1. SOIS and Software Reference Architecture
F. Torelli DASIA Malta 17/05/2011
ESA UNCLASSIFIED – For Official Use

2. Outline SOIS architecture and services
SOIS architecture and Avionics System Reference Architecture
Impacts to the design of flight software
Status of SOIS publications and related developments
Conclusions
ESA UNCLASSIFIED – For Official Use

3. SOIS architecture and services
ESA UNCLASSIFIED – For Official Use

4. CCSDS SOIS Architecture
SOIS provides an abstraction of the functionality of the spacecraft units in a layered fashion.
Standard Services
ECSS Standard Protocols
ESA UNCLASSIFIED – For Official Use

5. Sub-Network Services Sub-network services:
abstract from the physical location (within the spacecraft) of the unit to be accessed
abstract from the datalink protocol required by a specific communication media to access a unit
abstract from time constrains strictly related to the specific communication media used to access a unit
abstract from the addressing scheme required by a specific communication media to identify a unit.
ESA UNCLASSIFIED – For Official Use

6. Command & Data Acquisition Services
abstract from the protocol required to control the device (Device Access Service)
abstract from the type of communication service (i.e. memory access, packet-base) required to access the device (Device Access Service)
abstract from time constrains strictly related to the device specific access protocol (Device Access Service)
decouple device physical access from device data consumption by the applications (Device Data Pooling Service)
add ontology to the raw command and data information related to devices (Device Virtualisation Service)
provide a uniform interface for each class of devices, independent from their actual implementation (Device Virtualisation Service).
ESA UNCLASSIFIED – For Official Use

7. Other Application Support Services
Time Access Service:
abstracts from the mechanisms required to access the on-board reference time and to handle time alarms.
Message Transfer Service:
provides a high level and uniform mechanism to communicate between software applications within the spacecraft.
File and Packet Store Service:
provides a standardised interface to mass memory file and packet stores
abstracts from the implementation details related to the mass memory file systems.
ESA UNCLASSIFIED – For Official Use

8. Plug and Play Services Plug and Play Services:
provide mechanisms to discovery and configure devices connected to a sub-network
provide mechanisms to handle units redundancy
provide the means to interpret the content of Electronic Data Sheets and to configure the other services accordingly (C&DA).
ESA UNCLASSIFIED – For Official Use

9. Protocols supporting the Services
The services are complemented by protocols
implement the functionality specified by SOIS.
Sub-Network Protocols:
Mil-Std-1553, ECSS-E-ST-50-13C
CAN, ECSS-E-ST-50-15C draft
Spacewire, ECSS-E-ST (RMAP), ECSS-E-ST-50-XX (SpW-D)
Message Transfer Service Protocol:
Asynchronous Message Service, CCSDS B-0
File and Packet Store Service Protocols:
Network File Access, Network Packet Access and Remote Block Storage Protocols need to be standardised
TBD
AMS
ESA UNCLASSIFIED – For Official Use

10. SOIS and Avionics System Reference Architecture
ESA UNCLASSIFIED – For Official Use

11. Avionics System Reference Architecture
Onboard Communications H/W (e.g. MIL-STD-1553B, SpaceWire, CAN RS422)
OBC Hardware
CAN
MIL-1553
TM/TC
RS422
SpW
CPU/
NGmP
EEPROM
Boot PROM
OBTimer
SGM
HW watchdog
Software bus
Security Unit
Solid State Mass Memory File/ Compress/ Encrypt
Payloads & Instruments
SSMM
RTU/ Intelligent IO
Payload Computer
SOIS Layers
Legacy devices
Standardized devices
Intelligent devices
ADCs / DACs
Sensor and actuators
RAM
DSP
Digital Sensorbus
Space Linux
Application BB (mission dependent)
Plan/ Autonomy
Framework
System mode mgmt
Central FDIR
AOCS
P/L Manager
Thermal
Power
OBT Mgmt
Satellite Conf and Eqpt Mgmt
SSMM Mgmt
Execution platform
BSP
SOIS Subnetwork layer (1553, CAN, SpW)
(including HDSW)
Container services
Connector services
PUS specific
Component services
Abstract component services
PUS and MTL services
OBCP
interpreter
Avionics Equipment virtual devices =SOIS DVS
PUS monitoring
RTOS
Context
Mgmt
On-board time =SOIS TAS
Communication services addressing physical distribution across nodes
= SOIS MTS
Libraries: mathematical, etc.
ESA UNCLASSIFIED – For Official Use

