A Generic SpaceWire Transport Layer

The transport layer is the essential part in the open system interconnection (OSI) reference model, since it is the interface between the software-oriented layers 5-7 and hardware-oriented layers 1-3. On the one hand, it provides a general approach for data exchange with the software-oriented layers, independent of the underlying hardware. On the other hand, it is responsible for an efficient and reliable use of the underlying hardware. These characteristics make the transport layer crucial for the effective usage of a communication system, as it significantly reduces the implementation effort for the software-oriented layers. The lack of a transport layer is a huge disadvantage. Combining the functionality of different communication layers into single application specific protocols can lead to the coexistence of multiple, non compatible approaches, resulting in a higher implementation effort for integrating new applications. Therefore, the existence of a transport layer is fundamental for both communication software and hardware, to provide established communication concepts, which are a precondition for the use of standardized software libraries, and to integrate modern computing trends (e.g. Big Data, Data-Mining, machine learning, cyber security). SpaceWire does not yet define a general transport layer. This paper presents the approach of a minimalist SpaceWire transport layer, as common base for the implementation of higher level protocols. It comprises both the hardware related SpaceWire transport node and the associated software counterpart as well as the associated protocol. The transport layer implementation is one result of our longstanding SpaceWire development and is already in use in several robotic systems.