HERO: Heterogeneous Embedded Research Platform for Exploring RISC-V Manycore Accelerators on FPGA

Heterogeneous embedded systems on chip (HESoCs) co-integrate a standard host processor with programmable manycore accelerators (PMCAs) to combine general-purpose computing with domain-specific, efficient processing capabilities. While leading companies successfully advance their HESoC products, research lags behind due to the challenges of building a prototyping platform that unites an industry-standard host processor with an open research PMCA architecture. In this work we introduce HERO, an FPGA-based research platform that combines a PMCA composed of clusters of RISC-V cores, implemented as soft cores on an FPGA fabric, with a hard ARM Cortex-A multicore host processor. The PMCA architecture mapped on the FPGA is silicon-proven, scalable, configurable, and fully modifiable. HERO includes a complete software stack that consists of a heterogeneous cross-compilation toolchain with support for OpenMP accelerator programming, a Linux driver, and runtime libraries for both host and PMCA. HERO is designed to facilitate rapid exploration on all software and hardware layers: run-time behavior can be accurately analyzed by tracing events, and modifications can be validated through fully automated hard ware and software builds and executed tests. We demonstrate the usefulness of HERO by means of case studies from our research

Handling large data sets for high-performance embedded applications in heterogeneous systems-on-chip

Local memory is a key factor for the performance of accelerators in SoCs. Despite technology scaling, the gap between on-chip storage and memory footprint of embedded applications keeps widening. We present a solution to preserve the speedup of accelerators when scaling from small to large data sets. Combining specialized DMA and address translation with a software layer in Linux, our design is transparent to user applications and broadly applicable to any class of SoCs hosting high-throughput accelerators. We demonstrate the robustness of our design across many heterogeneous workload scenarios and memory allocation policies with FPGA-based SoC prototypes featuring twelve concurrent accelerators accessing up to 768MB out of 1GB-addressable DRAM

Lightweight virtual memory support for many-core accelerators in heterogeneous embedded SoCs

While high-end heterogeneous systems are increasingly supporting heterogeneous uniform memory access (hUMA) as envisioned by the Heterogeneous System Architecture (HSA) foundation, their low-power counterparts targeting the embedded domain still lack basic features like virtual memory support for accelerators. As opposed to simply passing virtual address pointers, explicit data management involving copies is needed to share data between host processor and accelerators which hampers programmability and performance. In this work, we present a mixed hardware/software solution to enable lightweight virtual memory support for many-core accelerators in heterogeneous embedded systems-on-chip (SoCs). Based on an input/output translation lookaside buffer (IOTLB), efficiently managed by a kernel-level driver module running on the host, our solution features a considerably lower design complexity compared to conventional input/output memory management units. Using our evaluation platform based on the Xilinx Zynq-7000 SoC with a many-core accelerator implemented in the programmable logic, we demonstrate the effectiveness of our solution and the benefits of virtual memory support for embedded heterogeneous SoCs

Generation of Application Specific Hardware Extensions for Hybrid Architectures: The Development of PIRANHA - A GCC Plugin for High-Level-Synthesis

Architectures combining a field programmable gate array (FPGA) and a general-purpose processor on a single chip became increasingly popular in recent years. On the one hand, such hybrid architectures facilitate the use of application specific hardware accelerators that improve the performance of the software on the host processor. On the other hand, it obliges system designers to handle the whole process of hardware/software co-design. The complexity of this process is still one of the main reasons, that hinders the widespread use of hybrid architectures. Thus, an automated process that aids programmers with the hardware/software partitioning and the generation of application specific accelerators is an important issue. The method presented in this thesis neither requires restrictions of the used high-level-language nor special source code annotations. Usually, this is an entry barrier for programmers without deeper understanding of the underlying hardware platform. This thesis introduces a seamless programming flow that allows generating hardware accelerators for unrestricted, legacy C code. The implementation consists of a GCC plugin that automatically identifies application hot-spots and generates hardware accelerators accordingly. Apart from the accelerator implementation in a hardware description language, the compiler plugin provides the generation of a host processor interfaces and, if necessary, a prototypical integration with the host operating system. An evaluation with typical embedded applications shows general benefits of the approach, but also reveals limiting factors that hamper possible performance improvements