---------------------------------------------- TrueTime 1.5 Example: Task Synchronization using Monitors Directory: $DIR/examples/synch----------------------------------------------1. INTRODUCTIONThis example shows how to use monitors to obtain mutual exclusion inTrueTime. A cascaded controller for a ball-and-beam process (3rd ordersystem) is implemented using separate tasks for the two loops in thecascade. The output from the outer controller is used as input to theinner controller and is communicated using a global variable. Thisvariable is a shared resource, and mutual exclusion is achieved by aTrueTime monitor.2. COMPILING THE SIMULATION FILES2.1 Configuring the TrueTime Environment    Before starting Matlab, you must set the environment variable    TTKERNEL to point to the directory with the TrueTime kernel files:        Unix/Linux: > export TTKERNEL=$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. For    this example only the m-file approach is provided.    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.3. SIMULATIONSOpen the model synch.mdl to run the simulation. - Study the initialization function (synch_init.m). This creates two  tasks for the outer and inner loop, respectively. A global variable,  outerU, is used for task communication. This variable is the output  from the outer controller (thus its name) and is used as reference  for the inner controller. Finally, a TrueTime monitor is created.- Study the code functions for the controller tasks (outercode.m and  innercode.m). To ensure that no further instructions are executed in  the case that ttEnterMonitor fails, this primitive needs to be called  from its own segment (since all code of a TrueTime segment is executed  at once before scheduling decisions are made). The same holds for   ttExitMonitor to make sure that no further code is executed in the  case a context switch will occur when the monitor is released.- Study the monitor schedule of the simulation. This graph displays when   the various tasks have been holding the monitor during the simulation.- Try modifying the periods of the tasks to change the phasing and to see   which loop that is most sensitive to slower sampling.