Worst-case latency analysis for the versal NoC network packet switch

Abstract

The recent line of Versal FPGA devices from Xilinx Inc. includes a hard Network-On-Chip (NoC) embedded in the programmable logic, designed to be a high-performance system-level interconnect. While the target markets for Versal devices include applications with real-time constraints, such as automotive driver assist, the associated development tools only provide figures for "structural latencies"of data packets, which assume that the network is otherwise idle. In a realistic setting, this information is not enough to ensure deadlines are met, as different packets can contend for NoC switch outputs, which causes packet contents to be buffered while in transit, increasing their latency. In this work, we present a formal description of the NPS switches that compose the Versal NoC from a flit (or packet) scheduling perspective, based on the available cycle-accurate switch simulation code. We then analyze a scenario where network clients transfer data periodically over a single switch, and propose a method for calculating worst-case communication times in this scenario.