How to design, test and verify the physical layer of SpW networks: SpaceWire test and verification session, long paper

The AIT/AIV spacecraft test campaign undergoes an electrical verification program for all the units and instruments. The SpaceWire standard calls for LVDS signals in the physical layer and these are considered critical because the present LVDS technology is capable to drive signals up to 400 Mbit/s with low common mode voltage. Reliable SpaceWire communication can be difficult in the presence of induced noise, ground level differences, impedance mismatches, failure to effectively bias for idle line conditions, and other hazards associated with installation of a SpW network within the spacecraft. Therefore, the verification steps of SpW signals are very important and they shall be addressed with special care. Moreover, the new revision of the SpaceWire standard ECSS-E-ST-50-12C∗ rev.1 (currently under review) defines new requirements for the SpW signals in particular for the skew and the jitter budget and the margins. In addition, responsibilities for the two main actors (i.e. the unit manufacturer and the cable assembly manufacturer) are defined via jitter and skew budget calculation. All these aspects motivated ESA to the internal development of boards to perform the new requirement tests. This paper will summarize the related test campaign and the test coverage of various clauses of the new revision of the standard. A comprehensive plan and recommendations for the validation measurement of SpW link from the design to the final qualification/acceptance is proposed, distinguishing responsibilities among system architect, component manufacturer, unit supplier, cable assembly manufacturer and system integrator. References to on-going ESA projects will be presented. The effect on the overall skew and jitter budget calculation is discussed as well.