Re: subArray behavior reading just 1 element

[Lucas Russo via Tech-talk <tech-talk at aps.anl.gov>]

Hi Andrew,

Trying to do what you suggested:

test.db:

record(waveform, "wave") {
    field(INP, "[1, 2, 3, 4, 5]")
    field(NELM, "5")
    field(FTVL, "DOUBLE")
    field(PINI, "YES")
    field(FLNK, "subarr")
}

record(subArray, "subarr") {
    field(INP, "wave")
    field(INDX, "1")
    field(MALM, "5")
    field(NELM, "1")
    field(FTVL, "DOUBLE")
}

lerwys@lerwysPC:~$ softIoc -d test.db
Starting iocInit
############################################################################
## EPICS R7.0.5.1-DEV
## Rev. 2021-08-22T23:01-0300
############################################################################
iocRun: All initialization complete
epics>

lerwys@lerwysPC:~$ caget wave

wave 5 1 2 3 4 5
lerwys@lerwysPC:~$ caget subarr
subarr 5 2 0 0 0 0

subarr always returns an array of 5 elements, but I was trying to achieve a subArray of only 1 element. Something like:

lerwys@lerwysPC:~$ caget subarr
subarr                         2

Is that possible?

Thanks again!

Lucas

On Wed, Sep 1, 2021 at 5:15 PM Johnson, Andrew N. <anj at anl.gov> wrote:

Hi Lucas,

Please read the “Array Parameters” section of the Record Reference page for the subArray record. Jueri is correct if you need to be able to access any element of the original waveform; if you only need one of the first 10 elements say, you can set MALM to 10.

- Andrew

On Sep 1, 2021, at 2:57 PM, Lucas Russo via Tech-talk <tech-talk at aps.anl.gov> wrote:

Hi Jueri,

Sure. But then caget returns a waveform of MALM elements instead of just 1 element. I wanted to have a subarray of 1 element. Is that possible? Or does it even make sense to do with subarray?

Thanks,

Lucas

On Wed, Sep 1, 2021, 16:53 Tagger, Jueri <jtagger at bnl.gov> wrote:

Your MALM of subarray must be equal to NELM of waveform

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> On Behalf Of Lucas Russo via Tech-talk
Sent: Wednesday, September 1, 2021 3:43 PM
To: EPICS Tech Talk <tech-talk at aps.anl.gov>
Subject: subArray behavior reading just 1 element

 

Hello everyone,

 

I have a quick question,

 

I was trying to get subArray to read the second (or any other than the first) element from a waveform record, like this:

 

cat << EOF > test.db
record(waveform, "wave") {
    field(INP, "[1, 2, 3, 4, 5]")
    field(NELM, "5")
    field(FTVL, "DOUBLE")
    field(PINI, "YES")
    field(FLNK, "subarr")
}

record(subArray, "subarr") {
    field(INP, "wave")
    field(INDX, "1")
    field(MALM, "1")

    field(NELM, "1")
    field(FTVL, "DOUBLE")
}
EOF

 

softIoc -d test.db

 

But it doesn't work as subarr INDX >= MALM (https://github.com/epics-base/epics-base/blob/R7.0.4/modules/database/src/std/rec/subArrayRecord.c#L308), and it always return the first element of the waveform. Is that the expected behavior? This seems odd to me as INDX refers to an index of the waveform record and MALM refers to the maximum number of elements of the subarray record. But I might be missing something.

 

Using EPICS 7.0.4.1

 

Thanks!

 

Lucas

-- 

Complexity comes for free, simplicity you have to work for.