This paper provides an overview of some principles and mechanisms to securely operate mixed-criticality real-time systems on embedded platforms. Those principles are illustrated with PharOS, a complete set of tools to design, implement and execute real-time systems on automotive embedded platforms.The keystone of this approach is a dynamic time-triggered methodology that supports full temporal isolation without wasting CPU time. In addition, memory isolation is handled through automatic off-line generation of fine-grained memory protection tables used at runtime. These isolation mechanisms are building blocks for the support of mixed-criticality applications. Several extensions have been brought to this model to expand the support for mixed-criticality within the system. These extensions feature fault recovery, support for the cohabitation of eventtriggered with time-triggered tasks and paravirtualization of other operating systems. The contribution of this paper is to provide a high-level description of these extensions, along with an analysis of their impact on the global system safety, in particular on the determinism property of the PharOS model.

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