SpaceWire-D prototype and demonstration system: Networks & protocols, long paper

SpaceWire-D is an extension to the SpaceWire protocol that provides deterministic capabilities over existing SpaceWire equipment. The network is divided into segments using a virtual bus abstraction, where a virtual bus consists of a single RMAP initiator, one or more RMAP targets and the SpaceWire links that make up the paths between the initiator and the targets. Time-codes are broadcast periodically to provide time-division multiplexing, and a network schedule is defined by the allocation of virtual buses to time-slots. If a virtual bus has been allocated a time-slot, it is allowed to execute transactions to any of the targets within the virtual bus as long as the transactions complete their execution before the end of the time-slot. If the schedule is designed so that no virtual buses sharing a link are allocated the same time-slot, packets are no longer affected by blocking which allows the transaction execution times to be calculated and real-time constraints to be satisfied. The SpaceWire-D demonstration system has been designed to facilitate the verification of the draft standard. It consists of two RMAP initiators, twelve RMAP targets, a network manager device, a host PC and a routed SpaceWire network to connect the devices together. The LEON2-FT based initiator boards each contain an embedded SpaceWire-D software layer and an automated test scripting system, built on top of the RTEMS real-time operating system. The target boards respond to RMAP commands and provide event notification functionality on the backplane to allow for network activity monitoring. The network manager receives statistics and error information at the end of each schedule epoch, reported by the initiators, and informs the host PC so that it can be read, parsed and displayed to the user. Finally, the host PC runs a suite of software programs to configure, control and monitor the other devices in the demonstration system. This paper provides an overview of the SpaceWire-D protocol and describes the design and features of the SpaceWire-D demonstration system.