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Prototyping of CCSDS SOIS services on 1553 Bus. Sev Gunes-Lasnet, Olivier Notebaert Astrium Satellites – Data Processing & Advanced studies – ASG74. 1553 SOIS subnetwork services prototyping and porting logic . Prototyping & porting feedback. - PowerPoint PPT Presentation
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CCSDS SOIS Working Group Meeting – Berlin, Germany14th of October 2008
Prototyping of CCSDS SOIS services on 1553 Bus
Sev Gunes-Lasnet, Olivier NotebaertAstrium Satellites – Data Processing & Advanced studies – ASG74
15/01/2007 p2
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Astrium Satellites Prototyping of CCSDS SOIS services on 1553 busCCSDS SOIS WG Berlin 2008
1553 SOIS subnetwork services prototyping and porting logic
SOIS subnetwork
1553 services
Rastadrivers
SCoC3 Simulator RASTA platformIP 1553 Gaisler
(Actel core)
SOIS subnetwork
SpW services
Specifications
subnetworkservices
Drivers 1553For SCoC
SOIS greenand
Red books
ECSS-E-50-13 (1553)
Tailored
ECSS -E-40
External input SciSys input Astrium input
Drivers 1553 Drivers SpW Porting to RASTA by SciSys
Inputs
Synchronisation
Test service Packetservice
Memoryaccessservice
Devicediscovery
SOIS subnetwork
services
Referenceuse case
Development
15/01/2007 p3
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Astrium Satellites Prototyping of CCSDS SOIS services on 1553 busCCSDS SOIS WG Berlin 2008
Prototyping & porting feedback The SOIS sub-network services layer has been
developed and validated on the SCoC3 platform SCoC3 is a Spacecraft Controller on a Chip which includes a
LEON3 processor and I/O systems for 1553, SpW and Can. It has then been ported on the on the RASTA platform
The RASTA platform is part of the ESA reference avionics facility test bench allowing to prototype on-board data handling space applications
The same set of services is supported for the Bus Controller on both platforms
15/01/2007 p4
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Astrium Satellites Prototyping of CCSDS SOIS services on 1553 busCCSDS SOIS WG Berlin 2008
Prototyping & porting feedback Some implementation differences have been introduced
during the porting The origin for of such differences are:
Differences between the MIL-Std-1553B controllers used in SCoC3 and RASTA, in particular the functions accessible through their drivers
The absence of an accurate on-board long-range timer on RASTA while SCoC3 provides a built in HW timer in support of the bus protocol engine and synchronisation service
do not affect the nature of services but impacts: functions of the underlying communication protocol performance of the services
15/01/2007 p5
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Astrium Satellites Prototyping of CCSDS SOIS services on 1553 busCCSDS SOIS WG Berlin 2008
Prototyping & porting feedback Implementation differences on Synchronisation service:
For SCoC3 platform The distributed time data is retrieved from CCSDS Time Manager (CTM)
implemented inside SCoC3. It provides a time conform to CCSDS CUC Time format, i.e. a range of 232
second with a precision of 0.5x 2-24 seconds This complies to the ECSS-E-50-13 Standard
For Rasta platform The distributed time data is retrieved from the on-board Leon Timer. Software managed clock ticks are used to support the time service. The range and precision of the time depend on the clock ticks
configuration. In our RTEMS configuration, the effective range of the time is about 4000
seconds and the effective precision is 10 ms.
15/01/2007 p6
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Astrium Satellites Prototyping of CCSDS SOIS services on 1553 busCCSDS SOIS WG Berlin 2008
Prototyping & porting feedback: Implementation differences on bus profiling:
For SCoC3 platform The HW clock signal generated by the CTM is used to automatically drive
the cyclical 1553 Communication frame The clocks are also used to control message sending time inside such
frames, allowing the definition and utilisation of time intervals. For RASTA platform
there is no HW support which can be used to drive the communication frame and message sending. Instead, the software managed timer generates cyclic events, used to launch each communication frame.
This method does not provide the same stability of the cycle duration. The messages inside a communication frame are transmitted without time
control, i.e. they are sent one after another without delay between them. The definition and exploitation of time intervals as defined in ECSS
standard is not really possible.
15/01/2007 p7
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Astrium Satellites Prototyping of CCSDS SOIS services on 1553 busCCSDS SOIS WG Berlin 2008
Prototyping & porting feedback: performance
As a result, key elements driving the SOIS subnetwork services performance over MIL-STD-1553 have been identified :
Theoretically, both platforms have similar HW elements to support the sub-network services in a similar way, as each of them integrates a Mil-Std-1553B compliant controller
But several points shall be considered for the performance of a specific implementation of the services on a dedicated platform
15/01/2007 p8
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Astrium Satellites Prototyping of CCSDS SOIS services on 1553 busCCSDS SOIS WG Berlin 2008
Prototyping and porting feedback:performance
key elements driving the SOIS subnetwork services implementation performance over MIL-STD-1553:
Bus Controller integration inside the platform, are any features disabled ?
