The Specification and Description Language (SDL) and its supporting CASE tools have a major potential for the development of real-time systems. Unfortunately, SDL does not capture either duration properties of computations or policies of pre-emptive scheduling which are commonly employed to coordinate the execution of multiple concurrent tasks. We propose an extension of SDL expressivity which can capture both the aspects through annotations in the body of comments of a standard SDL model. The annotated model, that we call modeling view can be automatically translated into a simulation view, still expressed in standard SDL, which can be composed with an SDL model of the real-time microkernel that is supposed to be employed in the target environment. Simulation of the composed model through any SDL tool reproduces a behavior which is compliant with timing and resource constraints expressed in the comments of the initial modeling view. This permits specification, documentation, and simulation of real time systems to be kept within the limits of standardized SDL capabilities.