Mixed SpaceWire - SpaceFibre Networks by 5kI048i8

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									  Mixed SpaceWire - SpaceFibre Networks


                      Martin Suess(1, Steve Parkes(2
                        (1European Space Agency,
                           (2University of Dundee

                      E-mail: martin.suess at esa.int,
                    sparkes at computing.dundee.ac.uk


2-4 November 2008        2nd International SpaceWire Conference
                                       in Nara, Japan             Slide : 1
                      MIXED SPACEWIRE - SPACEFIBRE NETWORKS




Overview

•    Introduction
•    SpaceWire – SpaceFibre comparison
•    SpaceFibre Virtual Channels
•    Priorities and Group Adaptive Routing
•    Mixed Network Examples
•    SpaceFibre Outlook
•    Conclusion




2-4 November 2008      2nd International SpaceWire            Slide : 2
                        Conference in Nara, Japan
                         MIXED SPACEWIRE - SPACEFIBRE NETWORKS




Introduction

• SpaceWire supports bi-directional traffic of up to 200Mbit/sec
  over a distance up to 10m.
• SpaceFibre shall be capable to improve to both figures by at
  least a factor of 10:
   – Data rates ≥ 2.5Gbit/sec
   – Distance ≥ 100m
   – Provide additional features like galvanic isolation
• This requires a number of modifications at different levels of the
  protocol stack.
• The aim is to maintain compatibility between SpaceWire and
  SpaceFibre on Packet and Network level.
• In the following the solutions implemented in the SpaceFibre
  breadboard are presented



2-4 November 2008        2nd International SpaceWire             Slide : 3
                          Conference in Nara, Japan
                       MIXED SPACEWIRE - SPACEFIBRE NETWORKS




Physical & Signal Level - Optical

• SpaceWire uses cables with 4 twisted pairs with nine-pin micro
  miniature D-type connectors.
• SpaceFibre uses two optical fibres as medium:
   – The Draka MaxCap 300 radhard graded-index multimode
     fibre has been selected after testing
   – A cable protecting the fibre was designed based on
     expanded polytetrafluoethylene
   – Diamond AVIM connectors where already qualified for space
• Electro optical transceivers produce 850-nm laser light with a
  power of 3dBm peak




2-4 November 2008       2nd International SpaceWire            Slide : 4
                         Conference in Nara, Japan
                             MIXED SPACEWIRE - SPACEFIBRE NETWORKS




      Diamond AVIM connectors and electro optical transceiver breadboard


2-4 November 2008            2nd International SpaceWire             Slide : 5
                              Conference in Nara, Japan
                                MIXED SPACEWIRE - SPACEFIBRE NETWORKS




Physical & Signal Level - Electrical

• In addition an electrical version for short distances forseen.
• Prototype used 4 coaxial cables with SMA connectors.
• The electrical interface of the transceivers use Current Mode
  Logic (CML).
• CML is directly used as signal level in the electrical version.
• Tolerance to common mode voltage differences can be
  improved by blocking capacitors.
• More investigations are needed before physical & signal level
  definition of electrical SpaceFibre.




                    AC coupling of a CML transmitter and receiver

2-4 November 2008               2nd International SpaceWire             Slide : 6
                                 Conference in Nara, Japan
                      MIXED SPACEWIRE - SPACEFIBRE NETWORKS




Character Level - 8B10B Encoding

• SpaceWire defines data and 4 control characters
   – FCT, EOP, EEP, ESC
   – The combination of ESC with FCT and Data Characters
     defines the Null control code and the Time-Codes
• SpaceFibre characters are based on 8B10B encoding
   – DC balanced data signal plus 12 special characters for
     control functions
   – Three of these special characters are comma characters
   – Comma characters contain a unique sequence of ones and
     zeroes that are used for character alignment




2-4 November 2008     2nd International SpaceWire             Slide : 7
                       Conference in Nara, Japan
                        MIXED SPACEWIRE - SPACEFIBRE NETWORKS




