System level synthesis is widely seen as the solution for closing the productivity gap in system design. High level system models are used in system level design for early design exploration. While real time operating systems (RTOS) are an increasingly important component in system design, specific RTOS implementations can not be used directly in high level models. On the other hand, existing system level design languages (SLDL) lack support for RTOS modeling. In this paper we propose a RTOS model built on top of existing SLDLs which, by providing the key features typically available in any RTOS, allows the designer to model the dynamic behavior of multi-tasking systems at higher abstraction levels to be incorporated into existing design flows. Experimental result shows that our RTOS model is easy to use and efficient while being able to provide accurate results.