Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Mon, 28 Oct 2013 16:22:29 -0500

Hi Brian,

On 10/28/2013 03:56 PM, Vaughn, Brian wrote:

When configuring a Labview EPICS Server I/O Server, one is able to
select from more data types than are available when configuring a
Labview EPICS Server I/O Client. For example, you can create a
network-published shared variable with a data type: array of booleans,
and link it to an EPICS PV, but when trying to create a corresponding PV
in the client, there is no option for the data type: array of booleans.
The same situation exists for unsigned integers, etc.

I don't know anything about the LabView software you're asking about,

but the underlying Channel Access protocol only supports a limited set

of basic data types which probably map directly to the set you're asking

about for your client. The CA set is documented here:

  http://www.aps.anl.gov/epics/base/R3-14/12-docs/CAref.html#Channel

Note that there are no unsigned integer types in that list, nor a

boolean one.

The IOC database software is in a similar position, it supports unsigned

integer types, and has a standard method of converting those into types

for the CA protocol to transport.

A CA client can request the value of any channel or put a value to any

channel using any type it likes, and the server must attempt to convert

the data to/from that type if it can. However that conversion takes

place on the server, and it is usually better for each client to look at

and use the channel's native type for CA requests since that reduces the

load on the (shared) server. I'm guessing that's probably what the Auto

data type does that you also mentioned, but as I said above I don't use

LabView so I'm only speculating there.

HTH,

- Andrew
--
Advertising may be described as the science of arresting the human
intelligence long enough to get money from it. -- Stephen Leacock

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System