Massively Parallel Multi-Processors System-on-Chip (MP2SoC) architectures require efficient programming models and tools to deal with the massive parallelism present within the architecture. In this paper, we propose a tool which automates the generation of the System-Level Architecture Model (S-LAM) from a Unified Modeling Language-based (UML) model annotated with the Modeling and Analysis of Real-Time and Embedded Systems (MARTE) profile. The S-LAM-based description of the MP2SoC architecture is conformed to the IP-XACT standard. The integration of our generator within a co-design framework provides the specification of the whole MP2SoC system using UML and MARTE. Then, gradual refinements allow the execution of a rapid prototyping process.