Abstract : AADL and MARTE are two modeling formalisms supporting the analysis of real-time embedded systems. Since both cover similar aspects, a clear assessment of their respective strength and weakness is required. Building on previous works, we focus here on the time aspects of the two specifications. Relying on the MARTE Time Model and the operational semantics of its companion language CCSL we attempt to equipped UML activities with the execution semantics of an AADL specification. This is part of a much broader effort to build a generic simulator for UML models with the semantics explicitly defined within the model.