Experimental Physics and
Industrial Control System

"Kasemir, Kay" <[email protected]> · Mon, 2 Apr 2018 18:21:04 +0000

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