Tiny devices have become ubiquitous in people's daily lives. Their applications dictate tight energy budgets, but also require reasonable performance to meet user expectations. To this end, the hardware of tiny devices has been highly optimized, making further optimizations difficult. In this work, we identify a missed opportunity: the bitwidth selection of program variables. Today's compilers directly translate the bitwidth specified in the source code to the binary. However, we observe that most variables do not utilize the full bitwidth specified in the source code for the majority of execution. To leverage this opportunity, we propose BitSpec : a system that performs fine-grained speculation on the bitwidth of program variables. BitSpec is implemented as a compiler-architecture co-design, where the compiler transparently reduces the bitwidth of program variables to their expected needs and the hardware monitors speculative variables, reporting misspeculation to the software, which re-executes at the original bitwidth, ensuring correctness. BitSpec reduces energy consumption by 9.9% on average, up to 28.2% .

This work presents a distributed implementation for processing Maximizing Range Sum (MaxRS) query in Wireless Sensor Networks (WSN). MaxRS query is useful in many spatially-distributed event monitoring and target tracking applications. Given the location and current readings of the nodes, and a rectangle R, MaxRS finds a location of R that maximizes the sum of the readings of all the nodes covered by R. Our system performs MaxRS query in a user-specified time-interval γ and using the result obtained, attempts to maintain a certain degree of energy conservation in the WSN, based on a user-defined threshold δ. Since centralized processing of the raw readings and subsequently determining the MaxRS may incur significant communication overheads, we developed a distributed algorithm to compute MaxRS. We implemented our system in a heterogeneous WSN consisting of TelosB and SunSPOT motes, and illustrate the end-user tools: GUI for specifying required parameters, and real-time visualization of MaxRS solutions and estimated network energy consumption.