Fine Grained Dynamically Reconfigurable Architecture (FGDRA) offers a flexibility for embedded systems with a great power processing efficiency by exploiting optimizations opportunities at architectural level thanks to their fine configuration granularity. But this increase design complexity that should be abstracted by tools and operating system. In order to have a usable solution, a good inter-overlapping between tools, OS, and platform must exist. In this paper we present OLLAF, an FGDRA specially designed to efficiently support an OS. The studies presented here show the contribution of this architecture in terms of hardware context management and preemption support. Studies presented here show the gain that can be obtained, by using OLLAF instead of a classical FPGA, in terms of context management and preemption overhead.