Power-Aware Synchronization of a Software Defined Clock.

In a distributed system, a common time reference allows each component to associate the same timestamp to events that occur simultaneously. It is a design option with benefits and drawbacks since it simplifies and makes more efficient a number of functions, but requires additional resources and control to keep component clocks synchronized. In this paper, we quantify how much power is spent to implement such a function, which helps to solve the dilemma in a system of low-power sensors. To find widely applicable results, the formal model used in our investigation is agnostic of the communication pattern that components use to synchronize their clocks, and focuses on the scheduling of clock synchronization operations needed to correct clock drift. This model helps us to discover that the dynamic calibration of clock drift significantly reduces power consumption. We derive an optimal algorithm to keep a software defined clock (SDCk) synchronized with the reference, and we find that its effectiveness is strongly influenced by hardware clock quality. To demonstrate the soundness of formal statements, we introduce a proof of concept. For its implementation, we privilege low-cost components and standard protocols, and we use it to find that the power needed to keep a clock within 200 ms from UTC (Universal Time Coordinate) as on the order of 10(-5) W. The prototype is fully documented and reproducible.