A CycleGAN Accelerator for Unsupervised Learning on Mobile Devices

Cycle-consistent generative adversarial networks (CycleGANs) have been commonly used for unsupervised-learning applications, especially for image-to-image translation. A CycleGAN has more complex dataflow since it features two generator-discriminator pairs. Massive external memory access also results in a long latency for both training and inference. Data structure for transposed convolution also needs to be tailored. This paper presents the first dedicated CycleGAN accelerator for energy-constrained mobile applications. The numbers of external and internal memory accesses are reduced by 98.3% and 68.3% through spatial data reuse, input feature map reuse, and local data reuse. The computational complexity is reduced by 79.4% by skipping zeros in the transposed convolutional layers. An architecture with two processing cores is proposed to improve the utilization by 2×. Designed in a 40-nm CMOS technology, the proposed CycleGAN accelerator dissipates 445 mW at 227 MHz from a 0.9-V supply. It achieves a 38× higher throughput-to-area ratio and 127× higher energy efficiency than a GPU.