The functionality of embedded systems is ever increasing. This has lead to mixed time-criticality systems, where applications with a variety of real-time requirements co-exist on the same platform and share resources. Due to inter-application interference, verifying the real-time requirements of such systems is generally non trivial. In this paper, the authors present the CoMik microkernel that provides temporally predictable and composable processor virtualization. CoMik's virtual processors are cycle-accurately composable, i.e. their timing cannot affect the timing of co-existing virtual processors by even a single cycle.