Among solutions to allow sub-millisecond determinism for real-time Linux applications, the co-kernel approach is found in many products and is probably to most widely known — and used — technique. In the past few years, this approach evolved, at least in the RTAI project, towards a better integration of the co-kernel deterministic services to Linux:

• the co-kernel interfaces were brought to… user-space, allowing real-time applications to run under memory protection;
• any thread was allowed to use alternatively the two interfaces, suppressing the need for splitting the application into a Linux-based and real-time parts and for communication facilities between these two parts.

In this paper, we describe a versatile software architecture which, in our view, is the next step towards the seamless integration of real-time to the Linux user-space. Based on the Adeos technology, it improves:

• the determinism of a real-time task calling Linux services, by preventing events of lower priority from causing any disturbance;
• the integration of the two application programming interfaces, by redirecting Linux system calls to their real-time counterpart.

We present the mechanisms used to achieve these goals and that are included in a deterministic intensive computing (DIC) domain: interrupt dispatch control, thread management, services integration, system call handling mechanism. The integration of these real-time services in the POSIX API is also discussed. Finally, performance results for different architectures are presented.

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