New applications introducing restrictions in power consumption, heat, costs and available space lead to small microcontrollers becoming more and more important in distributed real-time systems. Traditional real-time middleware architectures don't fit very well for these small devices. The paper presents an ongoing approach of constructing middleware for small devices by adapting the microkernel concept known from operating systems to middleware. This middleware called OSA+ is service oriented and consists of a small core, basic-, extension-, and user-services. The core provides only a restricted functionality, while the basic and extension services adapt and scale the system according to the application environment. A first (quick and non-optimal) prototype implementation offers a core size of about 60 kBytes and an average size of about 10 kBytes for a basic service. We consider this as a basis for further optimizations leading to yet smaller sizes.
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