Coarse-grained reconfigurable array architectures

Coarse-Grained Reconfigurable Array (CGRA) architectures accelerate the same inner loops that benefit from the high ILP support in VLIW architectures. By executing non-loop code on other cores, however, CGRAs can focus on such loops to execute them more efficiently. This chapter discusses the basic principles of CGRAs, and the wide range of design options available to a CGRA designer, covering a large number of existing CGRA designs. The impact of different options on flexibility, performance, and power-efficiency is discussed, as well as the need for compiler support. The ADRES CGRA design template is studied in more detail as a use case to illustrate the need for design space exploration, for compiler support and for the manual fine-tuning of source code

Pixie: A heterogeneous Virtual Coarse-Grained Reconfigurable Array for high performance image processing applications

Coarse-Grained Reconfigurable Arrays (CGRAs) enable ease of programmability and result in low development costs. They enable the ease of use specifically in reconfigurable computing applications. The smaller cost of compilation and reduced reconfiguration overhead enables them to become attractive platforms for accelerating high-performance computing applications such as image processing. The CGRAs are ASICs and therefore, expensive to produce. However, Field Programmable Gate Arrays (FPGAs) are relatively cheaper for low volume products but they are not so easily programmable. We combine best of both worlds by implementing a Virtual Coarse-Grained Reconfigurable Array (VCGRA) on FPGA. VCGRAs are a trade off between FPGA with large routing overheads and ASICs. In this perspective we present a novel heterogeneous Virtual Coarse-Grained Reconfigurable Array (VCGRA) called "Pixie" which is suitable for implementing high performance image processing applications. The proposed VCGRA contains generic processing elements and virtual channels that are described using the Hardware Description Language VHDL. Both elements have been optimized by using the parameterized configuration tool flow and result in a resource reduction of 24% for each processing elements and 82% for each virtual channels respectively.Comment: Presented at 3rd International Workshop on Overlay Architectures for FPGAs (OLAF 2017) arXiv:1704.0880

High throughput accelerator interface framework for a linear time-multiplexed FPGA overlay

Coarse-grained FPGA overlays improve design productivity through software-like programmability and fast compilation. However, the effectiveness of overlays as accelerators is dependent on suitable interface and programming integration into a typically processor-based computing system, an aspect which has often been neglected in evaluations of overlays. We explore the integration of a time-multiplexed FPGA overlay over a server-class PCI Express interface. We show how this integration can be optimised to maximise performance, and evaluate the area overhead. We also propose a user-friendly programming model for such an overlay accelerator system

Are coarse-grained overlays ready for general purpose application acceleration on FPGAs?

Combining processors with hardware accelerators has become a norm with systems-on-chip (SoCs) ever present in modern compute devices. Heterogeneous programmable system on chip platforms sometimes referred to as hybrid FPGAs, tightly couple general purpose processors with high performance reconfigurable fabrics, providing a more flexible alternative. We can now think of a software application with hardware accelerated portions that are reconfigured at runtime. While such ideas have been explored in the past, modern hybrid FPGAs are the first commercial platforms to enable this move to a more software oriented view, where reconfiguration enables hardware resources to be shared by multiple tasks in a bigger application. However, while the rapidly increasing logic density and more capable hard resources found in modern hybrid FPGA devices should make them widely deployable, they remain constrained within specialist application domains. This is due to both design productivity issues and a lack of suitable hardware abstraction to eliminate the need for working with platform-specific details, as server and desktop virtualization has done in a more general sense. To allow mainstream adoption of FPGA based accelerators in general purpose computing, there is a need to virtualize FPGAs and make them more accessible to application developers who are accustomed to software API abstractions and fast development cycles. In this paper, we discuss the role of overlay architectures in enabling general purpose FPGA application acceleration

A fully parameterized virtual coarse grained reconfigurable array for high performance computing applications

Field Programmable Gate Arrays (FPGAs) have proven their potential in accelerating High Performance Computing (HPC) Applications. Conventionally such accelerators predominantly use, FPGAs that contain fine-grained elements such as LookUp Tables (LUTs), Switch Blocks (SB) and Connection Blocks (CB) as basic programmable logic blocks. However, the conventional implementation suffers from high reconfiguration and development costs. In order to solve this problem, programmable logic components are defined at a virtual higher abstraction level. These components are called Processing Elements (PEs) and the group of PEs along with the inter-connection network form an architecture called a Virtual Coarse-Grained Reconfigurable Array (VCGRA). The abstraction helps to reconfigure the PEs faster at the intermediate level than at the lower-level of an FPGA. Conventional VCGRA implementations (built on top of the lower levels of the FPGA) use functional resources such as LUTs to establish required connections (intra-connect) within a PE. In this paper, we propose to use the parameterized reconfiguration technique to implement the intra-connections of each PE with the aim to reduce the FPGA resource utilization (LUTs). The technique is used to parameterize the intra-connections with parameters that only change their value infrequently (whenever a new VCGRA function has to be reconfigured) and that are implemented as constants. Since the design is optimized for these constants at every moment in time, this reduces the resource utilization. Further, interconnections (network between the multiple PEs) of the VCGRA grid can also be parameterized so that both the inter- and intraconnect network of the VCGRA grid can be mapped onto the physical switch blocks of the FPGA. For every change in parameter values a specialized bitstream is generated on the fly and the FPGA is reconfigured using the parameterized run-time reconfiguration technique. Our results show a drastic reduction in FPGA LUT resource utilization in the PE by at least 30% and in the intra-network of the PE by 31% when implementing an HPC application