Adaptation Layer for SpaceWire Plug and Play Protocols, 10-R8216
Inclusive Dates: 04/01/11 – 09/30/12
Background — Two plug and play (PnP) protocol options for SpaceWire (SpW) exist – one defined by the U.S. Air Force Research Laboratory (AFRL) and one developed by the European Space Agency (ESA). The ESA Spacecraft Onboard Interface Services (SOIS) protocol aims to work within the framework of the SpaceWire standard, blending PnP structures into existing SpaceWire features and retaining protocol-level support for legacy devices. The AFRL space plug-and-play architecture (SPA) protocol is geared more towards agility and adaptability to provide generalized support for more kinds of devices and networks (including blended networks of SpaceWire and other protocols). This effort investigated whether a common interface could be developed using a PnP adaptation layer to interact through both variants of plug and play, and a simulated SpaceWire Network Attached Storage (NAS) device was used as a challenge task. The project was extended to examine feasibility of performing OPNET Modeler simulation that integrated a SPA implementation.
Approach — The approach was to build a lightweight implementation of various components of the system combined with existing hardware and software so that experiments could be conducted. Using experience from the first half of the project, additional work was performed to better understand an actual SPA implementation to perform experiments in a combined simulation of the SPA with OPNET. A test bed was assembled using available SwRI resources. The test bed consisted of a SpaceWire network with two routers and Linux computers. An adaptation layer for the PnP capability was defined and implemented. A SPA middleware implementation developed by Utah State University was acquired from AFRL and ported to the physical system. Simulated producer, consumer, and NAS applications were written. The USU SPA was successfully operated using the test bed in both a raw mode and with the adaptation layer in place for the simulated applications. No ESA reference implementation was available; thus, a second SPA implementation was acquired from Broad Reach Engineering (with AFRL support). This implementation proved to be too different in its hardware and software interfaces to be practical to port to the test bed. The implementation was analyzed and it was determined, in principle, that it should be usable with the adaptation layer. The project was extended to investigate the feasibility of combining an OPNET simulation with an actual SPA implementation. The USU SPA V9.1 was used and it was verified that a simulation was feasible using OPNET co-simulation and a custom controller program external to OPNET. The external program provided an interconnect between the SPA executables and the OPNET internal model.
Accomplishments — This work showed that an adaptation layer was feasible to add to existing PnP implementations. The addition of the adaptation layer to the USU SPA implementation was straightforward and effective. A lightweight NAS was built, along with producer and consumer applications, which were connected using the adaptation layer and the USU SPA. The adaptation layer impact on system performance was negligible. A second SPA implementation was analyzed. This implementation was not directly operable on the underlying hardware. This version, however, would have been compatible with the adaptation layer. Also, although no reference implementation of the ESA approach existed, the adaptation layer concept was workable for that environment as well. Finally, in the project extension, it was shown that the SPA could be successfully integrated with the OPNET Modeler. The ability to perform software-in-the-loop (SIL) simulation (for example, the SPA) is an enabling factor in performing very high fidelity simulations of SpW networks.