I am currently unaware of any OPC servers/clients running on any platform other than NT, w2k, win98, and winCE. The OPC foundation is currently working on the OPC-XML spec that will <hopefully> allow for platform independent clients in the form of web-browsers. Perhaps the OPC foundation website has details.
I believe WindRiver has an OPC Server on it's RTOS.
http://www.windriver.com/html/vxopc.html#
Best,
B.O. Aug. 24, 2001
--
Robert Old, System Architecture, [email protected]
Siemens Building Technologies, Inc., HVAC Division
1000 Deerfield Pkwy., Buffalo Grove, IL 60089-4513 USA
Phone: +1(847)941-5623, Fax: +1(847)419-2401
There is a lot of interest in moving the OPC model from DCOM to CORBA. Apparently it is not too easy to say anything polite about DCOM in the process control environment.
> Is MsWindow is the only platform which I can develop and run OPC
> servers/clients on? How about Linux?
The OMG has been doing some work on "OPC-Like" interfaces (my term). The work is a joint effort of the manufacturing domain task force and the utility DTF. See the Data Acquisition from Industrial Systems (DAIS) specification at:
http://www.omg.org/homepages/mfg/mfgmesmc.htm#DAISRFP
OPC is quite primitive when it comes to structured data (can't handle it). DAIS overcomes this. The result is a platform independent
interface for which OPC is a subset on the Windows platform.
Ralph Mackiewicz wrote:
> OPC is quite primitive when it comes to structured data (can't handle
> it). DAIS overcomes this. The result is a platform independent
> interface for which OPC is a subset on the Windows platform.
Some comments to avoid wrong interpration of this statement. OPC can handle structured data, i.e. Data Access Server can send it to clients and
vice versa. The problem is about the type information. There is not specifiec way a client can use to query for type information. OPC space
only knows simple types and arrays. The strcut would be exchanged as an array.
DCOM (on which OPC is based) of course can also handle strcuts, this is called user defined type. But special marshalling code is needed. This
would result in problems, since it is difficult to know which strcuts are of interest.
While this is true it is mostly of no value in exchanging structured data unless you happen to know the structure of the data ahead of time. Conveying type information (or the ability to discover the type) with structured data is essential to any practical use of structured data. This is a major (and unneccessary) shortcoming of OPC that is addressed by DAIS.
There are solutions to this and still use OPC but they are outside of OPC. For instance, the OPC servers offered by my company allow the client to group the elements of the structure into an OPC group. OPC treats these as separate data elements but our software treats them as a single data object that has a single access of the entire
structure on the network side.