Re: Labview EPICS server and client data types.

[Andrew Johnson <anj@aps.anl.gov>]

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
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