Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Mon, 18 Oct 2010 15:26:41 -0500

Hi Franck,

On Monday 18 October 2010 07:56:03 Di Maio Franck wrote:
>
> A typical ITER use case:
>
> "Do A at time T",
> - T: a setting controllable by PV(s),
> - A: an action implemented by a record triggered by an event occurring at
> time T.
>
> We are implementing this use case with a module that receives time over
> PTP, so the time shall be expressed with nano-second resolution.
>
> So we need:
> - one unsigned int32 for seconds
> - one (unsigned or not) int32 for fraction of second expressed as
> nano-seconds. Same as time-stamp (TS), right?

True, the same as the epics time-stamp, but that is unfortunately not a 
primitive data type so you can't transfer them around as a simple CA value.

> Maybe 2 longout but I am not sure if UINT32 is OK with longout.
> In addition, we'll have "pulse time", with a specific time origin, so maybe
> also sub or calc records to convert between relative and absolute time.
>
> We'll appreciate advices on the records to be used... Good or bad
> ideas/experiences welcome.

You could use an aSub record type and handle the time-stamp as an array of 2 
DBF_LONG values, that array being a type which both CA and DB links can handle 
properly.  You then write aSub subroutines that process the timestamps as 
needed.

If you're going to need to do a lot of work with time-stamp values you might 
want to consider creating a special-purpose record type that has input and 
output links that transfer those kinds of arrays and that does the relative 
<=> absolute time conversion, or that just calculates the sum and difference 
of two such time-stamp arrays.  A new record type probably doesn't offer 
anything that you can't already do with an aSub record, but it should save a 
few steps configuring all the relevant input and output fields to 2-element 
LONG arrays.

You can stop a record's TIME field from being overwritten by setting its TSE 
field to -2, which would allow aSub code to copy a time-stamp into the TIME 
field.  You can also point the TSEL link of one record to the TIME field of 
another record to make the first record inherit time-stamp values from the 
second.

HTH,

- Andrew
-- 
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scrutinize it closely, and unless the evidence is overwhelming, he will
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System