"Design of a Reusable SpaceWire Link Interface for Space Avionics and Instrumentation"

Mark A. Johnson, Buddy Walls, Kristian Persson, Sandra G. Dykes
Southwest Research Institute


SpaceWire is an emerging network protocol designed to expand on-board spacecraft communications through use of a multi-hop, switched network architecture, supporting data rates from 2Mbps to 400Mbps. Based initially on IEEE 1355-1995, the electrical interface has been optimized for the rigors of spacecraft operations and adopted as standard ECSS-E-50-12A by ESA. With recent standardization of the protocol, attention can now be focused on development of SpaceWire hardware, including interface cards and network routers. This paper describes our approach and technical developments to provide radiation hardened SpaceWire solutions using the high performance CompactPCI (cPCI) bus. Driven by a combination of increasing mission throughput and aggressive processing requirements, the choice of the cPCI bus has fueled development of a new generation of SpaceWire hardware for space applications.

SpaceWire is part of a new and exciting area of spacecraft command and data handling research: the creation of a Local Area Network (LAN) as the backbone for intra-spacecraft data communication. SpaceWire links provide a high reliability data layer and a sufficiently robust network layer for seamless spacecraft data communications. Moreover, on-board nodes can run IP protocols over SpaceWire. From the IP layer point of view, a multi-hop SpaceWire network path appears as a single IP link. This network layer approach allows spacecraft software to leverage the extensive and mature set of IP protocols, software, and hardware for data collection and distribution. Benefits include lower costs due to COTS availability, reduced integration and testing efforts, and access to an unparalleled knowledge base. For both immediate use in current on-board SpaceWire networks and to facilitate our research into hosting IP on these networks, we have developed a full duplex SpaceWire Link Interface Module (SLIM) interfacing on a 3U cPCI card. Our implementation incorporates two independent 64Kbyte FIFOs for SpaceWire link transmit and receive, a single SpaceWire link interface providing exchange level protocol support, and a programmable
interrupt controller, interfacing with the cPCI Bus. A SwRI-developed cPCI target core was employed to provide increased transaction throughput tailored to the high bandwidth capabilities of the SpaceWire bus.

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