Time-triggered data transfers over SpaceWire for distributed systems

SpaceWire as a communication technology for serial data transfer is widely used in the space domain. Although the related ECSS standard describes how data routing in SpaceWire networks shall be implemented, the possibilities of applying real-time traffic are quite limited. As soon as more complex networks with cascades of routers are required, the proposed prioritization given by the ECSS standard is not suitable. This paper introduces a way to remove this limitation. We will present a system capable if establishing a time-triggered data transfer over SpaceWire. This is done by exploiting distributed interrupts which are part of the currently revised ECSS-E-ST-50-12C standard. These interrupts will serve as a pulse which is used to mark a specific point in time and a related schedule position as valid inside the whole network. This is a different approach than using SpaceWire time codes directly. Our approach allows us to establish a decentralized time distribution instead of relying on a single time providing unit used in existing SpaceWire enhancements. Additionally it removes the limitation of being limited to schedule lengths of 64 slots.