converting java method to vhdl

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Using FSM and Datapath will not create a Sudoku game. You need to use NIOS and QSYS. I think you are basically trying to convert your code into optimised hardware version, where you implement the computations only. Which can be done easily using state machines without a datapath.

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What are you on about?

This can be done without NIOS or QSYS with a pure hareware implementation. In this case you would need a FSM and some form of data path.