Automated Code Generation for DES Controllers Modeled as Finite State Machines

Abstract

Finite State Machines ($\textrm{FSMs}$) are the foundation to design Discrete Event Systems ($\textrm{DESs}$). A $\textrm{FSM}$ that designs a $\textrm{DES}$ model can be further processed using Supervisory Control Theory ($\textrm{SCT}$) to synthesize correct-by-construction software. When applied to industrial-scale $\textrm{DESs}$, $\textrm{FSMs}$ face limitations in the design, synthesis, and implementation steps. Supremica is a straightforward tool that facilitates design and synthesis but does not reach the implementation phase. This requires additional tools to convert $\textrm{FSM}$ models into code. This paper presents the tool DEScMaker, which receives as input an $\textrm{FSM}$ model outputting from Supremica and converts it into implementable C code. Our approach complements Supremica with code generation and allows taking advantage of its intuitive interface, useful simulator, and safe algorithms while automating a task that, in practice, consists of complex manual programming. An example illustrates the tool and quantifies its advantages.

This research was supported by the Brazilian National Council of Scientific and Technological Development (CNPq), under grant number 309946/2020-4, by CAPES (Coordination for the Improvement of Higher Level or Education Personnel), Brazil, financial code 001, FINEP (Funding Authority for Studies and Projects), Brazil, Araucária Foundation, Brazil, and IFC (Catarinense Federal Institute).

Appendices

Appendix 1 Directory Tree of Generated Code

Figure 9 shows the representation of the directory and file structure generated by DEScMaker.

Fig. 9.

Directory tree of generated code.

In this case, the input file has only one supervisor, named “sup”, which results in the files “sup.c” and “sup.h” under “src/supervisors/”. If the file has two or more supervisors, as in the modular approach, all code files and headers are placed in the folder “supervisors”.

Appendix 2 Code Generation Example

Consider the $\textrm{FSM}$ in Fig. 10, corresponding to a supervisor with four states, seven transitions, and three different events. The Supremica file with this automaton was submitted to the DEScMaker, which created the code structure and saved it in “src/supervisors/sup.c”.

Fig. 10.

Simple example of $\textrm{FSM}$ for code generation.

Variables of type Alphabet are declared to create the list of events observed by the supervisor. This creates a variable with reserved memory space for an Alphabet structure, but its fields have no values assigned yet. Next, the alphabet variables are initialized and linked. This creates a list where it is possible to navigate from the first to the last event in the alphabet. In this example, the last element of the ‘sup_e3_evt2’ variable is NULL because there are no more elements in the list. This pattern also repeats when creating the other lists. The listing 1.1 shows the code for declaring, initializing, and linking the alphabet.

Then the variables of type State, for representing the $\textrm{FSM}$ states, are declared as in Listing 1.2.

Once the alphabet and states are defined, the transition lists can be created and linked. Listing 1.3 exemplifies the transitions of the states q0 and q1.

The states are initialized in Listing 1.4, now filled with all the necessary information, especially the pointer to the corresponding list of transitions.

Finally, Listing 1.5 shows the structure of the supervisor, which will compose the list of supervisors (in the file “src/supervisors/supervisor_list.c”) used by the event handler to query the event status and perform transitions. The variable of type ’Supervisor’ is declared and initialized with pointers to the initial state, the current state, the last state (NULL because it has not yet been executed), the first item in the event list, and the supervisor’s name.