Re: Dynamically changing HIHI PV field

[Andrew Johnson via Tech-talk <tech-talk at aps.anl.gov>]

    Hi Marco,

On 4/12/22 8:39 AM, Marco A. Barra Montevechi Filho via Tech-talk wrote:

I have an equipment which has the HIGH field configurable in the hardware. We already have a PV that reads it, but it is currently an entire PV, and not a field of another existing PV.

Im trying to get that PV result and put it in the HIGH field of another PV. Something like:

record(ai, "MY:PV") {

  field(HIHI, 10)

  field(HIGH, "ANOTHER:PV:HIGH:LIMIT PP")

  field(LOW, -1)

  field(LOLO, -5)

  field(HHSV, MAJOR)

  field(HSV, MINOR)

  field(LSV, MINOR)

  field(LLSV, MAJOR)

}

but each try of mine gets either syntax error or 'Can't set "MY:PV.HIGH" to "ANOTHER:PV:HIGH:LIMIT"'. Am i doing something wrong? Is this approach even possible?

    To explain the "why" behind Torsten's answer, you can look up the
    data type of the ai record's HIGH field on it's Record
      Reference page:

Field	Summary	Type	DCT	Default	Read	Write	CA PP
HIHI	Hihi Alarm Limit	DOUBLE	Yes		Yes	Yes	Yes
HIGH	High Alarm Limit	DOUBLE	Yes		Yes	Yes	Yes
LOW	Low Alarm Limit	DOUBLE	Yes		Yes	Yes	Yes
LOLO	Lolo Alarm Limit	DOUBLE	Yes		Yes	Yes	Yes

    The type given there is DOUBLE, so you can only set the field to a
    value which is a double-precision floating point number — that's why
    you were getting those errors, it can't accept a PV name. If you
    want the high alarm limit of your ai record to be updated whenever
    the value reported from the hardware changes you have to arrange for
    some other record to copy the new value there. Torsten's ao record
    demonstrates one way to do this (there are others which might be
    appropriate in different circumstances):

record(ao, "$(PREFIX)$(MOTOR_NAME)-CfgVELO-RB_")

{

    field(PREC, "$(PREC)")

    field(DOL,  "$(PREFIX)$(MOTOR_NAME)-CfgVELO-RB CP")

    field(OUT,  "$(PREFIX)$(MOTOR_NAME).VELO")

    field(OMSL, "closed_loop")

}

    The DOL and OUT fields of the ao
      record type are both links; DOL is an INLINK (input link), so
    it fetches a value from the record named in the field, and OUT is an
    OUTLINK (output link), so it writes a value to the named record. The
    CP flag at the end of the input link tells the record to monitor
    that PV using Channel Access, and to cause the ao record to be
    processed whenever the value changes thus sending the new value to
    the other record. Using CP on an input link is normally better than
    making the record process at some periodic rate because it will
    process immediately, but only when it actually needs to.
    
    - Andrew
-- 
Complexity is free, it's Simplicity that takes work.