12. SOIS in the Avionics System Reference Architecture 1/2
On-Board Computer (OBC):
The full set of SOIS services is intended for implementation in the OBC flight software as part of the Execution Platform building block.
Other Equipments:
A reduced subset of SOIS service is foreseen for the external units such as RTUs, Solid State Mass Memory, Intelligent Sensors and Actuators, Payloads in accordance with their functionality and supported features.
ESA UNCLASSIFIED – For Official Use

13. SOIS in the Avionics System Reference Architecture 2/2
Onboard Communications H/W (e.g. MIL-STD-1553B, SpaceWire, CAN RS422)
OBC Hardware
CAN
MIL-1553
TM/TC
RS422
SpW
CPU/
NGmP
EEPROM
Boot PROM
OBTimer
SGM
HW wdog
Software bus
Security Unit
Solid State Mass Memory File/ Compress/ Encrypt
Payloads & Instruments
SSMM
RTU/ Intelligent IO
Payload Computer
SOIS Layers
Legacy devices
Standardized devices
Intelligent devices
ADCs / DACs
Sensor and actuators
RAM
DSP
Digital Sensorbus
Space Linux
Application BB (mission dependent)
Plan/ Autonomy
Framework
System mode mgmt
Central FDIR
AOCS
P/L Manager
Thermal
Power
OBT Mgmt
Satellite Conf and Eqpt Mgmt
SSMM Mgmt
Execution platform
BSP
SOIS Subnetwork layer (1553, CAN, SpW)
(including HDSW)
Container services
Connector services
PUS specific
Component services
Abstract component services
PUS and MTL services
OBCP
interpreter
Avionics Equipment virtual devices =SOIS DVS
PUS monitoring
RTOS
Context
Mgmt
On-board time =SOIS TAS
Communication services addressing physical distribution across nodes
= SOIS MTS
Libraries: mathematical, etc.
ESA UNCLASSIFIED – For Official Use

14. Impacts to the design of flight software
ESA UNCLASSIFIED – For Official Use

15. Traditional Flight Software
In a traditional flight SW system, AOCS and equipment time requirements defining the bus schedule also drive the flight SW architecture and the SW tasks schedule.
The system is designed as a “monolithic” entity tailored for the specific mission.
Bus and ASW Time Domain Mixed
Payload 2 Manager
OBCP Interpreter
MTL Manager
MTL Manager
TC Manager
AOCS Processing
Payload 1 Manager
EEPROM Manager
Science TM Processing
Scrubbing
HK TM Processing
HK TM Processing
HK TM Processing
Mass Memory
Monitoring
Mode Manager
MilBus Manager
MilBus Manager
MilBus Manager
MilBus Manager
MilBus Manager
MilBus Manager
AOCS
Acquisitions
Payload 1
Acquisitions
Payload 2
Commanding
AOCS
Commanding
Large Data Transfer
Payload 2
Acquisitions
Minor Frame 0
(125 msec)
Minor Frame 1
(125 msec)
Minor Frame 2
(125 msec)
Minor Frame 3
(125 msec) …
Minor Frame 6
(125 msec)
Minor Frame 7
(125 msec) t
Major Frame (1 sec)
ESA UNCLASSIFIED – For Official Use

