Hardware Description of Event-driven Systems by Translation of UML Statecharts to VHDL

We present a complete implementation prototype of the classic Fly-n-Shoot game on an FPGA. This is a famous game that has been described in the past using UML statecharts as an event-driven embedded system. Because it has a rather complex functionality, attempting to describe it using a hardware description language (HDL), such as VHDL or Verilog, with the goal of deploying on a real FPGA becomes challenging. As such, brute-force attempts to write HDL descriptions are prone to errors and subject to long design times. Hence, in this paper, we describe a practical approach for translating UML statecharts used to specify event-driven embedded systems into VHDL code written using the popular two-process coding style. This approach consists of a set of mapping rules from statecharts concepts into VHDL constructs. The efficacy and correct by design characteristics of the presented approach are due to the use of two-process VHDL coding to describe the hierarchical finite state machine (FSM) corresponding to the UML statecharts. This gives the designer better control over the current and next state signals of the FSMs, it is more modular or object oriented, and makes development and debugging much easier. We apply the proposed approach to implement a prototype of the classic Fly-n-Shoot game. The implementation is verified successfully on real hardware, the DE1-SoC FPGA development board, that uses a Cyclone IV FPGA chip.