Low-power embedded Internet system design

• Small mobile wireless sensors are used in many different areas, and they are expected to become even more common in the future as the miniaturisation of electronics continues. The current trend of connecting sensors into networks, or wireless sensor networks, is expected to continue and it has the potential to revolutionise our capability to monitor the physical world. To ensure communication compatibility and interoperability between sensors from different manufacturers within one sensor network, it is necessary to use standardised communication protocols. The most widespread network-independent protocol is IP, and we feel confident that IP will fill an important role in future sensor networks. For a number of reasons, including short development times and low development costs, a significant number of these systems are built using commercial-of-the-shelf (COTS) components. As development times and costs certainly will continue to be an issue which cannot be ignored, we believe that COTS components will be used in many future systems. Another issue is the power consumption: depending on the application area, the requirements on a system’s operational lifetime varies, but with few exceptions, low power consumption is a desired property. This thesis addresses the problem of designing low-power embedded internet systems (EIS) used in COTS-based sensor networks. A design methodology based on reactivity and analysability is presented. It is shown that a methodical choice of hardware components is not enough: thorough considerations regarding the software are also required. The purely reactive high-level language Timber is suggested as a suitable software model for implementing reactive and analysable systems. Timber’s strong type system, non-blocking execution model and implicit mutual exclusion, together with its capability to execute without an underlying operating system, endorse implementation of correct and robust systems. The deadline-based notion of Timber provides natural means to describe a system’s real-time behaviour. A method for automatic, accurate and safe static worst-case execution time (WCET) analysis of Timber is also presented. This is an important step towards schedulability analysis and low-power scheduling. Ultimately, reactive hardware together with a Timber-based software design methodology will relieve the system designer from the task of manual low-power optimisation.

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