In this paper, we describe our methodology for cosimulation at a high level of abstraction, to validate the execution of real time applications on simulated H/W, using a simulation wrapper of a real time operating system (RTOS). The simulation wrapper is built on kernel target specification described in a kernel framework model (KFM), by adding the constructs needed for simulation dynamics to create a simulation model of an RTOS. We describe these dynamics and then show the interaction of the embedded S/W consisting of the simulation model of the RTOS and the application running above, with a bus functional model (BFM) of a micro-controller. Our methodology is demonstrated by S/W application.