FlexACC: A Programmable Accelerator with Application-Specific ISA for Flexible Deep Neural Network Inference

Deep neural networks (DNN) have become ubiquitous and dominant in various application domains due to its state-of-the-art learning capabilities. To run compute and memory intensive DNN models, designing specialized hardware accelerators becomes the common choice. However, the performance improvement in accelerators comes with limitations on programmability, which has become crucial given the rapid evolution of DNN models. In this work, we first conduct workload analysis on a diverse set of DNN models, including CNN, LSTM, Transformer, and GCN to demonstrate the challenges of generalizing DNN acceleration. Next, we present a high-programmable accelerator, referred as FlexACC, with a novel application-specific ISA for flexible DNN inference. To increase the programmability, the general-purpose RISC-V instructions are tightly coupled with DNN instructions in FlexACC ISA. Compared with standalone fixed-datapath CNN and LSTM engines, FlexACC only has small latency and area overhead, while it provides much higher programmability and flexibility.