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NASA SpaceWire Architectures: Present & Future
Glenn Parker Rakow NASA – Goddard Space Flight Center 2006 MAPLD International Conference Washington, D.C. September 25, 2006
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Current SpaceWire Architectures: Swift Data Flow
Detectors & Instrument Readout Electronics Mem SpW Processor DSP Cmd Bus CDH ACS 16 Instrument CDH Spacecraft Back - plane 1553 SpaceWire point-to-point links 16 links from segmented detector array & readout Electronics to Instrument CDH Science Data & Commands PCI Instrument CDH to Memory Memory to DSP MIL-STD-1553 CMD bus to Spacecraft
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Current SpaceWire Architectures: LRO Data Flow
Routed SpaceWire traffic End-node routers on C&DH boards Used as Serial backplane Single Board Computer Board Instrument Interface Board S-Band Communication Board Ka-Band Communications Board Interface to moderate rate instruments Not memory mapped like RMAP or GAP Side band signaling using Time-Codes 1pps Barker code detect – uplink Upper level flow control on downlink frames MIL-STD-1553 Interface to spacecraft subsystem Used for low-rate heritage instruments Low - Rate Parallel Bus Instr Instr A A Instr Instr B B Xpndr Xpndr Instr Instr C C Hi Hi - - Rate Rate HGA HGA SpaceWire SpaceWire SpaceWire SpaceWire Router Xmtr Xmtr Low Rate/ Low Rate/ Unique Unique Low - Rate serial bus serial bus SpaceWire SpaceWire SpaceWire SpaceWire SpaceWire Router SpaceWire SpaceWire Router SpaceWire Router Router Router Router High High Power Power Low rate Low rate Processor Processor Memory Memory IO IO rate rate Supply Supply Comm Comm Comm Comm Parallel Bus Parallel Bus Parallel Bus Backplane Backplane C&DH C&DH
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Current SpaceWire Architectures: JWST Data Flow
FPE # 2 FPE # 3 FPE # 4 FPE # 5
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Current SpaceWire Architectures
JWST Routed SpaceWire traffic From 4 instruments to local router to end node router (Instrument C&DH [IC&DH]) (cable) ICDH end node router to hardware processors (same box over backplane) Hardware processors to compression engine (same box over backplane) Compression engine to recorder (cable) GOES-R – Point-to-point links Instrument - C&DH with Reliable Data Delivery Protocol
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Traditional Systems Legend:
Different physical interfaces using different protocols that require unique hardware and software to bridge between them Serial interface at one point per NIC Extra board area and more power for multiple interfaces Only boards in same enclosure have memory mapped access via arbitration Enclosures represent limited access Reuse & reconfigurability limited Purple Red Black Purple Blue Purple Red – High-speed interface Black – Discrete sync pulse Blue – TDMA low rate bus (MIL_STD-1553) Purple – Parallel Backplane Legend: Black
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Future Systems Legend: Blue Blue Blue Lt. Blue Red Red Blue Blue Blue
Non-Blocking Cross-Bar Switch Red Red Blue Blue Blue Same protocols supported across both physical interfaces SpaceWire and SpaceFibre Bridged by hardware router Low-level protocols (RMAP & GAP) for memory mapped DMA or single transactions – no software required & blurs enclosure boundaries Plug and Play network mapping and Change-of-Status indication supported in hardware Coming soon! Tunnel higher layer protocols Lt. Blue Blue Red Hardware bridge Between SpaceWire & SpaceFibre Legend: Red – SpaceFibre (optical or copper) Blue – SpaceWire Lt Blue – Local port interface (parallel)
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Advantages One communications infrastructure
Simplifies system design Consists of 2 different physical layers SpaceWire SpaceFibre Bridged in hardware via routing switch Seamless integration Supports low-level & high-level protocols Virtual serial backplanes RMAP & GAP Upper layer protocol may be identified Via Protocol ID (PID) Low latency bus Wormhole routing Side-Band signaling Reducing number of interfaces Time-Code enhancements Pending May be used as a time-triggered or event triggered bus Time-triggered via Time-code defined slots Command bus features have been addressed Cable redundancy (presented later) Transparent mechanism has been implemented Proposed for standardization Data retries Protocol ID (PID) can accommodate Retry protocols MIL-STD-1553 over SpaceWire (no PID assigned) Reliable Data Delivery Protocol (RDDP) (no PID assigned)
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System Engineer Toolkit
Router blockage prevention Time-out Max length Buffers match packet size Optimize throughput Full Duplex Cmd & Tlm opposite directions Dedicated link for low latency Priority routing SpaceFiber (cell based virtual channels) Long distance Isolation EMC/EMI Bridge to SpW via hardware router SpaceFiber High Rate Group Adaptive Routing Across multiple SpW links Redundant cables TLM CMD Multiple SpW local ports to prevent blocking; increase throughput Redundant paths Message sharing Time-critical network Consensus computing Time-codes Near zero-jitter across entire network Synchronization TDMA 1 pps Time-Code expansion Interrupts Polling Multi-TimeCode Group Adaptive Routing Multiple SpW links
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Conclusions Simple protocol that is being developed from bottom up to meet advanced spacecraft applications One bus standard can meet requirements Real time control Large data throughput Safety Guaranteed Low latency High reliability Reuse & reconfiguration of systems easier with standard interface Modular functions with standard interface Serial interface cable backplane Provide system engineers more “tools” for more efficient designs
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