Symbolic synthesis of clock-gating logic for power optimization of control-oriented synchronous networks

Abstract

Recent results have shown that clock-gating techniques are effective in reducing the total power consumption of sequential circuits. Unfortunately, such techniques assume the availability of the state transition graph of the target system, and rely on explicit algorithms whose complexity is polynomial in the number of states, that is, exponential in the number of state variables. This assumption poses serious limitations on the size of the circuits for which automatic gated-clock generation is feasible. In this paper we propose fully symbolic algorithms for the automatic extraction and synthesis of the clock-gating circuitry for large control-oriented sequential designs. Our techniques leverage the compact BDD-based representation of Boolean and pseudo-Boolean functions to extend the applicability of gated-clock architectures to designs implemented by synchronous networks. As a result, we can deal with circuits for which the explicit state transition graph is too large to be generated and/or manipulated. Moreover, symbolic manipulation techniques allow accurate probabilistic computations; in particular, they enable the use of non-equiprobable primary input distributions, a key step in the construction of models that match the behavior of real hardware devices with a high degree of fidelity. The results are encouraging, since power savings of up to 36% have been obtained on controllers containing up to 21 registers.