Modern platform FPGAs integrate fine-grained reconfigurable logic with processor cores and allow the creation of complete configurable systems-on-chip. However, design methodologies have not kept up with the rise in complexity of the target hardware. In particular, there is little overlap between the programming model for embedded software running on a real-time operating system and the programming model for digital logic.In this paper, we present the operating system ReconOS which supports both software and hardware threads with a single unified programming model. ReconOS is based on eCos, a widely-used real-time operating system (RTOS). We investigate the incurred time and area overheads, especially for inter-thread communication across the hardware/-software boundary, and present a case study demonstrating the feasibility of the RTOS-centric design approach.