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4.2 Interface software

The designation "interface software" is used here for the logical connection between the Microsoft Flight Simulator and the flight simulator cockpit. Basically there are 2 groups of interfacing software:

1. Interfacing software that directly controls cockpit elements. The most obvious example is the software that comes with ready made cockpit parts like a joystick or the pedals. But there are also interface boards that are recognized as an a standard device (e.g. the 32 digital input controller (SIMKITS) is recognized under Windows as a standard Game Controller without any additional driver software).
2. Interfacing software that communicates Microsoft Flight Simulator data to a controller. It is the task of the controller (a separate device) to drive the various cockpit devices. The controller contains the actual programming logic for this (as described in section 5). Thus the interfacing software focuses only on the communication of Microsoft Flight Simulator data to an other computing device and vice versa.

Note that not all interfacing has to be done by means of software as described above. The input for Microsoft Flight Simulator that can be done by means of a keyboard, can also be done by means of keyboard emulation (discussed in section 5).

The table below gives an overview of the approaches that can be followed to interface the Microsoft Flight Simulator from a software technology point of view. A number of suppliers of interface devices (discussed in section 5) offer easy to use software to control their interface boards and prevent that a cockpit builder has to write his own interfacing software.

4.2.1 The Dowson route: FSUIPC

If there would be a Nobel Price for Flight Simulation, one of the holders would be Peter Dowson for his very fundamental and significant contribution to interfacing with the Microsoft Flight Simulator and opening up the market for serious add-on development. Until the introduction of FSX he offered the only serious programming interface for the Microsoft Flight Simulator, facilitating a large add-on community including cockpit builders. His interfacing software FSUIPC (Peter Dowson) is a module that has to be included with the Microsoft Flight Simulator and facilitates the exchange of data with the Microsoft Flight Simulator for programs written by third parties. Based on FSUIPC utilities, programs and gauges interfacing with the Microsoft Flight Simulator are developed by Dowson and many others. Some of this software supports flight simulator cockpit development and will be addressed in other parts of this text. In this section we will focus on the use of the FSUIPC module for interfacing purposes, but it should be said that FSUIPC contains a substantial set of additional features.

The FSUIPC module comes with a SDK that allows developers to interact with this module. It is possible to address FSUIPC from within a self developed module to be included with the Microsoft Flight Simulator, but it is also possible to address FSUIPC from within a separate program. This software can be more or less written in the programming language of your choice. Included are instructions for C/C++, Delphi, Visual Basic, ASM and Borland C++. The actual interfacing by this program is made very simple and limited to 5 instructions as shown in the table below.

Included in the documentation is a long list of offsets (30+ pages) which provides access to almost all relevant variables within Microsoft Flight Simulator. Example:

For running applications using FSUIPC on a separate PC in a network (IPX/SPX or TCP/IP) WideFS (Peter Dowson) was developed. WideFS comes with 2 programs: WideServer and WideClient. The concept of WideFS is that the Microsoft Flight Simulator runs on the server machine also containing WideServer. The program WideClient, together with the utility program runs on an other machine in the network (for programs that place their windows within the Microsoft Flight Simulator window the windows are placed in the WideClient window). In principle one should not notice any effect on frame rates at all. Each server can serve many clients, but each client only talks to one server. WideFS can be used by any utility that uses FSUIPC, it requires the setup of a network, but does not require any programming activities.

For users of the Microsoft Flight Simulator add-on Level-D 767 there is specific software called FSCONV by Nico Kaan that provides new FSUIPC offsets for the Level-D add-on by bridging FSUIPC and the Level-D SDK.

4.2.2 The Microsoft route: SimConnect

In order for third party software to access data and events internal to Flight Simulator X SimConnect is developed. This has been a very significant step in making the Microsoft Flight Simulator a truly open platform. Add-on components for FSX can be written in C, C++, or if the managed API calls are being used, any Microsoft .NET language such as C#.net or VB.net. Typically the components will perform one or more of the following:

• Add the processing for a new complex gauge, or other instrument, to Flight Simulator.
• Replace Flight Simulator processing of one or more events with new logic.
• Record or monitor a flight.
• Extend the mission system of Flight Simulator.
• Create and set the flight plans for AI (non-user) aircraft.
• Set different weather systems.
• Enable hardware to work with Flight Simulator.
• Control an additional camera that the user can optionally select to view.

SimConnect is based on a client-server architecture and sees the Flight Simulator as a server. The data, events, and system calls available via the SimConnect interface support the vast majority of data and events that exist inside FSX.

SimConnect uses asynchronous communication because it is more safe for use in multi-processor or multi threaded applications, it uses processing cycles more efficiently and provides greater server application stability. A publish/subscribe method is used where the client will request a data packet or send an event, and the server will process that request at a time commensurate with the priority level of the request. The process is, however, considered asynchronous since it is never handed over to the client application.

The recommended method of writing an add-on is to build it out-of-process, as an application (an .exe file) rather than in-process, as a library (a .dll file). This is because out-of-process applications provide more stability, if they crash they will typically will not crash FSX, and are easier to build, test and debug. Out-of-process also supports managed code, and therefore applications can be written in .NET languages. The .EXE can be executed (with the same code) on both the same PC as Flight Simulator X or on a different PC using a TCP/IP connection. The TCP/IP communication is handled completely by SimConnect.

The SimConnect SDK including detailed documentation and example code is included with the deluxe edition of FSX. Examples of other sources of information regarding the use of SimConnect are: FSdeveloper, In the pipe and AVSIM SimConnect forum.

When you need to write your own software to interface with FSX then SimConnect is the preferred route to go. It is supported by Microsoft and in the coming period you will see an increase in publications and example source files spread over internet.