Character Level - Ordered Sets

• Ordered Sets are a sequence of 4 characters starting with a
  comma character (K28.5)
• The second character defines the type of ordered set
• The last two characters can carry additional information
• Ordered Sets greatly extend the possibility to embed control
  information in the data steam
• Several types of ordered sets are defined for SpaceFibre:
   – Link-level, power management, reset, flow control, faming
      and user ordered sets
   – User ordered sets are used to propagate time codes and
      interrupts though the network




2-4 November 2008       2nd International SpaceWire             Slide : 8
                         Conference in Nara, Japan
                        MIXED SPACEWIRE - SPACEFIBRE NETWORKS




Exchange Level - Flow Control & Framing

• SpaceWire uses flow control to prevent receive buffer over flow.
    – Each FCT indicates 8 Bytes of free buffer space.
• SpaceFibre maintains the concept of flow control.
    – Granularity of flow control is increased due to higher
      bandwidth.
    – Each FCT ordered set controls the flow of one frame of
      maximum 255 data words.
• A frame starts with a Start of Frame ordered set and ends with
  an End of Frame ordered set.
• The End of Frame ordered set contains the 16 bit CRC of the
  frame for error detection.
• SpaceWire packets are segmented into frames and
  reassembled at link level.



2-4 November 2008       2nd International SpaceWire             Slide : 9
                         Conference in Nara, Japan
                         MIXED SPACEWIRE - SPACEFIBRE NETWORKS




Virtual Channels in SpaceFibre

• Flow control and start of frame ordered sets contain the virtual
  channel number.
• With separate frame buffers the virtual channel data flow is
  logically separated while using the same medium.
• Congestion in one virtual channel does not influence the traffic
  in the other virtual channels.
• A SpaceWire packet in one virtual channel can pass a packet in
  another virtual channel.
• Priorities can be used to control the access of a virtual channel
  to the physical medium so that the higher priority channel has
  always direct access.




2-4 November 2008        2nd International SpaceWire             Slide : 10
                          Conference in Nara, Japan
                    MIXED SPACEWIRE - SPACEFIBRE NETWORKS




Virtual Channels in SpaceFibre


           VC1            Virtual Link 1                     VC1
          Buffer                                            Buffer


           VC2             Virtual Link 2                    VC2
          Buffer                                            Buffer
                               SpaceFibre
           VC3             Virtual Link 3                    VC3
          Buffer                                            Buffer


           VC4             Virtual Link 4                    VC4
          Buffer                                            Buffer




2-4 November 2008   2nd International SpaceWire                Slide : 11
                     Conference in Nara, Japan
                       MIXED SPACEWIRE - SPACEFIBRE NETWORKS




Number of Virtual Channels in a SpaceFibre Link

• Maximum number of virtual channels is 256.
• In practice less will be used to limit the number of buffers
  needed.
• The individual virtual channels must be accessible without
  blockage or bottle neck.
• In a SpaceWire router the total number of ports for path
  addressing is limited to 31.
• The SpaceWire standard allows to use two consecutive address
  bytes for path addressing in large routers.
   – The first path address byte indicates the SpaceFibre link.
   – The second path address byte indicates the virtual channel
      number.
• Beyond this some of the virtual channels could be accessed by
  logical addressing only.

2-4 November 2008      2nd International SpaceWire             Slide : 12
                        Conference in Nara, Japan
                                              MIXED SPACEWIRE - SPACEFIBRE NETWORKS




SpaceWire - SpaceFibre Router
                                                     SpaceFibre Port 1
                              Internal




                                              VC 1

                                                     VC 2

                                                            VC 3

                                                                   VC 4

                                                                          VC 5

                                                                                 VC 6
                            Configuration                                                            SpaceFibre
                               Port 0


                                                                                                                            Router example with:




                                              1,1
                                                     1,2
                                                            1,3
                                                                   1,4
                                                                          1,5
                                                                                 1,6
                                   0
                        Crossbar                                                                                            • 3 SpaceFibre links
                         Switch

 SpW
       SpaceWire
         Port 4    4                                                                                                          with 6 virtual
       SpaceWire
                                                                                                                              channels each
         Port 5    5
                                                                                                                            • 7 SpaceWire links
 SpW

       SpaceWire
                                                                                        2,1   VC 1
                   6
         Port 6
                                                                                                                            • 2 External ports




