ConvAix: An Application-Specific Instruction-Set Processor for the Efficient Acceleration of CNNs

IEEE Open Journal of Circuits and Systems, vol. 2, pp. 3–15

Abstract

ConvAix is an application-specific instruction-set processor (ASIP) that enables the energy-efficient processing of convolutional neural networks (CNNs) while retaining substantial flexibility through its instruction-set architecture (ISA) based design. By utilizing a combination of data-level parallelism (DLP), instruction-level parallelism (ILP), and subword parallelism, the proposed design offers sufficient processing power for the execution of state-of-the-art CNNs in real-time. ConvAix's arithmetic logic units (ALUs) are C-programmable, thereby offering the degree of flexibility required to implement many different convolution layer types, e.g., depthwise-separable convolutions and residual blocks, as well as fully-connected and pooling layers. It comprises a total of 256 ALUs and leverages low-precision computations down to 4 bits. Furthermore, it exploits sparsity in feature maps and weights via zero-guarding of redundant computations to maximize its energy efficiency. The processor was implemented in a modern 28 nm CMOS technology operating at 1V supply voltage with a resulting clock frequency of 513 MHz. The final design offers a precision-dependent peak throughput between 263 GOP/s (int16) and 1.1 TOP/s (int4), while consuming between 972mW and 340mW of power, resulting in effective energy-efficiencies ranging from 176 GOP/s/W to 2 TOP/s/W. Well-known CNNs, such as AlexNet, MobileNet, and ResNet-18, are simulated based on the placed and routed netlist, achieving between 233 (AlexNet) and 69 (ResNet-18) frames-per-second for a batch-size of 1, including times for off-chip transfers.

Authors 3

1. Andreas Bytyn Aachen Institute of Communication Technologies and Embedded Systems

   RWTH Aachen University

   Affiliation as printed

   Institute of Communication Technologies and Embedded Systems, RWTH Aachen University, Aachen, Germany

2. Rainer Leupers Aachen Institute of Communication Technologies and Embedded Systems

   RWTH Aachen University

   Affiliation as printed

   Institute of Communication Technologies and Embedded Systems, RWTH Aachen University, Aachen, Germany

3. Gerd Ascheid Aachen Institute of Communication Technologies and Embedded Systems

   RWTH Aachen University

   Affiliation as printed

   Institute of Communication Technologies and Embedded Systems, RWTH Aachen University, Aachen, Germany