Validating Hybrid Designs with Co-Simulation

It is generally accepted that simulation is beneficial to the validation phase of systems development. When hybrid system specifications are concerned co-simulation is required. In the INSYDE project co-simulation is accomplished using two commercial simulators. This paper concentrates on the chosen co-simulation approach with a strong emphasis on the problem of synchronisation. We present solutions to this problem for the telecommunications case study that was completed in the project. THE INSYDE METHODOLOGY INSYDE (Integrated methods for evolving systems design) is an EU funded ESPRIT III project. Main objective of the project is to define, implement, validate and demonstrate a comprehensive methodology for hybrid systems design. Hybrid systems are systems consisting of software and hardware. The result of the project is a prototype methodology and toolset combining the advantages of Object-Orientation and Formal Description Techniques (for both hardware and software design) and covering a fully integrated development cycle. Stages in the INSYDE Methodology are analysis, de ign and validation. The major goal of the analysis phase is to get a thorough understanding of the system under development. Analysis culminates in a Conceptual Model. This is specified using OMT, the Object Modelling Technique (Rumbaugh et al. 1991). The Design phase of the INSYDE Methodology can be divided in System Design and Detailed Design. System Design is concerned with the specification of subsystems and the interactions between them. These subsystems can be hardware or software. The OMT Conceptual Model is the basis for System Design. The System Design phase results in a System Design Model, which serves as a starting point for Detailed Design. The System Design Model is specified in OMT* (Jonckers et al. 1995). The transformation of the OMT model into a OMT* model is done manually. Detailed Design deals with hardware and software subsystems separately. The languages for detailed design are SDL’88 (CCITT 1988), SDL’92 (Faergemand et al. 1994) and VHDL (ANSI/IEEE 1993). By means of SDL ( Specification and Description Language ), it is possible to describe both the structure of a system and the system behaviour on different levels of abstraction. The behaviour description is based on the concept of extended finite state machines communicating asynchronously by message exchange. VHDL (Very High Speed Integrated Circuit Hardware Description Language ) is a technique for the design and description of hardware systems. The language supports hierarchical descriptions of hardware from system to gate or even switch level. For development and simulation of the specifications two commercial packages are used. For the SDL side the GEODE toolset from Verilog is used and for VHDL the Leapfrog (Cadence) environment is taken. The transformation of the OMT* descriptions into SDL/VHDL is done by software tools as automatically as possible, with human intervention where appropriate. The transformation results in a system description consisting of parts described in SDL and parts described in VHDL. The hybrid system specification can be refined or modified following the general guidelines for SDL and VHDL. The method chosen for the validation of hybrid SDL and VHDL specifications is Co-Simulation. The introduced methodology is demonstrated in the INSYDE project with two case studies: an Interactive Video-on-Demand (IVoD) system, made by Alcatel Bell (Belgium) and an Image Reconstruction system, made by Intracom (Greece). The results from the first case study are used in this paper.