Experimental Physics and
Industrial Control System

"Hammonds, John" <[email protected]> · Mon, 20 Oct 1997 16:03:50 -0500

I am looking at using EPICS for a data acquisition system for an array
of detectors.  We are thinking of using subArray records to hold the
data but need some flexibility that does not seem to be worked in.  

First of all we will routinely rebin the array from one run to the next
so that it would be nice to resize the array on the fly.
We often combine data on the fly to conserve memory.  Again, we change
how this is done on the fly.

To get around the resizing problem I was thinking about defining one
large subArray record that would predefine the entire data space for the
crate.  I would then use a subArray record that points into the larger
dataspace to allow access data for each detector.  For now I can limit
myself to the 16KB limit for CA transfers within this limit.  This also
allows data to be binned together on the fly since two of the smaller
subArrays can point to the same space.  

One problem that I have with this is that the smaller subarrays seem to
copy the data from the larger subArray to the smaller one.  This seems
to be a waste of both time (for copy) and memory for this purpose.  What
I was thinking of doing was making the BPTR of the smaller array point
directly to the BPTR of the larger array (+the INDX offset).

Has anyone done this or does anyone see a problem/improvement with this
approach?

------------------------------------------------------------------------
----
John P. Hammonds
Intense Pulsed Neutron Source
Argonne National Laboratory
(630)252-5317

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System