16. Motivations for an Improvement
Such a synchronous schedule works to accomplish relatively simple
mission requirements, however:
to improve the development process,
to accommodate more functions on board,
to enable new emerging technologies (e.g. multi-core processors, time and space partitioning, increased autonomy)
It is advisable to move towards an avionics architecture based on
composable building blocks where functional and timing
requirements, if possible, are addressed at component level
(separation of concerns).
ESA UNCLASSIFIED – For Official Use

17. Proposed Way Forward SOIS Services:
The introduction of the previously mentioned SOIS standardised
services supports this approach allowing to decouple the functional and
timing requirements strictly related to the communication protocols
from the ones related to the device access protocols and again from
the ones related to the applications algorithms.
These concepts will be briefly discussed for:
Sub-Network Services
Command & Data Acquisition Services
Message Transfer Service.
ESA UNCLASSIFIED – For Official Use

18. Sub-Network Services Characterisation
Low level communication req. can be captured in the sub-network layer to define the bus profile and to expose to the upper layers of the flight software functional and non-functional attributes of the services primitives.
Sub-Network Service Primitives
Bus Protocol
Bus Profile
AOCS Frequency
Sensor Max Latency
Command Accuracy
Sensor Access Time
Equipment Physical Address
Bus Bandwidth Allocation
Equip. Physical Address
Actuators Access Time
AOCS Algorithm Duration
Service Time and Functional Characterisation
Traffic Scenario for the Nodes
ESA UNCLASSIFIED – For Official Use

19. Command & Data Acquisition Services Characterisation
The requirements related to the mechanisms to access the on-board devices can also be isolated within the C&DA services group, mainly in DAS and DVS.
Sub-Net Service Timing
Raw Data Format
Common Data Dictionary
Device Access Req.
Calib. Curves
Engineering Data Format
Device Required Interface
Electronic Data Sheet
Device Virtualisation Service
Device Access Service
Device Enumeration Service
Service Time and Functional Characterisation
Raw Command/Acquisition Sequence
The services can be automatically configured and instantiated during the design phase based on the description of the EDS and provide a well characterised and standardised interface.
ESA UNCLASSIFIED – For Official Use

20. Message Transfer Service Characterisation
In the Avionics System Reference Architecture, the Software Bus entity is in charge to support the communication between applications and SW components.
Although the Software Bus can be implemented with different mechanisms, it is clear that the SOIS MTS provides the needed infrastructure.
Message Transfer Service Primitives
Asynchronous Message Transfer Service Protocol
Registration Table
APID Definition
TM/TC Formats
Tasks Deadlines
External Nodes Routing
PUS Services
Service Time and Functional Characterisation
Message Traffic with Local and Remote SW Entities
Sub-Net Service Timing
ESA UNCLASSIFIED – For Official Use

21. Flight Software using SOIS Services
ASW tasks schedule and I/O schedule are now related each others only due to the AOCS dependencies and the I/O operations are represented in terms of services (SOIS request & indication, time events).
Components can be designed independently according to the functional and non-functional attributes of the interfaces.
ASW Time Domain
Payload 2 Manager
OBCP Interpreter
MTL Manager
TC Manager
SOIS C&DA
AOCS
SOIS C&DA
Payload 1 Manager
Science TM Processing
Scrubbing
HK TM Processing
SOIS FPSS
EEPROM Manager
Monitoring
Mode Manager
Bus Time Domain
SOIS Sub-Network
SOIS Sub-Network
SOIS Sub-Network
SOIS Sub-Network
SOIS Sub-Network
SOIS Sub-Network
AOCS
Acquisitions
Payload 1
Acquisitions
Payload 2
Commanding
AOCS
Commanding
Large Data Transfer
Payload 2
Acquisitions
Minor Frame 0
(125 msec)
Minor Frame 1
(125 msec)
Minor Frame 2
(125 msec)
Minor Frame 3
(125 msec) …
Minor Frame 6
(125 msec)
Minor Frame 7
(125 msec) t
Major Frame (1 sec)
ESA UNCLASSIFIED – For Official Use

