EMERALDS: A small-memory real-time microkernel

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