                                                                                                        SpaceFibre Port 2
 SpW                                                                                    2,2   VC 2

       SpaceWire                                                                        2,3   VC 3
         Port 7    7                                                                                                        SpaceFibre
 SpW
                                                                                        2,4   VC 4
       SpaceWire
                   8
 SpW     Port 8                                                                         2,5   VC 5
                                                                                                                            • Non blocking crossbar
       SpaceWire                                                                        2,6   VC 6
 SpW     Port 9    9                                                                                                          switch provides direct
       SpaceWire
                   10
                                                                                                                              access to every virtual
 SpW    Port 10
                                                                                                                              channel
                                              3,6
                                                     3,5
                                                            3,4
                                                                   3,3
                                                                          3,2
                                                                                 3,1
                          11



                                       12




                        External   External
                                              VC 6

                                                     VC 5

                                                            VC 4

                                                                   VC 3

                                                                          VC 2

                                                                                 VC 1




                        Port 11    Port 12
                                                                                                     SpaceFibre

                                                     SpaceFibre Port 3




2-4 November 2008                              2nd International SpaceWire                                                               Slide : 13
                                                Conference in Nara, Japan
                         MIXED SPACEWIRE - SPACEFIBRE NETWORKS




Virtual Channel Priorities & Group Adaptive Routing

• Each virtual channel can provide the full bandwidth of the
  SpaceFibre link.
• If two or more virtual channels request a bandwidth higher than
  the full bandwidth of the link some arbitration is required.
• Priorities can be assigned to virtual channels:
    – The virtual channel with higher priority is allowed to send the
       next frame.
    – Round robin arbitration is performed between virtual
       channels of the same priority.
• User ordered sets for time-code and interrupt distribution have
  priority and are sent in the middle of the frame currently
  transmitted.
• SpaceWire-RT protocol should be used to provide Quality of
  Service beyond priorities.

2-4 November 2008         2nd International SpaceWire            Slide : 14
                           Conference in Nara, Japan
                        MIXED SPACEWIRE - SPACEFIBRE NETWORKS




Group Adaptive Routing

• If packets are routed through the same virtual channel the
  access is arbitrated by the router.
• Routers can provide group adaptive routing among virtual
  channels with the same priority:
    – Two packets to the same logical address can use parallel
      virtual channels.
    – The receiving side can then decide which should be
      processed first.
    – Available overall bandwidth is not increased.
• Routers can provide group adaptive routing among several
  SpaceFibre links.
    – This can be used to increase the available bandwidth.




2-4 November 2008       2nd International SpaceWire             Slide : 15
                         Conference in Nara, Japan
                                      MIXED SPACEWIRE - SPACEFIBRE NETWORKS




  Network Example – Single SpaceFibre Link



High Data Rate                                    Mass Memory                 Modulator &
  Instrument         SpaceFibre                                               Downlink Unit
  Electronics


                     Sp           e
                        ce Fibr
                        a
                     Sp
                           e
                           F
                        a c i b re                Mass Memory
                                                   redundancy                 Modulator &
High Data Rate
                                                                              Downlink Unit
  Instrument
                                                                               redundant
  Electronics        SpaceFibre
  redundant




 2-4 November 2008                    2nd International SpaceWire                     Slide : 16
                                       Conference in Nara, Japan
                                                           MIXED SPACEWIRE - SPACEFIBRE NETWORKS




SpaceFibre as Backbone

                 Unit 2                                                      Unit 5                                                  Unit 8

   Unit 1                    Unit 3                            Unit 4                    Unit 6                        Unit 7                      Unit 9
                SpW




                                                                            SpW




                                                                                                                                    SpW
                SpW




                                  SpW




                                                                                              SpW




                                                                                                                                                        SpW
          SpW




                                                                      SpW




                                                                                                                              SpW
                            SpW




                                                                                        SpW




                                                                                                                              SpW




                                                                                                                                                  SpW
                      SpW




                                                                                  SpW




                                                                                                                                            SpW
           SpaceWire,                                                  SpaceWire,                                              SpaceWire,
    SpW




