to be taken into account, apart from:

preference "org.phoebus.pv.ca/max_array_bytes" set to a high enough number
field SIZV set to a high enough number

Greetings
Patrick