A Rewriting Algorithm to Generate AROM-free Fully Synchronous Circuits

A Field Programmable Gate Array (FPGA) is used to embed a circuit designed by users instantly. FPGAs can be used for implementing hardware algorithms. Most of FPGAs have Configurable Logic Blocks (CLBs) to implement combinational and sequential circuits and block RAMs to implement Random Access Memories (RAMs) and Read Only Memories (ROMs). Circuit design that minimizes the number of clock cycles is easy if we use asynchronous read operations. However, most RAMs and ROMs in modern FPGAs support synchronous read operations, but do not support asynchronous read operations. It is one of the main difficulties for users to implement hardware algorithms using RAMs and ROMs with synchronous read operations. The main contribution of this paper is to provide one of the potent methods to resolve this problem. We assume that a circuit using asynchronous ROMs designed by a user is given. Our goal is to convert this circuit into an equivalent circuit with synchronous ROMs. We first clarify the condition that a given circuit with asynchronous ROMs can be converted into a circuit without asynchronous ROMs. For this purpose, we will show an algorithm that can generate a circuit with synchronous ROMs, whenever the original circuit with asynchronous ROMs satisfies this condition. Using our conversion algorithm, users can assume that FPGAs support asynchronous ROMs when they design their circuits. Finally, we will show that we can generate an almost equivalent circuit with synchronous ROMs by modifying the circuit even if it does not satisfy this condition.