GigE vision data acquisition for visual servoing using SG/DMA proxying

Abstract

In many domains such as robotics and industrial automation, a growing number of Control Applications utilize cameras as a sensor. Such Visual Servoing Systems increasingly rely on Gigabit Ethernet (GigE) as a communication backbone and require real-time execution. The implementation on small, low-power embedded platforms suitable for the respective domain is challenging in terms of both computation and communication. Whilst advances in CPU and Field Programmable Gate Array (FPGA) technology enable the implementation of computationally heavier Image Processing Pipelines, the interface between such platforms and an Ethernet-based communication backbone still requires careful design to achieve fast and deterministic Image Acquisition. Although standardized Ethernet-based camera protocols such as GigE Vision unify camera configuration and data transmission, traditional software-based Image Acquisition is insufficient on small, low-power embedded platforms due to tight throughput and latency constraints and the overhead caused by decoding such multi-layered protocols. In this paper, we propose Scatter-Gather Direct Memory Access (SG/DMA) Proxying as a generic method to seamlessly extend the existing network subsystem of current Systemson- Chip (SoCs) with hardware-based filtering capabilities. Based thereon, we present a novel mixed-hardcore/softcore GigE Vision Framegrabber capable of directly feeding a subsequent in-stream Image Processing Pipeline with sub-microsecond acquisition latency. By rerouting all incoming Ethernet frames to our GigE Vision Bridge using SG/DMA Proxying, we are able to separate image and non-image data with zero CPU and memory intervention and perform Image Acquisition at full line rate of Gigabit Ethernet (i.e., 125 Mpx/s for grayscale video). Our experimental evaluation shows the benefits of our proposed architecture on a Programmable SoC (pSoC) that combines a fixed-function multi-core SoC with configurable FPGA fabric.