1. The CCSDS Spacecraft Onboard Interface Services (SOIS) Standards An Introduction
Stuart Fowell
6th October 2009

2. Overview SOIS Standardisation, OSI and SOA SOIS Architecture
SOIS Services
SOIS Prototyping and Reference Implementation
SOIS Introduction

3. CCSDS SOIS Standardisation
The Consultative Committee for Space Data Standards (CCSDS) developing recommendations for communication services onboard a spacecraft, handled by the Spacecraft Onboard Interface Services (SOIS) area
SOIS aims to provide a consistent interface to various low-level access methods, enabling a common interface to the application software
This is achieved through the providing a uniform set of services over any subnetwork
Eventual goal is reusable software that can be easily ported to new missions and run on a range of onboard buses without substantial modification
Beyond the uniform set of services over any subnetwork, this goal is to standarise interfaces to devices
Late configuration changes, e.g. relocation of thermistor, can be accommodated through simple spacecraft database changes without affecting onboard software
Consistent interface should provide an enabler for more complex, higher-level software architectures, e.g. fault-tolerant, distributed, software frameworks and autonomous, onboard mission planners
SOIS Introduction

4. SOIS, OSI and SOA
SOIS defined with reference to OSI, similar to aspects of SOA
SOIS defined as a layered architecture and services provided by each layer
Each service defined in terms of:
Service interface offered to higher layers
Protocol engine (procedures and PDUs)
May include time-outs on receiving PDUs
Required services from lower layers
Management Information Base (MIB)
All defined using structured English
Abstract definition, with no reference to implementation in hardware or software, programming languages, APIs etc.
SOIS Introduction

5. SOIS Architecture Organised into layers:
Subnetwork Layer provides access to the Data Link medium and provides a set of SOIS-defined services over the subnetwork defined by that medium
Transfer Layer optionally provides Transport- and Network-layer services based on existing protocols
Application Support Layer provides a number of capabilities commonly required onboard a spacecraft
Application Layer consists of mission-dependent applications that make use of the SOIS-defined services
All managed by Communication Management
SOIS Introduction

6. Typical subnetwork Subnetwork = Data Link Protocol Data Link Protocol
Physical I/F
Physical I/F
Datalink = Basic communication protocol
Physical = Connector, Pinout, electrical
Data Link Protocol
Data Link Protocol
RS422
RS422
ECSS Milbus Ext protocol
ECSS Milbus Ext protocol
Milbus
Milbus
ECSS SpaceWire Datalink
ECSS SpaceWire Datalink
ECSS SpaceWire Physical
ECSS SpaceWire Physical

7. SOIS Services SOIS Subnetwork Layer
Device Commanding, Data Acquisition & Virtualisation
File and Packet Store Access
Onboard Time Access
Message Transfer
Device Plug-and-Play
SOIS Introduction

8. SOIS Subnetwork Layer
Standardise basic communication services to be provided by a subnetwork
Services are mapped onto protocols and services provided by different data medium e.g. SpaceWire, MIL-STD-1553B and CAN
Not all services need to be provided by a subnetwork type
Provision against system requirement should be used to drive subnetwork selection
Packet Service – providing packet delivery over a single subnetwork
Memory Access Service – providing direct access (memory location read/write, includes block move and read/modify/write) to device memory
Synchronisation Service – providing spacecraft time and event synchronisation
Test Service – providing establishment of subnetwork functionality and availability
SOIS Introduction

9. SOIS Subnetwork Layer Mappings
MIL-STD-1553B
ECSS-E-ST-50-13C, “Interface and communication protocol for MIL-STD-1553B data bus onboard spacecraft”, 15 November 2008
Influenced by early drafts of SOIS services
Prototype mapping for BCs done by Astrium, RUAG
Recommended mapping for BCs and RTs to be produced in SOIS prototype
SpaceWire
ECSS-E-ST-50-12C, “SpaceWire - Links, nodes, routers and networks”, 31 July 2008
ECSS-E-ST-50-51C, “SpaceWire protocol identification”, 5 February 2010
ECSS-E-ST-50-52C, “SpaceWire - Remote memory access protocol”, 5 February 2010
ECSS-E-ST-50-53C, “SpaceWire - CCSDS packet transfer protocol”, 5 February 2010
QoS being addressed in variety of R&D projects, e.g. SpaceWire-RT/T/D protocols from SpaceNet project (University of Dundee)
Prototype mappings done by SciSys, UoD
Recommended mapping to be produced in SOIS prototype
CAN
ECSS working group in progress
Mapping to SOIS included in WG charter
Draft expected end 3Q 2010
SOIS Introduction

10. Device Commanding, Data Acquisition & Virtualisation
Typically used to access spacecraft hardware devices such as sensors and actuators
Allows reconfiguration of subsystems (e.g. change location, port etc) or replacement of devices (Star Tracker type A -> B) without affecting users
Device Access Service – device-dependant driver providing basic reading from and writing to devices regardless of location
Encapsulates access methods (protocol and addressing) to devices
Mapped onto subnetworks’ Memory Access and/or Packet Services
May be driven by Electronic Data Sheets (dynamic or build-time auto-code generation)
Device Data Pooling Service – maintaining an image of the states of a number of devices
Periodic data acquisitions from devices
Device Virtualisation Service – standard device driver providing reference to a device using a virtual, i.e., generic, image of a physical device
Standardise device interfaces into classes and associated functions
Map class interfaces to actual interfaces – “virtualisation”
SOIS Introduction

