A real-time kernel for wireless sensor networks employed in rescue scenarios

In rescue scenarios, real-time requirements are one key issue when using wireless sensor networks (WSNs) for tracking and monitoring of rescue forces. If a node detects an alarm condition, the alarm message must be delivered to the base station in time. To guarantee the timely delivery the whole system architecture has to fulfill real-time requirements. There are only a few real-time architectures which can be used for sensor networks. These architectures are too generic to comply with the other requirements of a WSN architecture, like RAM usage and energy awareness. In this paper, we present FireKernel, a real-time micro kernel designed for WSN operating systems with a special focus on hard real-time requirements and strict energy management. It offers a preemptive real-time scheduler, mutexes and synchronous message passing for interprocess communication (IPC). The scheduler is prioritybased and uses no periodical timers. As part of the kernel we introduce a tickless timer system. We have implemented and tested the kernel on MSP430 and ARM7TDMI based sensor nodes. We discuss the kernel´s architecture, implementation and resource usage. Further, we present benchmark results for interrupt latency and energy consumption of the timer architecture.