SYNTHESIS OF VHDL-MODEL OF A FINITE STATE MACHINE WITH DATAPATH OF TRANSITIONS
Authors: Barkalov A. A. , Titarenko L. A. , Babakov R. M. 
Published: February 2024

Context. The problem of building a program model of a finite state machine with datapath of transitions using VHDL language is considered. The model synthesis process is identified with the synthesis of this type of finite state machine, since the built model can be used both for the analysis of the device’s behavior and for the synthesis of its logic circuit in the FPGA basis. The object of the research is the automated synthesis of the logic circuit of the finite state machine with the datapath of transitions, based on the results of which numerical characteristics of the hardware expenses for the implementation of the state machine circuit can be obtained. This makes it possible to evaluate the effectiveness of using this structure of the finite state machine when implementing a given control algorithm.
Objective. Development and research of a VHDL model of a finite state machine with datapath of transitions for the analysis of the behavior of the state machine and the quantitative assessment of hardware expenses in its logic circuit.
Method. The research is based on the structural diagram of a finite state machine with datapath of transitions. The synthesis of individual blocks of the structure of the state machine is carried out according to a certain procedure by the given graph-scheme of the con-trol algorithm. It is proposed to present the result of the synthesis in the form of a VHDL description based on the fixed values of the states codes of the state machine. The process of synthesizing the datapath of transitions, the block of formation of codes of transitions operations and the block of formation of microoperations is demonstrated. VHDL description of that blocks is carried out in a synthesizable style, which allows synthesis of the logic circuit of the finite state machine based on FPGA with the help of modern CAD and obtaining numerical characteristics of the circuit, in particular, the value of hardware expenses. To analyze the correctness of the synthesized circuit, the process of developing the behavioral component of the VHDL model, the function of which is the generation of input signals of the finite state machine, is considered. The classical combination of the synthesizable and behavioral parts of the model allows presenting the results of the synthesis of a finite state machine with datapath of transitions as a separate project that can be used as a structural component of the designed digital system.
Results. Using the example of an abstract graph-scheme of the control algorithm, a VHDL model of a finite state machine with datapath of transitions was developed. With the help of CAD AMD Vivado, a synthesis of the developed model was carried out and behavioral modeling of the operation of the finite state machine circuit was carried out. The results of the circuit synthesis made it possible to obtain the value of hardware expenses when implementing the circuit in the FPGA basis. According to the results of behavioral modeling, time diagrams were obtained, which testify to the correctness of the implementation of the functions of transitions and outputs of the synthesized state machine.
Conclusions. In traditional VHDL models of finite state machines, the states do not contain specific codes and are identified using literals. This allows CAD to encode states at its own discretion. However, this approach is not suitable for describing a finite state machine with datapath of transitions. The transformation of states codes using a set of arithmetic and logic operations requires the use of fixed values of states codes, which determines the specifics of the VHDL model proposed in this paper. This and similar models can be used, in particular, in the study of the effectiveness of a finite state machine according to the criterion of hardware expenses in the device circuit.