Spiking Neural Network (SNN) inference has a clear potential for high energy efficiency as computation is triggered by events. However, the inherent sparsity of events poses challenges for conventional computing systems, driving the development of specialized neuromorphic processors, which come with high silicon area costs and lack the flexibility needed for running other computational kernels, limiting widespread adoption. In this paper, we explore the low-level software design, parallelization, and acceleration of SNNs on general-purpose multicore clusters with a low-overhead RISC-V ISA extension for streaming sparse computations. We propose SpikeStream, an optimization technique that maps weights accesses to affine and indirect register-mapped memory streams to enhance performance, utilization, and efficiency. Our results on the end-to-end Spiking-VGG11 model demonstrate a significant 4.39× speedup and an increase in utilization from 9.28% to 52.3 % compared to a non-streaming parallel baseline. Additionally, we achieve an energy efficiency gain of 3.46× over LSMCore and a performance gain of 2.38× over Loihi.

End-to-end open-source electronic design automation enables a collaborative approach to chip design conducive to supply chain diversification and zero-trust step-by-step design verification. However, existing end-to-end OSEDA flows have mostly been demonstrated on small designs and have not yet enabled large, industry-grade chips such as Linux-capable systems-on-chip (SoCs). This work presents Basilisk, the largest end-to-end open-source SoC to date. Basilisk’s 34mm2, 2.7MGE design features a 64-bit Linuxcapable RISC-V core, a lightweight 124MB/s DRAM controller, and extensive IO, including a USB 1.1 host, a video output, and a fully digital 62Mb/s chip-to-chip (C2C) link. We implement Basilisk in IHP’s open 130nm BiCMOS technology, significantly improving on the state-of-the-art (SoA) OSEDA flow. Our enhancements of the Yosys-based synthesis flow improve design timing and area by 2.3×and 1.6×, respectively, while consuming significantly less system resources. By tuning OpenROAD place and route (P&R) to our design and technology, we decrease the die size by 12%. The fabricated Basilisk chip reaches 62MHz at its nominal 1.2V core voltage and up to 102MHz at 1.64V. It achieves a peak energy efficiency of 18.9DPMFLOP/s/W at 0.88V.

Stencil codes are performance-critical in many compute-intensive applications, but suffer from significant address calculation and irregular memory access overheads. This work presents SARIS, a general and highly flexible methodology for stencil acceleration using register-mapped indirect streams. We demonstrate SARIS for various stencil codes on an eight-core RISC-V compute cluster with indirect stream registers, achieving significant speedups of 2.72x, near-ideal FPU utilizations of 81%, and energy efficiency improvements of 1.58x over an RV32G baseline on average. Scaling out to a 256-core manycore system, we estimate an average FPU utilization of 64%, an average speedup of 2.14x, and up to 15% higher fractions of peak compute than a leading GPU code generator.

Sparse matrix-vector multiplication (SpMV) is central to numerous data-intensive applications, but requires streaming indirect memory accesses that severely degrade both processing and memory throughput in state-of-the-art architectures. Near-memory hardware units, decoupling indirect streams from processing elements, partially alleviate the bottleneck, but rely on low DRAM access granularity, which is highly inefficient for modern DRAM standards like HBM and LPDDR. To fully address the end-to-end challenge, we propose a low-overhead data coa- lescer combined with a near-memory indirect streaming unit for AXI-Pack, an extension to the widespread AXI4 protocol packing narrow irregular stream elements onto wide memory buses. Our combined solution leverages the memory-level parallelism and coalescence of streaming indirect accesses in irregular applications like SpMV to maximize the performance and bandwidth efficiency attained on wide memory interfaces. Our solution delivers an average speedup of 8x in effective indirect access, often reaching the full memory bandwidth. As a result, we achieve an average end-to-end speedup on SpMV of 3x. Moreover, our approach demonstrates remarkable on-chip efficiency, requiring merely 27kB of on-chip storage and a very compact implementation area of O.2-0.3mm2in a 12nm node.

Data transfers are essential in today's computing systems as latency and complex memory access patterns are increasingly challenging to manage. Direct memory access engines (DMAES) are critically needed to transfer data independently of the processing elements, hiding latency and achieving high throughput even for complex access patterns to high-latency memory. With the prevalence of heterogeneous systems, DMAEs must operate efficiently in increasingly diverse environments. This work proposes a modular and highly configurable open-source DMAE architecture called intelligent DMA (iDMA), split into three parts that can be composed and customized independently. The front-end implements the control plane binding to the surrounding system. The mid-end accelerates complex data transfer patterns such as multi-dimensional transfers, scattering, or gathering. The back-end interfaces with the on-chip communication fabric (data plane). We assess the efficiency of iDMA in various instantiations: In high-performance systems, we achieve speedups of up to 15.8$\boldsymbol{\times}$with only 1% additional area compared to a base system without a DMAE. We achieve an area reduction of 10% while improving ML inference performance by 23% in ultra-low-energy edge AI systems over an existing DMAE solution. We provide area, timing, latency, and performance characterization to guide its instantiation in various systems.

