Implementing Wireless Sensor Network Applications using Hierarchical Finite State Machines

In typical application scenarios of wireless sensor systems the embedded software follows a sequential program-flow. Such sequential systems are easily described using a finite state machine (FSM) abstraction model, as it is known from digital circuit design and control system development. In practice, a theoretical description in the form of an FSM must be transferred into a software implementation using an efficient programming abstraction method. This paper presents the implementation of a lightweight software library, which supports the development of wireless sensor applications based on hierarchical finite state machines (HFSM). With its minimalistic design approach, the implementation creates a small memory footprint and a high efficiency in state transitions and in Interrupt Service Routine execution. By introducing a hierarchical state machine architecture it is possible to split a complex algorithm into sub-modules. Hence, the code modularity and reusability is improved. Moreover, it is possible to test each module independently, so that code errors can be traced back more rapidly. This results in a very reliable application software.