Today, having a fast hardware platform for SoC software development prior to silicon is an important challenge to gain the time-to-market. The FPGAs offer an excellent prototyping basis for building hardware platforms since more than ten years ([1]). However, as the circuit complexity increases and project time-frames shrink, building a multi-FPGA prototype represents a real challenge from the complexity viewpoint. The paper describes the state-of-the-art mapping methodology, prototyping tools and flows, shows the most difficult mapping problems and the ways to overcome them. The paper is issued from the experience of mapping on FPGA platform of four latest highly complex ST Microelectronics SoCs ranging from 1.5 to 4 million real ASIC gates mapped to up to 9 highest capacity FPGAs.