----------------------------------------------- TrueTime 1.5 Example: Distributed Control System Directory: $DIR/examples/distributed-----------------------------------------------1. INTRODUCTIONThis example simulates distributed control of a DC-servo. The examplecontains four computer nodes, each represented by a TrueTime kernelblock. A time-driven sensor node samples the process periodically andsends the samples over the network to the controller node. The controltask in this node calculates the control signal and sends the resultto the actuator node, where it is subsequently actuated. Thesimulation also involves an interfering node sending disturbingtraffic over the network, and a disturbing high-priority taskexecuting in the controller node.2. COMPILING THE SIMULATION FILES2.1 Configuring the TrueTime Environment    Before starting Matlab, you must set the environment variable    TTKERNEL to point to the directory with the TrueTime kernel files:        Unix/Linux: > export TTKERNEL=$DIR/kernel        Windows:  Control Panel / System / Advanced / Environment Variables    Then add the following lines to your MATLAB startup script. This    will set up all necessary paths to the TrueTime kernel files.        addpath(getenv('TTKERNEL'))        init_truetime;2.2 Compilation    As described in the reference manual it is possible to write a    TrueTime simulation (i.e. the code functions for the tasks and the    initialization commands) either as m-files or as C++ functions.    Both approaches are provided for this example and the compilations    needed for the respective alternatives are described below.    2.2.1 Matlab version           Since the TrueTime archive contains pre-compiled files, no         compilation is required to run TrueTime in the Matlab version.         However, if needed, the files may be re-compiled by issuing          the command make_truetime from the command prompt.    2.2.2 C++ version            Compilation of the init scripts of the four computer blocks is        performed by the m-file make.m. Run this file from the Matlab        command prompt:        >> make            NOTE: If changes are made to the code functions or the        initialization commands, the affected init scripts need to be        re-compiled. Copy and paste from make.m to compile the        relevant files individually.    3. SIMULATIONSOpen the model distributed.mdl to run the simulation.  - Run a first simulation without disturbing traffic and without   interference in the controller node. This is obtained by setting the   variable BWshare in the code function of the interfering node to   zero, and by commenting out the creation of the task 'dummy' in   controller_init. In this case we will get a constant round-trip delay   and satisfactory control performance. Study the network schedule and   the resulting control performance. - Switch on the disturbing node and the interfering task in the   controller node. Set the variable BWshare to the percentage of the   network bandwidth to be used by the disturbing node. Again study the   network schedule and the resulting control performance. Experiment   with different network protocols and different scheduling policies in   the controller node.