Off-chip buses account for a significant portion of the total system power consumed in embedded systems. Bus encoding schemes have been proposed to minimize power dissipation, but none has been demonstrated to be optimal with respect to any measure. In this paper, we give the first provably optimal and explicit (polynomial-time constructible) families of memoryless codes for minimizing bit transitions in off-chip buses. Our results imply that having access to a clock does not make a memoryless encoding scheme that minimizes bit transitions more powerful.

This paper contains a tutorial on bus-encoding techniques that target low power dissipation. Three general classes of codes, i.e., algebraic, permutation-based, and probability-based, are reviewed. A new mathematical framework for unifying the power-aware algebraic coding techniques based on the notion of leader sets is also presented.

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