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Electronic Design

TinyOS Plus ZigBee Stack Targets Tiny Tasks

TinyOS is a compact operating system (OS) designed to support small wireless platforms like 8-bit ZigBeebased microcontroller solutions. It's an open-source project that was first developed at U.C. Berkeley by the likes of David Culler, now chairman, co-founder, and CTO of Arch Rock. The company announced its ZigBee support at the 2006 Sensors and Expo Conference in Chicago, where the company also showed off its TinyOS 2.0. Arch Rock also supports a range of wireless solutions including support for IEEE 802.15.4 and IEEE 802.11.

TinyOS can be used as a general OS, but it targets wireless sensing mesh networks that incorporate thousands of devices. The concept is also called smartdust, and the devices are often referred to as motes. The idea is that motes would be so inexpensive that they could be embedded everywhere, providing details such as stress information within a build-ing s structure. TinyOS already runs on a range of processors, including ARM processors and DSPs.

TinyOS is designed to be simple but flexible. Its default scheduler has a non-preemptive FIFO policy. The system supports commands (function calls) and events (callback functions). A close relationship with the hardware can be had with a split-phase approach where a command starts an operation and an event is used for complete it.

Functions are divided into synchronous (sync) and asynchronous (async) groups. Async functions can only call other async functions. Events are always sync.

Another major difference compared to other platforms is that applications are built from components that are designed to be wired together with connections between component interfaces. Wiring can be parameterized or combined. Pass-through wiring allows efficient implementation of shims.

Interestingly, the environment uses only local namespaces instead of the global namespace normally found in Java or C++. A local namespace means the developer must define functions that are called via an interface, as well as functions that will be exported by the application through its interfaces.

A new programming language called nesC was developed to build TinyOS and its applications. It is a variant of C that implements the TinyOS concurrency model and interfaces. Tools like ncc, the nesC compiler, are available on most PC platforms such as Windows and Linux.

Two items often found on a TinyOS system are TinyDB and Maté. TinyDB is a compact, distributed database that runs on TinyOS. Maté is a virtual machine with a Forth-like architecture that runs capsules, which are small collections of byte codes. Applications can consist of one or more capsules. Capsules are easy to broadcast through a mesh network because of their small size.

The chips and OS may be tiny, but they may have huge implications for the future.

TAGS: Digital ICs
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