DRA: Ultra-Low Latency Network I/O for TSN Embedded End-Systems.

Time-Sensitive Networking (TSN) is a promising open-source technique for hard real-time embedded fields such as industrial automation and autonomous driving. The embedded end-system deployed in TSN must guarantee deterministic latency and jitter for network I/O in above scenarios. Recent researchers focus on eliminating jitter but neglect to reduce latency. The network I/O latency is still too high to satisfy the dozen-microsecond requirements of latency-sensitive applications. We observed that (1) the data path from registers to external storage is actually the bottleneck for latency reduction, and (2) the serial processing of CPU and NIC can be further optimized. Therefore, we proposed DRA (Direct Register Access), a novel network I/O mechanism to achieve microsecond-level latency. DRA delivers whole packet data from the NIC directly into extended registers inside the CPU, avoiding the waste of time to move data between internal registers and external storage. Moreover, DRA promotes parallelization of CPU processing and NIC transfer to reduce latency. Considering the increasing popularity of RISC-V ISA in embedded systems, we prototype DRA using an open-source RISC-V core on FPGA and evaluate it under real-life application scenarios. Compared with existing mechanisms, experimental results demonstrate that DRA reduces the network I/O latency and jitter by at least 60% and 30%, achieving microsecond-level network I/O processing.