22. Improvements to Flight Software
Some of the beneficial effects of the introduction of
standard services:
the possibility to develop and analyse the software applications/components based on clear interfaces
the possibility to deploy some of the applications on a different processing core or partition without impacting the design of the avionics system
the possibility to exchange software/hardware components (e.g. sub-network services) with minimal impacts to the overall design.
ESA UNCLASSIFIED – For Official Use

23. Status of SOIS publications and related developments
ESA UNCLASSIFIED – For Official Use

24. Status of SOIS documentation
SOIS Sub-Network Services:
published in 2009 and are currently used to drive new and upgraded ECSS protocols for CAN and Spacewire.
SOIS Application Support Services:
Time Access Service published in 2011
File and Packet Store Service and Message Transfer Service are currently under Agency review and will be published in 2011
C&DA services are planned for 2011/2012
CCSDS SOIS work is now concentrated on:
the refinement of the communication architecture, particularly in terms of addressing and the provision of software APIs
The use of electronic data sheets to automate the process of interface definition and integration (C&DA and DES)
ESA UNCLASSIFIED – For Official Use

25. Present and Future Developments
Ongoing activities supporting standardisation:
A SOIS prototype is presently being prepared by SciSys (UK) in collaboration with ASTRIUM (F). This will result in an upgraded RASTA system at ESTEC and a published set of IPR free API’s.
A prototype of the CCSDS file transfer protocol (CFDP) mapped to an implementation of the SOIS file and packet store services is being prepared by Spacebel (B). This will also result in an upgraded RASTA system.
Packet Store Services have also implemented by Scisys (UK) in the frame of the MARC project.
An ECSS standard for CAN Bus is under preparation. This is being driven by the Exomars program and will result in an IP core compatible with SOIS sub-network services.
A SOIS/ECSS software component for Mil1553 Bus Controller has been developed by RUAG (S) and its counter part for Remote Terminal Units is being implemented. These software building blocks are produced in compliance with the flight software ECSS standards and validated on the RUAG’s flight hardware platforms (Tiger and Panther boards).
An alternative SOIS/ECSS sub-network services implementation for Mil1553 Bus Controller have been developed by Terma (DK) and integrated in the Avionics System Test Bench at ESA.
On 2011 the following additional activities are planned:
A TRP activity exploring the use of Electronic Data Sheets.
A TRP activity demonstrating Plug and Play techniques.
A TRP activity proving an end-to-end test-bed for the evaluation of file based communication and operations.
ESA UNCLASSIFIED – For Official Use

26. Conclusions
ESA UNCLASSIFIED – For Official Use

27. On-board time =SOIS TAS Libraries: mathematical, etc.
Conclusions 1/2
The key characteristics of the SOIS services architecture have been presented.
It has been shown that some of the essential features of the Execution Platform in the Avionics System Reference Architecture can be specified and implemented using the SOIS services.
Execution platform
BSP
SOIS Sub-Network
Container services
Connector services
PUS specific
Component services
Abstract component services
PUS and MTL services
OBCP
interpreter
SOIS C&DA
PUS monitoring
RTOS
Context
Mgmt
On-board time =SOIS TAS
SOIS MTS
Libraries: mathematical, etc.
EDS
Bus Profile
Reg Table
ESA UNCLASSIFIED – For Official Use

28. Conclusions 2/2
Some services have been discussed in the context of the avionics and flight software design phase, here the flexibility given by these services demonstrates to be very beneficial as it allows to characterise the service interfaces without modifying the primitives.
A number of prototypes and flight software developments are ongoing under ESA contracts and in the near future will allow consolidate further the CCSDS standard specifications.
ESA UNCLASSIFIED – For Official Use

29. SOIS and Software Reference Architecture
F. Torelli DASIA Malta 17/05/2011
ESA UNCLASSIFIED – For Official Use