Reconfigurable Systems-on-Chip (SoC) on the market consists of full-edged processors and large Field-Programmable Gate-Arrays (FPGAs). The latter can be used to implement the system glue logic, various peripherals, and application-specific coprocessors. Using FPGAs for application-specific coprocessors has certain speed up potentials, but it is less frequent in practice because of the complexity of interfacing the software application with the coprocessor. Another obstacle is the lack of portability across different systems. In this paper, the authors present a virtualization layer consisting of an operating-system extension and a hardware component.