2. Specification and modeling

2.1 The heterogeneous nature of systems

The heterogeneous nature of systems-on-a-chip has already been briefly mentioned. In fact, it can be found at various levels within a system: software part (e.g. operating system) versus hardware part (e.g. processor and memory), data-oriented application algorithms versus control, hardware architecture composed of processors of the same type versus architecture combining processors and various hardware gas pedals (e.g. FPGA or GPU). All these characteristics require specification and modeling formalisms and approaches capable of capturing them fully. The following sections present an overview of these formalisms and approaches.