Dynamic Partial Reconfiguration technology coupled with an Operating System for Reconfigurable Systems (OS4RS) allows for implementation of a hardware task concept, that is, an active computing object which can contend for reconfigurable computing resources and request OS services in a way software task does in a conventional OS. In this work, we show a complete model and implementation of a lightweight OS4RS supporting preemptable and clock-scalable hardware tasks. We also propose a novel, lightweight scheduling mechanism allowing for timely and priority-based reservation of reconfigurable resources, which aims at usage of preemption only at the time it brings benefits to the performance of a system. The architecture of the scheduler and the way it schedules allocations of the hardware tasks result in shorter latency of system calls, thereby reducing the overall OS overhead. Finally, we present a novel model and implementation of a channel-based intertask communication and synchronization suitable for software-hardware multitasking with preemptable and clock-scalable hardware tasks. It allows for optimizations of the communication on per task basis and utilizes point-to-point message passing rather than shared-memory communication, whenever it is possible. Extensive overhead tests of the OS4RS services as well as application speedup tests show efficiency of our approach. 1. Introduction The research on Dynamically Partially Reconfigurable (DPR) Field-Programmable Gate Arrays (FPGAs) is motivated by their superior flexibility, when compared to traditional FPGAs and Application-Specific Integrated Circuits (ASICs), as well as their potential to increase overall system performance and reduce dynamic power consumption by adapting to varying processing requirements of a system. DPR technology allows to partially change contents of the initial FPGA’s configuration at run-time, without disturbing operation of the rest of the system [1]. It leads to a concept of virtualization of hardware resources where a small, however, dynamically reconfigurable array, multiplexing its hardware resources in time, may give an illusion of hosting circuitry by far exceeding its real capacity [2]. While the idea of virtual hardware managed by an OS was first proposed by Brebner in [3, 4], Wigley and Karney [5] defined a set of properties an Operating System for Reconfigurable Systems (OS4RS) should have. These properties have been refined later on as the research in this field progressed [6]. The main objective of the OS4RS is to provide an abstraction layer boosting
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