The concept of network on chip (NoC) is a recent breakthrough in the system on chip (SoC) design area. A lot of work has been done to define efficient NoC architectures and implementations. In this paper, our goal is twofold. Firstly, we want to outline that the use of a NoC based sharedmemory multiprocessor SoC challenges the application integrator because of the underlying assumptions of software, namely cache coherency and memory consistency. These problems are well known in general purpose shared memory multiprocessors. However, when designing a SoC, we benefit on the one hand from the knowledge of the applications, the much simpler usage of virtual memory, lower interconnect latencies and very high bandwidth at lost cost, but on the other hand we suffer from more tight design constraints (yield, power, predictable performances, ...). Secondly, we define simple and yet attractive solutions -in term of design time and hardware cost- to both problems in the context of application specific multiprocessor SoCs.

This paper presents Disydent, a framework dedicated to system-on-a-chip (SoC) platform-based design for shared memory multiple instructions multiple data (MIMD) architectures. We define a platform-based design problem as a triplet (system, application, constraints) where the system is both an operating system (OS) and a hardware (HW) template that can be enhanced with dedicated coprocessors. Our contributions are: 1) the definition of a complete flow for platform-based design, from application to integration including all necessary intermediate steps and 2) a set of tightly bound operational tools to implement the flow. Disydent is based on four tools. The distributed process network (DPN) is a C library for describing Kahn process network (KPN)-based applications. The asynchronous serial interface mode register 0 (ASIM0) is a multiprocessor target platform running a microkernel. This platform can be enhanced with coprocessors generated by the user-guided high-level synthesis (UGH) tool. Cycle accurate system simulator (CASS) is a high-performance cycle-accurate simulator. The main steps of the design flow are KPN modeling, functional validation, design space exploration, high-level synthesis, and temporal validation. The design flow starts by modeling the application as a KPN. This initial description is done in C using the DPN library. The functional validation is performed by running the initial description directly on the host. Without modifying the initial description, the user can simulate a HW/software (SW) partitioning by indicating the number of processors and the processes that are to be migrated to HW. This simulation is done at the cycle-accurate level for the whole system, except for the migrated processes for which the user must provide estimated time models. The description of the processes that are selected for HW implementation must be translated into a subset of C and then synthesized. This new description is still compatible with the DPN library, so it can be used for functional validation. The temporal validation is done at the cycle-accurate level using the initial description for the SW processes and cycle-accurate models automatically generated from the C subset description for the HW processes. Disydent's strength relies on its formal KPN model that ensures a behavior that is independent of the overall system scheduling, its fast cycle-accurate validation that is several orders of magnitude faster than classical event-driven simulators, and its single description of a process that is used as input of DPN, CASS, and UGH.