Re: Waveform to single ai (again)

[Érico Nogueira Rolim via Tech-talk <tech-talk at aps.anl.gov>]

On 29/04/2025 09:17, Dr. Simon Friederich wrote:

Dear Erico,

Thank you very much for the reply and the explanation concerning the MALM field.

I am no programming expert: Does it matter (concerning server/network resources?), if I create 128 more or less empty arrays? Or is NELM the important field that I can set to 1?

Concerning network resources, 128 empty arrays won't be an issue, most of the time even CA will only transmit the valid array elements. They will take up more RAM in your server, though, because the underlying array can have up to MALM elements, even if you're only taking NELM of them (shouldn't be an issue, I think, unless it's an embedded application with very limited resources).

That said, my concern about array PVs instead of scalar ones was that it makes interaction with clients more complicated. When using pyepics, the values are returned as a single element array, so you always need to unpack that, and the Archiver Appliance will archive it as an array, so the basic automatic visualization of archived data might not work out of the box.

Best regards
Simon

Am 28.04.2025 um 17:59 schrieb Érico Nogueira Rolim:

Hi Simon!

I'm responding inline.

On 28/04/2025 11:54, Dr. Simon Friederich via Tech-talk wrote:

Dear EPICS-Community,

I have a 128 channel power supply for magnets.
Every 10 seconds a waveform record reads the measured voltages and
currents for all channels (transmitted as one string from the device):
Pattern send by device = U0, I0, U1, I1, U2, I2,..., U127, I127

    record(waveform, "$(WEDLKI)imem_get")
    {
      field(DESC, "Read current of all channels 0-127")
      field(DTYP, "stream")
      field(INP,  "@wedlkiste.proto getmemarea $(PORT)")
      field(SCAN, "10 second")
      field(NELM, "256")
      field(FTVL, "DOUBLE")
      field(PREC, "7")
    }


Now I want to put/assign these values to single ai-records for the
different magnets, i.e. in my substition file I have the channel
number as macro (+Prefix,+Subprefix,etc.):
channel = $(CH) = 0, 1, 2, ..., 127

I now need to extract
    Index_voltage = 2*$(CH)
    Index_current = 2*$(CH) + 1


I am aware of array filters, e.g. $(WEDLKI)imem_get.VAL[INDEX], which
would fit my needs, but I don't know how to calculate the INDEX for this.

    record (ai, "$(P)$(R)i_get_ai")
    {
        field(DESC, "Extr curr for each channel")
        field(INP,  "$(WEDLKI)imem_get.[$(2*CH+1)] CP")  #
unfortunately that does not work
        field(EGU,  "A")
        field(PREC, "7")
    }

Maybe you could try computing the string using sCalcout? Though I think
the solution with subArray below is better.

I could calculate this by hand and enter the INDEX via Macro, but I'd
like to keep my substition file simple:
file ./db/debug_wedlerchannels.db {
  pattern
  {CH, P, R, INDEX} # not desired to calculate INDEX by hand
  { 0, wed:, c0:, 1}
  { 1, wed:, c1:, 3}
  ...
  { 6, wed:, c6:, 13}
  { 7, wed:, c7:, 15}
  ...
  { 13, wed:, c13:, 27}
  { 14, wed:, c14:, 29}
  ....
}

Do you have a suggestion for me how to solve this?

I've also tried a single element subarray and calculated INDX via a
calc record. But unfortunately the single values do only refer to the
first value (index = 0) and are not updated although I've added the
"CP" flag.

    record(calcout, "$(P)$(R)__calci_INDX")
    {
        field(DESC, "Calcuate the index for the subArray")
        field(INPA, "$(P)$(R)i_get CP")
        field(CALC, "(2*$(CH))+1")
        field(OUT,  "$(P)$(R)i_get.INDX NPP") # works, or at least
caget shows that i_get.INDX is correct
        field(DISP, 1)
    }

    record (subArray, "$(P)$(R)i_get")
    {
        field(DESC, "Extr curr for each channel")
        field(SCAN, "Passive")
        field(INP,  "$(WEDLKI)imem_get CP") # Process linking record
every time the target record processes
        field(FTVL, "DOUBLE")
        field(MALM, "1")
        field(NELM, "1")
        field(EGU,  "A")
        field(PREC, "7")
    }

Using a subArray seems the easiest to scale.

The issue you're having with subArray is that MALM needs to be at least
big enough to fit the input array up to the index you're grabbing. I
faced the same issue with [1], where reading the last 80 elements of a
160 value array required MALM=160.

One thing to note with this is that your PVs will be arrays with a max
count of MALM, so it might be interesting to you to simplify client
interaction by adding an additional ai record reading from i_get. That
would even allow you to use a single subArray with NELM=2, which reads
voltage and current, and your separate ai records read from hardcoded
indexes 0 and 1 using CA filters.

Some background:
The imem_get-PV is on the same IOC. Currently we use  EPICS R7.0.7.

Thank you very much in advance.
Best regards
Simon

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