Using tcp/ip as an I/O interface
StateWORKS RTDB is a tcp/ip server. All attributes of each object in RTDB can be accessed by tcp/ip clients. A client connects to the RTDB server using two sockets: Request and Event. The Request (R) socket is used for queueing of object attributes. The Event (E) socket delivers object attributes that are registered as “advise” in RTDB.
The primary goal of the server/client model of the RTDB has been communication with a User Interface. When the tcp/ip communication began to be used for input/output purposes we could extend the StateWORKS server/client model very easily by completing attributes of corresponding object by a concept of RawData. The completion of Raw data are required for objects: DI, DO, NI, NO, the objects CMD, XDA, PAR and DAT possessing per se the raw data values.
We have add another technical note to our web site describing the tcp/ip communication in RTDB. You may download the note http://www.stateworks.com/active/download/TN24-Using-tcpip-as-io.pdf to study the details.
As the i/o interface requires a very high reliability the implementation of tcpip used for an io interface is a true challenge. Our solution with Request and Events channels fulfills the i/o requirements. That goal has been achieved by careful design taking into account several possible distortion of the tcpip link.
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