Over the course of the past decade, the evolution of advanced low-energy microcontrollers has raised three questions which this paper outlines and addresses.
The first question is: Can a 32-bit platform be constructed that provides advanced features but fits within the energy constraints of a wireless sensor network?
We answer this in the affirmative by presenting the design and preliminary evaluation of Storm – one such system based on an ARM Cortex-M4 that achieves 2.3µA idle current with a 1.5µS wake up time.
The second question we answer is: Can this platform simultaneously meet the very different demands of both monitoring-type applications and cyber-physical systems?
We demonstrate that this is indeed possible and present the design trade-offs that must be made to achieve this, yielding a module with a rich set of exported peripherals that fits in a 16mm x 26mm form factor.
The final question explored by this paper is: If such a platform is possible, what new opportunities and challenges would it hold for embedded operating systems?
We answer this by showing that the usage of modern 32 bit microcon- trollers requires reconsidering system architecture governing power management, clock selection and inter-module dependencies, as well as offering opportunities for supervisory code and the coordination of common tasks without CPU intervention. In particular, we address three basic questions:1. Can we now utilize full-featured, 32-bit microcon- trollers with enough memory and flash to support so- phisticated applications with the power profile of a mote, i.e., idle power of a few uWs, fast wake up, and efficient active operation?
2. Can the platform serve the distinct needs of the two dominant usage models: wireless monitoring, with a few sensors and predictable behavior and cyber- physical systems with rich I/O, actuation, and dynamic variation?
3. If so, does such a platform introduce qualitatively new operating system challenges and opportunities?
We show by developing a new platform around specific offerings in the Cortex-M family that the answer to the first two questions is affirmative and by examining aspects of this solution we outline a new suite of important system opportubities and challenges.
Indeed, the building blocks are finally of a state where the integration into a system-on-a-chip is likely to produce extremely general, cost-effective solutions.
Addressing the first question requires not just an analysis of data sheets; a quantitative, empirical study of the complex- ities and implications of utilizing next-generation hardware in sensor networks requires the careful design of a physical platform.
Storm is an example reference platform based upon best-in-class next-generation components. The process of mapping the model of a representative wireless embedded system into a physical instantiation by evaluation of available components and selective design trade-offs is discussed.
A physical module design is presented that extends and serves the range of usage models from simple sen-sor networks for monitoring to sophisticated cyber-physical systems.
The Storm platform is then used as a representative for next-generation wireless platforms in general for an exploration of new systems opportunities and challenges.
We identify five primary factors – modular power management, multiple clock domains, inter-module compatibility, chaining of multiple overlapping transfers and in creased supervisory control – which lead to a whole-system optimization framework for real time embedded operating systems, such as TinyOS.
Such intricacies naturally pose new problems for the architecture of any embedded operating system aiming to abstract device-specific complexity from users by utilizing layering and modularity.
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