In this paper a co-design methodology based on multifonnalism modelling is presented. It defines a platfonn that integrates different notations and, the necessary mechanisms to handle different in nature models in a coherent way. The supported fonnalisms cover a wide area of application domains, allowing the designer to select the notations that are mostly appropriate for his/her application. The proposed co-design development cycle provides a full blown path from system specification to a virtual prototype of the system under construction. The methodology has been applied for the design and implementation of a MAC layer protocol, named MASCARA, for providing A TM QoS over wireless connections.