The emergence of low-power 32-bit Systems-on-Chip (SoCs), which integrate a 32-bit MCU, radio, and flash, presents an opportunity to re-examine design points and trade-offs at all levels of the system architecture of networked sensors. To this end, we develop a post-SoC/32-bit design point called Hamilton, showing that using integrated components enables a ~$7 core and shifts hardware modularity to design time. We study the interaction between hardware and embedded operating systems, identifying that (1) post-SoC motes provide lower idle current (5.9 μA) than traditional 16-bit motes, (2) 32-bit MCUs are a major energy consumer (e.g., tick increases idle current >50 times), comparable to radios, and (3) thread-based concurrency is viable, requiring only 8.3 μs of context switch time. We design a system architecture, based on a tickless multithreading operating system, with cooperative/adaptive clocking, advanced sensor abstraction, and preemptive packet processing. Its efficient MCU control improves concurrency with ~30% less energy consumption. Together, these developments set the system architecture for networked sensors in a new direction.

Although TCP has widespread adoption in the Internet, wireless sensor networks (WSNs) generally use simpler UDP-based protocols. The few existing TCP implementations for sensor network operating systems do not support all of the features of TCP. We present a full-scale TCP implementation for sensor networks, called TCPlp, based on the TCP protocol logic of the FreeBSD Operating System. Our implementation demonstrates that full-scale TCP can run within the resource constraints of a modern WSN platform, and serves as a vehicle to explore the benefits of using a full TCP stack in the WSN setting. We showcase TCPlp via three applications of TCP: (1) reliable data collection in the context of an application, (2) an interactive configuration/debug shell, and (3) a mote-based web server.

Operating systems and applications in the built environment have relied upon central authorization and management mechanisms that restrict their scalability, especially with respect to administrative overhead. We propose a new set of primitives encompassing syndication, security, and service execution that unifies the management of applications and services across the built environment, while enabling participants to individually delegate privilege across multiple administrative domains with no loss of security or manageability. We show how to leverage a decentralized authorization syndication platform to extend the design of building operating systems beyond the single administrative domain of a building. The authorization system leveraged is based on blockchain smart contracts to permit decentralized and democratized delegation of authorization without central trust. Upon this, a publish/subscribe syndication tier and a containerized service execution environment are constructed. Combined, these mechanisms solve problems of delegation, federation, device protection and service execution that arise throughout the built environment. We leverage a high-fidelity city-scale emulation to verify the scalability of the authorization tier, and briefly describe a prototypical democratized operating system for the built environment using this foundation. This is an extension of work presented in Ref. [3].

Modern IoT prototyping platforms fall short in terms of energy efficiency, connectivity and software programming practices. We present the design of a new hardware and software platform that addresses these shortcomings by bringing together Mobile, Wearable, Maker and Wireless Sensor Network technologies to enable rapid prototyping with a high degree of synergy and energy efficiency. This is achieved in part by leveraging the Memory Protection Unit on modern microcontrollers along with a novel syscall interface to provide kernel / user isolation and a clean concurrency model. Such a design allows a wide range of languages to be used for application development without significant adaptation. We demonstrate how careful choice of application language allows the naturally asynchronous nature of embedded programming to be expressed cleanly and powerfully. Finally we evaluate the platform in several integrated use cases, providing examples of the capabilities introduced by Synergy.

Rust, a new systems programming language, provides compile-time memory safety checks to help eliminate runtime bugs that manifest from improper memory management. This feature is advantageous for operating system development, and especially for embedded OS development, where recovery and debugging are particularly challenging. However, embedded platforms are highly event-based, and Rust's memory safety mechanisms largely presume threads. In our experience developing an operating system for embedded systems in Rust, we have found that Rust's ownership model prevents otherwise safe resource sharing common in the embedded domain, conflicts with the reality of hardware resources, and hinders using closures for programming asynchronously. We describe these experiences and how they relate to memory safety as well as illustrate our workarounds that preserve the safety guarantees to the largest extent possible. In addition, we draw from our experience to propose a new language extension to Rust that would enable it to provide better memory safety tools for event-driven platforms.

For the last fifteen years, research explored the hardware, software, sensing, communication abstractions, languages, and protocols that could make networks of small, embedded devices---motes---sample and report data for long periods of time unattended. Today, the application and technological landscapes have shifted, introducing new requirements and new capabilities. Hardware has evolved past 8 and 16 bit microcontrollers: there are now 32 bit processors with lower energy budgets and greater computing capability. New wireless link layers have emerged, creating protocols that support rapid and efficient setup and teardown but introduce novel limitations that systems must consider. The time has come to look beyond optimizing networks of motes. We look towards new technologies such as Bluetooth Low Energy, Cortex M processors, and capable energy harvesting, with new application spaces such as personal area networks, and new capabilities and requirements in security and privacy to inform contemporary hardware and software platforms. It is time for a new, open experimental platform in this post-mote era.