"Network Discovery over SpaceWire"

Glenn P. Rakow
NASA Goddard Space Flight Center

Abstract

The trend for Satellite developments is for quicker development times and reuse of standard components.  For the military, the desire is to have developments that are days or weeks not months or years.  For these systems integrating standard “off the shelf” components that are “plug-and-play” will be a necessity.  Unfortunately, “off the shelf” does not mean Commercial “Off The Shelf” (COTS), because environmental requirements (radiation, voltage, temperature, etc.) are still important.  Since SpaceWire has become a de facto standard for satellite high-speed (>200Mbp) on-board communications, it will become important for SpaceWire to adapt to this “plug and play” environment.  Several things must happen for this to occur.  The first is to figure out what the network looks like, i.e., how pieces of the network, routers and nodes, are connected together; network discovery.  The second is for the components connected to the network to be understood so that they can communicate in a deterministic way.  The first element, network discovery, has already been achieved for a SpaceWire device.  This paper will discuss how the NASA SpaceWire Intellectural Property (IP) does Network Discovery.  SpaceWire is network topology independent and this imposes some challenges to perform network discovery.  The NASA algorithm assumes that all routers in the system have a “Router Identifier (ID)” that uniquely specifies it.  End Nodes that attach to the router do not require this ID but are identified in the device enumeration phase, after the network is discovered or drawn.  The commands that gather the information of the SpaceWire network are the Configuration 0 read commands.  The commands used to read the status of routers (configuration 0 space) must also allow a network manager to talk to routers for whom it does not know their Router IDs, but still obtain the specific Router ID information.  It must also know the Routers port number from where the responses are sent.  By using Path addressing, and the special configuration 0 space read commands the network connections may be drawn.  From this information the network manager may than configure the network and then perform device enumeration.

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