uSystolic: Byte-Crawling Unary Systolic Array

General matrix multiply (GEMM) is an important operation in broad applications, especially the thriving deep neural networks. To achieve low power consumption for GEMM, researchers have already leveraged unary computing, which manipulates bitstreams with extremely simple logic. However, existing unary architectures are not well generalizable to varying GEMM configurations in versatile applications and incompatible to the binary computing stack, imposing challenges to execute unary GEMM effortlessly. In this work, we address the problem by architecting a hybrid unary-binary systolic array, uSystolic, to inherit the legacy-binary data scheduling with slow (thus power-efficient) data movement, i.e., data bytes are crawling out from memory to drive uSystolic. uSystolic exhibits tremendous area and power improvements as a joint effect of 1) low-power computing kernel, 2) spatial-temporal bitstream reuse, and 3) on-chip SRAM elimination. For the evaluated edge computing scenario, compared with the binary parallel design, the rated-coded uSystolic reduces the systolic array area and total on-chip area by 59.0% and 91.3%, with the on-chip energy and power efficiency improved by up to 112.2× and 44.8× for AlexNet.