ECSS-E-ST-50-12C vs ECSS-E-ST-50-12C Rev.1, what’s the difference?

The SpaceWire Rev.1 revision aims to improve the SpaceWire standard without making substantial technical changes as noted in ECSS-E-ST-50-12C Rev.1 Annex A on page 122.

The Rev.1 document has an updated separation of layers with clearly defined interfaces including network, data link, encoding and physical whereas the July 2008 standard layers are defined as network, packet, exchange, character, signal and physical layer. Figure A-1 on page 122 lists the mapping of layers between the Rev.1 standard and the previous version, as shown below.

ECSS-E-ST-50-12C vs ECSS-E-ST-50-12C Rev.1 - Comparison of SpaceWire Layers

The revised standard also includes changes to the cable assembly, initialisation state machine, and broadcast codes. The changes are summarised below.

Changes to the cable assembly, state machine and broadcast codes sections are summarised below.

Cable Assembly

Cable assembly Type A and Type B are defined in clause 5.3.4. ECSS-E-ST-50-12C cable assemblies are identified as Type AL.

State Machine

The initialisation state machine is modified with new Sent NULL and Sent FCT signals, clarifying when the interface can move to state Run. LinkDisable asserted behaviour changes allow the state machine to remain in ErrorReset with Receiver Disabled.

Broadcast Codes

The Rev.1 SpaceWire standard defines broadcast codes as Distributed Interrupts and Time-codes in chapters 5.6.4 and 5.6.5.

  • Distributed interrupts support global interrupt traversal through a SpaceWire network supporting both interrupt request and interrupt acknowledgement.
  • Time-codes broadcast a regular incrementing tick signal through a SpaceWire network, supporting time distribution.