This paper precent a new global MDA design methodology capable to bridge the gap between an abstract specification level and a heterogeneous architecture level while assisting real-time implementation. The P21 contribution is the result of a joint study on abstraction/refinement methods and optimized mapping on architecture within a UML based design tools suite including SCADE^TM Suite for formal verifications and SynDex for optimized distributed real- time implementation. The original points of this Mwk are: i) a specification methodology that handles the control flow and the data,flow representation, including efficient verifications, ii) a method jbr parallelism exploration bused on obstruct resoairces/Pei~tbriiiance estimtrtion iii) u HW/SW mapping approach that refines the specification into explicit WW configurations and the associated SW until executable distributed real-time code. The P21 framework shows how a cooperation qf complementary methodologies and CAD tools associated wifh a relevant architecture can significantly improve the designer productivity, especially in the context of co-modelling for Embedded Design.