                                        SpW




                                                                SpW




                                                                                                    SpW




                                                                                                                        SpW




                                                                                                                                                              SpW
           SpaceFibre                         SpaceFibre               SpaceFibre                         SpaceFibre           SpaceFibre
          Routing Switch                                              Routing Switch                                          Routing Switch



           SpaceWire,                                                  SpaceWire,                                              SpaceWire,
           SpaceFibre                         SpaceFibre               SpaceFibre                         SpaceFibre           SpaceFibre
          Routing Switch                                              Routing Switch                                          Routing Switch




2-4 November 2008                                          2nd International SpaceWire                                                    Slide : 17
                                                            Conference in Nara, Japan
                                                             MIXED SPACEWIRE - SPACEFIBRE NETWORKS




Mixed Networks
                Inst 3                   SpW                                                                   Unit 2
                                        SpW
       Inst 2                    SpW
                                                                                                                                            Unit 3
                                SpW


   Inst 1                 SpW                                                                        Unit 1




                                                                                                                             SpW




                                                                                                                                                   SpW
                                                                                                                                             SpW
                         SpW




                                                                                                        SpW
                                                                                                              SpW
                                                SpaceWire,                                               SpaceWire,




                                                                                                  SpW
   High Data Rate                                                                                                                                                     Mass
                           SpaceFibre           SpaceFibre                         SpaceFibre            SpaceFibre                                  SpaceFibre
     Instrument                                                                                                                                                      Memory
                                               Routing Switch                                           Routing Switch
     Electronics
                                                 SpaceFib.




                                                                                                                                                                      Mass
   High Data Rate                                                                                                                                                    Memory




                                                                                                                               SpaceFibre
     Instrument                            SpaceWire,                                                 SpaceWire,                                   SpaceFibre      redundancy
     Electronics          SpaceFibre       SpaceFibre                           SpaceFibre            SpaceFibre
     redundand                            Routing Switch                                             Routing Switch


                                                                                                                                    Modulator &




                                                                                                                SpaceFibre
                                                                                                                                    Downlink Unit


                                                                                             Modulator &
                                                                                             Downlink Unit



2-4 November 2008                                            2nd International SpaceWire                                                                          Slide : 18
                                                              Conference in Nara, Japan
                    MIXED SPACEWIRE - SPACEFIBRE NETWORKS




SpaceFibre Breadboarding




2-4 November 2008   2nd International SpaceWire             Slide : 19
                     Conference in Nara, Japan
                    MIXED SPACEWIRE - SPACEFIBRE NETWORKS




SpaceFibre Breadboarding




2-4 November 2008   2nd International SpaceWire             Slide : 20
                     Conference in Nara, Japan
                         MIXED SPACEWIRE - SPACEFIBRE NETWORKS




SpaceFibre Outlook

• A first SpaceFibre prototype covering all levels has been
  implemented and tested.
• A first outline specification has been published and discussed in
  the frame of the SpaceFibre working group.
• The experience gained will be consolidated and used for the
  development of a SpaceFibre demonstrator.
• The SpaceFibre Demonstrator activity will target:
   – Development of a SpaceFibre IP core,
   – Test and validation of IP core using existing prototype,
   – SpaceFibre Demonstrator implementation based on Actel
      FPGA and Wizard Link SerDes,
   – Preparation of a SpaceFibre specification as input for the
      standardisation process.


2-4 November 2008        2nd International SpaceWire             Slide : 21
                          Conference in Nara, Japan
                       MIXED SPACEWIRE - SPACEFIBRE NETWORKS




Conclusion

• The different levels of SpaceFibre have been compared with
  SpaceWire.
• SpaceWire and SpaceFibre is intended to be fully compatible on
  Packet and Network level.
• This allows the easy implementation of mixed SpaceWire –
  SpaceFibre networks.
• Some examples of those networks have been presented.
• This compatibility is seen as essential feature of SpaceFibre.
• Experience has been gained with a prototype implementation.
• As next step a demonstrator will be developed based on space
  qualified components.
• Standardisation in ECSS is envisioned in corporation with the
  other space agencies.


2-4 November 2008       2nd International SpaceWire            Slide : 22
                         Conference in Nara, Japan

								
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