Reducing register and phase requirements for synchronous circuits derived using software pipelining techniques

A method based on a modulo scheduling algorithm for software pipelining has been recently proposed to optimize clocked circuits. The resulting circuits are multi-phase clocked circuits, where all clocks have the same period. To preserve the functionality of the original circuit, registers must be placed after minimizing the clock period. The placement of these registers is derived from an arbitrary schedule determined during a clock period minimization step. A good schedule may allow one to decrease the number of registers and the number of phases needed in the final circuit. Decreasing the number of registers contributes to minimizing the area occupied by the circuit and reduces its power consumption; while decreasing the number of phases reduces the complexity of the clock generation and distribution task. In this paper, we propose polynomial-time-solvable methods to choose a good schedule once the clock period is minimized. The methods have been tested on a subject of the ISCAS89 benchmarks. Experimental results show that the number of registers which must be inserted in the final circuit, and the number of phases, have been significantly decreased compared to the case where an arbitrary schedule is chosen.