EMERALDS (Extensible Microkernel for Embedded, ReAL-time, Distributed Systems) is a real-time microkernel designed for small-memory embedded applications. These applications must run on slow (15-25MHz) processors with just 32-128 kbytes of memory, either to keep production costs down in mass-produced systems or to keep weight and power consumption low. To be feasible for such applications, the OS must not only be small in size (less than 20 kbytes), but also have low-overhead kernel services. Unlike commercial embedded OSs which rely on carefully-crafted code to achieve efficiency, EMERALDS takes the approach of re-designing the basis OS services of task scheduling, synchronization, communication, and system call mechanism by using characteristics found in small-memory embedded systems, such as small code size and a priori knowledge of task execution and communication patterns. With these new schemes, the overheads of various OS services are reduced 20-40% without compromising any OS functionality.
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