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SpaceWire

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SpaceWire Specifications
Created byEuropean Space Agency
Speed2.0–400 Mbit/s
StyleSerial
Hotplugging interfaceYes
External interfaceYes
Websitespacewire.esa.int/WG/SpaceWire/
SpaceWire Connector Specifications
Type Data connector
Production history
Designer European Space Agency
General specifications
Hot pluggable Yes
External Yes
Audio signal No
Video signal No
Pins 9
Connector Micro-D
Data
Data signal Yes
Bitrate 2.0–400 Mbit/s
Protocol Serial
Pinout
Pin Name Description
Pin 1 DIN+ Data In Pos.
Pin 2 SIN+ Strobe In Pos.
Pin 3 Inner Shield Ground
Pin 4 SOUT- Strobe Out Neg.
Pin 5 DOUT- Data Out Neg.
Pin 6 DIN- Data In Neg.
Pin 7 SIN- Strobe In Neg.
Pin 8 SOUT+ Strobe Out Pos.
Pin 9 DOUT+ Data Out Pos.

SpaceWireis aspacecraftcommunication networkbased in part on theIEEE 1355standard of communications. It is coordinated by theEuropean Space Agency(ESA) in collaboration with international space agencies includingNASA,JAXA,andRKA.

Within a SpaceWire network the nodes are connected through low-cost, low-latency,full-duplex,point-to-pointserial links, andpacket switchingwormhole routingrouters.

Architecture

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Physical layer

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SpaceWire's modulation and data formats generally follow thedata strobe encoding-differential ended signaling(DS-DE) part of the IEEE Std 1355-1995. SpaceWire utilizesasynchronous communicationand allows speeds between 2 Mbit/s and 200 Mbit/s, with initial signalling rate of 10 Mbit/s.[1]DS-DE is well-favored because it describes modulation, bit formats, routing,flow control,anderror detectionin hardware, with little need for software. SpaceWire also has very low error rates, deterministic system behavior, and relatively simple digital electronics. SpaceWire replaced oldPECLdifferential drivers in the physical layer of IEEE 1355 DS-DE bylow-voltage differential signaling(LVDS). SpaceWire also proposes the use of space-qualified 9-pin connectors.

SpaceWire and IEEE 1355 DS-DE allows for a wider set of speeds for data transmission, and some new features for automaticfailover.The fail-over features let data find alternate routes, so a spacecraft can have multiple data buses, and be madefault-tolerant.SpaceWire also allows the propagation of time interrupts over SpaceWire links, eliminating the need for separate time discretes.

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Each transferred character starts with a parity bit and a data-control flag bit. If data-control flag is a 0-bit, an 8-bit LSB character follows. Otherwise one of the control codes, including end of packet (EOP).[2]

Network layer

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The network data frames look as follows:

Address byte Address byte... Protocol ID Frame data

One or more address bytes are used for the routing. Addresses are either physical ones (0–31), or logical ones. The difference is that the physical addresses are deleted from the frame header during routing - which is used for hop-based routing (based on path specified in the frame itself). Logical addresses may be deleted as well, depending on the router configuration.

Interconnection

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The hardware devices may be connected either directly, or via a SpaceWire router. In the former case, usually pairs of devices are used to guarantee a fail-safe operation, which is handled by the software.

A SpaceWire router is usually acrossbar switch-type device, operating inwormhole switchingmode. This also may limit the speed of the communication to the lowest common speed.[3]The routing decisions are based on the programmed routing table and the initial incoming frame contents.

Uses

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SpaceWire is used all around the globe.[4] Its use began primarily inESAprojects, but it is currently used byNASA,JAXA,RKA,and many other organizations and companies. Some NASA projects using it include theJames Webb Space Telescope,Swift'sBurst Alert Telescope,theLunar Reconnaissance Orbiter,LCROSS,theGeostationary Operational Environmental Satellite(GOES-R), and the SCaN Testbed, previously known as the Communications, Navigation, and Networking Reconfigurable Testbed (CoNNeCT). It has also been selected by theUnited States Department of Defensefor Operationally Responsive Space. SpaceWire initiatives are being coordinated between several space agencies in the frame ofConsultative Committee for Space Data Systems(CCSDS) in order to extend its communication model to the network and transport layers of theOSI model.

SpaceWire supports highlyfault-tolerantnetworks and systems, which is one reason for its popularity.[5]

Protocols

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The ESA has a draft specification in place for the Protocol ID.

The following Protocol ID's have been assigned in ECSS-E-ST-50-11:

Protocol ID Name Description
1 Remote Memory Access Protocol(RMAP) used to remotely access/alter register configuration of the devices
2 CCSDS Packet Transfer Protocol[6] a common protocol used for sending Telecommands and receiving Telemetry
238 Proposal forReliable Data Delivery Protocol(RDDP) used onGOES-R
239 Serial Transfer Universal Protocol(STUP) Used on SMCS-332ASIC

References

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  1. ^"SpaceWire's User Guide"(PDF).Star-dundee.Retrieved27 October2019.chapter 3.3.5
  2. ^"SpaceWire Characters".Star-dundee.Retrieved28 October2018.
  3. ^"Radiation-Tolerant 10x SpaceWire Router"(PDF).Gaisler.Retrieved28 October2018.
  4. ^"Who Uses SpaceWire? - STAR-Dundee".Star-dundee.Retrieved28 October2018.
  5. ^Dr Barry M Cook; Paul Walker. "Ethernet over SpaceWire - software issues".4links.co.uk, p. 2[dead link]
  6. ^"Space Packet Transfer Protocol"(PDF).Public.ccsds.org.Retrieved28 October2018.

Other sources

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SpaceWire IP Cores:

Articles:

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