A scientific study of the problems
of digital engineering for space flight systems,
with a view to their practical solution.
Spacewire: The Standard
Dr SM Parkes,
Applied Computing, University of Dundee,
Dundee, DD1 4HN, Scotland, UK
Tel: +44 1382 345194, Fax +44 1382 345509
email: sparkes@computing.dundee.ac.uk
Abstract
SpaceWire is an emerging standard for high-speed data handling which is intended to meet the needs of future, high-capability, remote sensing instruments. SpaceWire is based on two existing commercial standards, IEEE-1355 [1] and LVDS [2, 3] which have been combined and adapted for use on-board spacecraft. This paper provides a detailed description of the proposed SpaceWire standard. Applications and available integrated circuits and boards are described in another paper [4].
The paper begins with an overview of the requirements for high-speed data links on-board a spacecraft. The SpaceWire standard is then described in some detail. Issues that need to be resolved before the draft standard can be issued to the space industry for comment are highlighted. Finally the current and future work on the standard are summarized.
It should be noted that the information given in this paper is preliminary and likely to change. The intention here is to give visibility of the current state of the standard to European Space Industry and to encourage comment and criticism of the proposed standard.
SpaceWire is the result of the efforts of many individuals within the European Space Agency, European Space Industry and Academia. The ESA Digital Interface Circuit Evaluation (DICE) study, led by the University of Dundee, has tested LVDS with IEEE-1355 and is now drafting the SpaceWire standard document.
Table of Contents
I. Aims and Applications
II. Data Link Requirements
III. The Spacewire Standard
A. Overview
B. Physical Level
1. Cables
2. Connectors
3. EMC Specifications
C. Signal Level
1. Signal Level and Noise Margins
2. Data Encoding
D. Character Level
E. Exchange Level
F. Packet Level
G. Higher Level Protocols
IV. Conclusions
V. Acknowledgements
VI. References
List of Figures
Figure 1. Proposed Cable Construction
Figure 2. LVDS Operation
Figure 3. LVDS Signalling Levels
Figure 4. Data-Strobe (DS) Encoding
Figure 5. Data and Control Characters
Figure 6. Parity Coverage
Figure 7. Link Restart
Figure 8. Packet Format
Conclusions
This paper has provided an overview of the proposed SpaceWire standard.
Several issues have to be resolved before SpaceWire can be presented as a draft ESA standard:
1. Provide specification for space qualifiable cable and connectors.
2. Consider high-level virtual channel protocols.
3. Resolve problems with IEEE-1355 startup/reconnect problems.These activities are planned as part of the DICE study phase 2. A draft standard will be issued to members of a SpaceWire working group later in 1999 [4].
SpaceWire is set to become an important standard for satellite on-board data handling. It combines appropriate features from two commercial standards with improvements necessary to ensure that it is suitable for many space missions.
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