External clock to be used for the bus controller for its synchronisation or message handling
Availaibility of software driver allowing to enhance functional features for the use of the Bus Controller
How about the cost in term of CPU and memory consuming when using such driver ?
15/01/2007 p9
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Astrium Satellites Prototyping of CCSDS SOIS services on 1553 busCCSDS SOIS WG Berlin 2008
Drivers related topics (1/2) SCoC3 runs with a driver for IP1553 provided by Astrium.
All functional features necessary to support the sub-network services and the ECSS protocol are available through this driver.
For RASTA platfom, we use a driver for Actel Core1553BRM Driver distributed by Gaisler Research with its RTEMS distribution. The functions provided by this driver do not cover all features of the Actel
Core1553BRM. For instance, no support to perform timing control of messages handling is provided
15/01/2007 p10
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Astrium Satellites Prototyping of CCSDS SOIS services on 1553 busCCSDS SOIS WG Berlin 2008
Drivers related topics (2/2) The driver for IP1553 is developed for space on-board software and
adapted for such application For instance, the API and related data structures are defined so that its use is
as easy as possible and its CPU consuming is minimized. In addition, error handling is considered.
The driver for the Actel Core1553BRM, can be considered as in a prototype form.
It provides minimum access to 1553 functions without optimisation It is used as IO device driver, so that it uses standard IO system call, like open,
close, ioctl. Such design introduces an overhead in term of service processing.
The data structures used by the API for its BC message is in a format neither as true 1553 message nor as a data format directly suitable for Actel Core1553BRM controller
Such data structure definition obviously introduces an overhead of the processing on the service using it.
The error handling is in a simple form. Some bugs still exist in the drivers.
15/01/2007 p11
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Astrium Satellites Prototyping of CCSDS SOIS services on 1553 busCCSDS SOIS WG Berlin 2008
Prototyping & porting feedback Preliminary feedback on SOIS :
Status failure and status success SOIS requires a Success Status without an error code This is not enough for most 1553 based applications which require that a
detailed error 1553 status must go back up to user level (so as to be treated by the FDIR application).
The feedback from 1553 users would claim for an error report delivery to the user of the SOIS subnetwork service
This is implemented on ECSS-1553 Standard through an OR of all status words involved in the 1553 messages supporting the service
15/01/2007 p12
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Astrium Satellites Prototyping of CCSDS SOIS services on 1553 busCCSDS SOIS WG Berlin 2008
Preliminary feedback on SOIS services
About the retry function included in the 1553 standard The ECSS standard does not use the built-in retry function; Therefore, our reference implementation does not map on the standard
1553 message retry in support of the SOIS guaranteed and assured quality of service
SOIS Packet Transfer service implementation can map on the ECSS verified length QoS of the ECSS Data Block Transfer
This allows upper level (on network management) to manage the retry function for mapping on the SOIS QoS
The messages status could also be used at upper layers to transmit the information on bus errors in support of a retry function
15/01/2007 p13
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Astrium Satellites Prototyping of CCSDS SOIS services on 1553 busCCSDS SOIS WG Berlin 2008
Preliminary feedback on SOIS services
Synchronisation issue The SOIS communication view is mostly asynchronous
Data is fetched upon need – network should be hidden to the user who should not have to care how it is fetched on the data link to end terminal
1553 systems use mostly synchronous protocols(Such as the one described in ECSS-E-50-13)
The delay between Synchronisation and actual data acquisition/command on the end terminal sensor/actuator defines the real-time performance (e.g. latency, jitter…) of the data transfer
The SOIS end-to-end service performance will depend on the coupling of the user calls with the 1553 synchronisation service.
Users having high determinism and time accuracy requirements (mostly command/control and dependable systems in general) will require such coupling
15/01/2007 p14
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Astrium Satellites Prototyping of CCSDS SOIS services on 1553 busCCSDS SOIS WG Berlin 2008
Preliminary feedback on SOIS services
Prototyping & porting feedback preliminary conclusions All SOIS Subnetwork services have been implemented and
verified on the MIL-Std-1553B bus using two different MilBus coupling systems
Performance of the system is being assessed End-to-end real-time performance of SOIS services on 1553
bus is tightly linked to the implementation of synchronisation between user and the bus system
Overhead due to HW/SW drivers are much more significant than those introduced by the SOIS layered architecture
SOIS subnetwork services should include a interface to report 1553 Status to the user (or to the network management)