Data-intensive applications involving irregular memory streams are inefficiently handled by modern processors and memory systems highly optimized for regular, contiguous data. Recent work tackles these inefficiencies in hardware through core-side stream extensions or memory-side prefetchers and accelerators, but fails to provide end-to-end solutions which also achieve high efficiency in on-chip interconnects. We propose AXI-Pack, an extension to ARM's AXI4 protocol introducing bandwidth-efficient strided and indirect bursts to enable end-to-end irregular streams. AXI-Pack adds irregular stream semantics to memory requests and avoids inefficient narrow-bus transfers by packing multiple narrow data elements onto a wide bus. It retains full compatibility with AXI4 and does not require modifications to non-burst-reshaping interconnect IPs. To demonstrate our approach end-to-end, we extend an open-source RISC-V vector processor to leverage AXI-Pack at its memory interface for strided and indexed accesses. On the memory side, we design a banked memory controller efficiently handling AXI-Pack requests. On a system with a 256-bit-wide interconnect running FP32 workloads, AXI-Pack achieves near-ideal peak on-chip bus utilizations of 87% and 39%, speedups of 5.4x and 2.4x, and energy efficiency improvements of 5.3x and 2.1x over a baseline using an AXI4 bus on strided and indirect benchmarks, respectively.

Sparse linear algebra is crucial in many application domains, but challenging to handle efficiently in both software and hardware, with one- and two-sided operand sparsity handled with distinct approaches. In this work, we enhance an existing memory-streaming RISC-V ISA extension to accelerate both one- and two-sided operand sparsity on widespread sparse tensor formats like compressed sparse row (CSR) and compressed sparse fiber (CSF) by accelerating the underlying operations of streaming indirection, intersection, and union. Our extensions enable single-core speedups over an optimized RISC-V baseline of up to 7.0x, 7.7x, and 9.8x on sparse-dense multiply, sparse-sparse multiply, and sparse-sparse addition, respectively, and peak FPU utilizations of up to 80% on sparse-dense problems. On an eight-core cluster, sparse-dense and sparse-sparse matrix-vector multiply using real-world matrices are up to 4.9x and 5.9x faster and up to 2.9x and 3.0x more energy efficient. We explore further applications for our extensions, such as stencil codes and graph pattern matching. Compared to recent CPU, GPU, and accelerator approaches, our extensions enable higher flexibility on data representation, degree of sparsity, and dataflow at a minimal hardware footprint, adding only 1.8% in area to a compute cluster. A cluster with our extensions running CSR matrix-vector multiplication achieves 9.9x and 1.7x higher peak floating-point utilizations than recent highly optimized sparse data structures and libraries for CPU and GPU, respectively, even when accounting for off-chip main memory (HBM) and on-chip interconnect latency and bandwidth effects.

Sparse-dense linear algebra is crucial in many domains, but challenging to handle efficiently on CPUs, GPUs, and accelerators alike; multiplications with sparse formats like CSR and CSF require indirect memory lookups. In this work, we enhance a memory-streaming RISC-V ISA extension to accelerate sparse-dense products through streaming indirection. We present efficient dot, matrix-vector, and matrix-matrix product kernels using our hardware, enabling single-core FPU utilizations of up to 80% and speedups of up to 7.2x over an optimized baseline without extensions. A matrix-vector implementation on a multicore cluster is up to 5.8x faster and 2.7x more energy-efficient with our kernels than an optimized baseline. We propose further uses for our indirection hardware, such as scatter-gather operations and codebook decoding, and compare our work to state-of-the-art CPU, GPU, and accelerator approaches, measuring a 2.8x higher peak FP64 utilization in CSR matrix-vector multiplication than a GTX 1080 Ti GPU running a cuSPARSE kernel.

System simulators are essential for the exploration, evaluation, and verification of manycore processors and are vital for writing software and developing programming models in conjunction with architecture design. A promising approach to fast, scalable, and instruction-accurate simulation is binary translation. In this paper, we present Banshee, an instruction-accurate full-system RISC-V multi-core simulator based on LLVM-powered ahead-of-time binary translation that can simulate systems with thousands of cores. Banshee supports the RV32IMAFD instruction set. It also models peripherals, custom ISA extensions, and a multi-level, actively-managed memory hierarchy used in existing multi-cluster systems. Banshee is agnostic to the host architecture, fully open-source, and easily extensible to facilitate the exploration and evaluation of new ISA extensions. As a key novelty with respect to existing binary translation approaches, Banshee supports performance estimation through a lightweight extension, modeling the effect of architectural latencies with an average deviation of only 2 % from their actual impact. We evaluate Banshee by simulating various compute-intensive workloads on two large-scale open-source RISC-V manycore systems, Manticore and MemPool (with 4096 and 256 cores, respectively). We achieve simulation speeds of up to 618 MIPS per core or 72 GIPS for complete systems, exhibiting almost perfect scaling, competitive single-core performance, and leading multi-core performance. We demonstrate Banshee's extensibility by implementing multiple custom RISC-V ISA extensions.