State retention for power gated design with non-uniform multi-bit retention latches

Retention registers/latches are commonly applied to power-gated circuits for state retention during the sleep mode. Recent studies have shown that applying uniform multi-bit retention registers (MBRRs) can reduce the storage size, and hence save more chip area and leakage power compared with single-bit retention registers. In this paper, a new problem formulation of power-gated circuit optimization with nonuniform MBRRs is studied for achieving even more storage saving and higher storage utilization. An ILP-based approach is proposed to effectively explore different combinations of nonuniform MBRR replacement. Experiment results show that the proposed approach can reduce 36% storage size, compared with the state-of-the-art uniform MBRR replacement, while achieving 100% storage utilization.