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Paper details
Number 4 - December 2020
Volume 30 - 2020
Improving characteristics of LUT-based Mealy FSMs
Alexander Barkalov, Larysa Titarenko, Kamil Mielcarek
Abstract
Practically, any digital system includes sequential blocks represented using a model of finite state machine (FSM). It is very
important to improve such FSM characteristics as the number of logic elements used, operating frequency and consumed
energy. The paper proposes a novel technology-dependent design method targeting a decrease in the number of look-up
table (LUT) elements and their levels in logic circuits of FPGA-based Mealy FSMs. It produces FSM circuits having three
levels of logic blocks. Also, it produces circuits with regular systems of interconnections between the levels of logic. The
method is based on dividing the set of internal states into two subsets. Each subset corresponds to a unique part of an
FSM circuit. Only a single LUT is required for implementing each function generated by the first part of the circuit. The
second part is represented by a multi-level circuit. The proposed method belongs to the group of two-fold state assignment
methods. Each internal state is encoded as an element of the set of states and as an element of some of its subsets. A
binary state assignment is used for states corresponding to the first part of the FSM circuit. The one-hot assignment is
used for states corresponding to the second part. An example of FSM synthesis with the proposed method is shown. The
experiments with standard benchmarks are conducted to analyze the efficiency of the proposed method. The results of
experiments show that the proposed approach leads to diminishing the number of LUTs in the circuits of rather complex
Mealy FSMs having more than 15 internal states. The positive property of this method is a reduction in energy consumption
(without any overhead cost) and an increase in operating frequency compared with other investigated methods.
Keywords
FPGA, LUT, Mealy FSM, structural decomposition, two-fold state assignment, energy consumption