Real-Time Data Connectivity

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# 5. Real-Time Data Connectivity

Many embedded systems and control systems generate a great deal of data, both in real-time and for archival purposes. This data reflects both the current state of the system and the past history of the system. This data is often needed for optimization, analysis, fault diagnosis, graphical display and operator interaction. The tools typically required for data analysis are largely available in the MS-Windows environment, but often the real-time data is generated from a QNX control system. In this case, the connection between QNX and MS-Windows must be a live data connection, rather than a file system or view connection. The data source (a QNX control system), will typically be able to emit messages using the native QNX (FLEET) protocol. Similarly, the data receiver, an MS-Windows application, is able to receive messages using native MS-Windows protocol (DDE). A system designer will generally have no control over the MS-Windows application, such as MS-Excel, Wonderware's InTouch, or other tools from third-party vendors. The design decision to use an MS-Windows program is often made for historical reasons or as a result of a strict feature comparison with available QNX tools. The designer may also have only limited control over the QNX control application, or may not want to incur the performance and reliability penalty associated with a NetDDE implementation in QNX. Unlike the low-level inter-process communication scenario, there is less possibility of having the sender and receiver agree on a communication protocol. Each process must communicate using native IPC.

In this scenario, the Cascade Connect tool from Cogent Real-Time Systems, Inc. provides a real-time data connection that allows any MS-Windows program to exchange real-time data with QNX applications. Cascade Connect comes in two parts: Cascade Connect for the MS-Windows computer, and the Connect Server for the QNX computer. Cascade Connect communicates with the MS-Windows application using DDE, and the Connect Server uses the QNX FLEET protocol to interact with the QNX program. Cascade Connect and the Connect Server communicate with each other over a network using TCP/IP. This facility provides high-speed real-time data connectivity, but does not provide file system or peripheral sharing, and it relies on TCP/IP being installed on both the QNX and MS-Windows computers.

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