11. Device Commanding, Data Acquisition & Virtualisation
SOIS Introduction

12. File and Packet Store Access
Provides access to the spacecraft storage system
Encapsulates access methods (protocol and addressing) to storage systems (e.g. mass memories)
Can be provided at 2 levels:
Network file access protocol, e.g. NFS, mapped onto subnetwork’s Packet Service
Remote block storage protocol, e.g. ATA, mapped onto subnetwork’s Memory Access Service, e.g. RMAP, or subnetwork’s Packet Service
File Access Service – allows access to files and portions of their contents in local or remote file stores
File Management Service – allows management of files and directories in local or remote file stores
Packet Store Access Services – allows storage, retrieval and deletion of packets in a local or remote packet store
Packet Store Management Services – allows management of packet stores in local or remote packet store systems
SOIS Introduction

13. File Services
SOIS Introduction

14. Onboard Time Access Providing access to a local time source
Local time source may be synchronised with a master time source using a subnetwork’s Synchronisation Service
Time Access Service – providing access to, one-shot alarms and metronomes based on local time source
SOIS Introduction

15. Message Transfer
Discrete message transfer between applications/higher-level services
Isolates users from location
For inter-processor comms, maps onto subnetwork’s Packet Service
For intra-processor comms can use RTOS message queues
Four messaging models:
Send/receive
Query/response
Publish/subscribe
Announce (similar to multi-cast)
Can be used as basis for middlewares/software bus or for inter-partition communication
Message Transfer Service – providing application-to-application message exchange
SOIS Introduction

16. Device Plug-and-Play Plug-and-play of devices
Device (and network) discovery
E.g. discovery of powered up 1553 RTs or SpaceWire links, routers etc.
Management of subnetwork
E.g. allocation of addressing, configuration of routing
Service discovery
E.g. by reading Electronic Data Sheets (xTEDS) from device
User notification of discovered devices
Subnetwork Device Discovery Service – providing dynamic device recognition
Device Enumeration Service – providing support for dynamic spacecraft configuration
SOIS Introduction

17. SOIS Recommendations
Latest draft documents can be found in the SOIS working group’s collaborative working environment (CWE)
CCSDS SOIS Informational Report, CCSDS G-1, June 2007
2nd issue being published in 2010
Published as standard:
SOIS Subnetwork Packet Service, CCSDS M-1, December 2009
SOIS Subnetwork Memory Access Service, CCSDS M-1, December 2009
SOIS Subnetwork Synchronisation Service, CCSDS M-1, December 2009
SOIS Subnetwork Device Discovery Service, CCSDS M-1, December 2009
SOIS Subnetwork Test Service, CCSDS M-1, December 2009
Under Publication
SOIS Device Access Service, CCSDS R-2.1, March 2010
SOIS Device Data Pooling Service, CCSDS R-2.1, March 2010
SOIS Time Access Service, CCSDS R-2.1, March 2010
About to undergo 2nd and final agency review:
SOIS File and Packet Store Services, CCSDS R-1.5, March 2010
About to undergo 1st agency review:
SOIS Message Transfer Service, CCSDS R-0.4, March 2010
Under developmment:
SOIS Device Virtualisation Service, CCSDS R-0.2, January 2009
SOIS Device Enumeration Service, CCSDS R-0.1, January 2009
SOIS Introduction

18. SOIS Reference Implementation
SOIS Reference Implementation Study
ESA TRP
Jan 2008 – Feb 2009
SciSys prime, EADS Astrium sub-contractor
Objectives
Prototype the SOIS Software Suite within ESA’s RASTA facility
Provide feedback on the outcome of the prototyping in order to refine and complete the CCSDS SOIS recommendations
SOIS Introduction

19. RASTA Test Facility
Reference Avionics System Test-bench Activity (RASTA)
RASTA OBC supplied by Aeroflex Gaisler
LEON2 ASIC (100 ESA or LEON3 FPGA (40 SciSys
3 x SpaceWire links
2 x MIL-STD-1553B BC, RT or BM
+ others (CAN, Ethernet, UART and Direct I/O)
RTEMS drivers
STARDundee USB-SpaceWire Router & Linux PCs
PCI MIL-STD-1553B cards & Linux PCs
SOIS Introduction

20. SOIS Software Suite Acceptance Testing – Reference Mission
Low Cost, Single Instrument, Earth Observation Mission
SOIS Introduction

21. SOIS Proof of Concept SOIS Proof of Concept Study Objectives: ESA TRP
December 2009 – January 2011
SciSys prime, EADS Astrium sub-contractor, Gaisler equipment supplier
Objectives:
Standardise SOIS APIs
Implement all SOIS services, running over SpaceWire and MIL-STD-1553B
Inc. mapping onto ECSS-E-ST-50-13C for MIL-STD-1553B (BC and RT)
Optimise and characterise implementation of SOIS services on RASTA
Integrate SOIS services with other Avionics Components
TM/TC Module and Ground Unit, PUS, CFDP
SpaceWire-based Advanced Mass Memory & File Store
Legacy MIL-STD-1553B Remote Terminal Units
Prototype use of Electronic Data Sheets for SOIS Plug-and-Play
Develop SOIS Demonstrator
Provide Feedback to CCSDS
SOIS Introduction