Experimental Physics and
Industrial Control System

Mark Rivers <[email protected]> · Mon, 2 Apr 2018 19:42:49 +0000

The areaDetector pvAccess viewer

https://github.com/areaDetector/ADViewers/blob/master/ImageJ/EPICS_areaDetector/EPICS_NTNDA_Viewer.java

puts a monitor on the PV structure using the generic "field()" request. It then does introspection to find the fields it is interested in.  It is not completely generic since it is expecting an NTNDArray structure, but you can get idea of how to do the introspection.

Mark

Sent from my iPhone

On Apr 2, 2018, at 1:21 PM, Kasemir, Kay <[email protected]<mailto:[email protected]>> wrote:

Hi:

Steve wrote:
Knowing only the name of the variable, the client can request the structure. For example, using the command-line pvget utility . . .
$ pvget BL6:Det:Metadata
BL6:Det:Metadata
structure
 time_t timeStamp 2018-04-02T13:32:08.794 19815342
 epics:nt/NTScalar:1.0 proton_charge
    double value 0
  epics:nt/NTScalarArray:1.0 time_of_flight
      uint[] value []
  epics:nt/NTScalarArray:1.0 pixel
      uint[] value []
. . . tells me that the variable BL6:Det:Metadata has a structure consisting of a timeStamp, a NTScalar value for proton_charge, and NTScalarArrays for time_of_flight and pixel.

pvget dumps the structure and shows the values.
If the structure contains arrays with many elements, it might be a bit much to dump on the console.

With "pvinfo" you get just the structure layout, sans values:

$ pvinfo  BL6:Det:Metadata
CHANNEL  : BL6:Det:Metadata
STATE    : CONNECTED
ADDRESS  : ...
structure
   time_t timeStamp
       long secondsPastEpoch
       int nanoseconds
       int userTag
   epics:nt/NTScalar:1.0 proton_charge
       double value
   epics:nt/NTScalarArray:1.0 time_of_flight
       uint[] value
   epics:nt/NTScalarArray:1.0 pixel
       uint[] value

So pvinfo would allow you to inspect the structure, and then you use pvget to fetch the pieces of interest.
As Steve mentioned, to make sense  of the structure you might need additional info.
For instance, you see that "pixel" is an array of uint. But what does that mean?

-Kay

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System