Overview of my student placement

April 20, 2023

Philipp Spliethoff

Overview of my student placement

Placement Overview2

Agenda

SOIS Proof of Concept – File Store ServiceBasic OverviewSpecific implementationsDocumentation

XtratuMContext Analyser

Placement Overview3

Spacecraft Onboard Interface Services (SOIS)

Placement Overview4

SOIS – Overview

Standardised Interfaces of spacecraft equipment by specifying well-defined serviceAbstracting subnetworks of the spacecraftThree service layers:

Application Support Layer servicesProvide common capabilities needed onboardUse subnetwork layer services (locally or remotely)

Transfer Layer servicesSubnetwork Layer services

Associated with one underlying data linkMapped to best possible extend (using convergence functions)

Defined by the Consultative Committee for Space Data System (CCSDS)

Placement Overview5

Spacecraft Onboard Interface Services

Com

munication M

anagement

Cmd & DataAcquisitionServices

TimeAccessService

File &Packet Store

Services

MessageTransferService

DeviceEnumeration

Service

PacketService

MemoryAccessService

SynchronisationService

DeviceDiscoveryService

TestService

Datalink Convergence Protocols

ApplicationLayer

ApplicationSupport Layer

TransferLayer

SubnetworkLayer

Network Protocol

Transport Protocol

Milbus SpaceWire CAN Wireless

MissionSpecific

Applications

Placement Overview6

SOIS – Benefit

Reusability of user-applicationsIndependent development of s/w and h/w (stable subnetworks)Core servicesPorting subsystems and payload across missions

reduced development time and cost

Placement Overview7

Spacecraft Onboard Interface Services Proof of Concept

File Store Service

Placement Overview8

SOIS File Store Service

The SOIS File Store Services provide a standard interface to allow onboard software to request:

access to files resident in a file storemodifications to files in a file storemanagement of files within a file store (e.g., create, delete, rename)

Split into File Access Service and File Management Service

Placement Overview9

SOIS FSS – File Access Service Primitives

Open a fileClose a fileRead from a fileWrite to a fileOptional:

Seek to an Offset of a file

Easy to implement

One-to-one wrapping on POSIX system calls (open, close, lseek etc.)

Placement Overview10

SOIS FSS – File Management Service Primitives

list the contents of a directorycopy and move filescreate and delete files.Optional features:

create, rename and delete directoriesget and change the user entity’s current directoryrename fileslock or unlock fileslist the currently locked filesfind a file within a file storeget the status of a file


SOIS File Store Service

SSMMproviding flat Memory I/FOBC

File andPacketStoreServices

Remote File System

UserApplications

Subnetwork Packet Service

Network File and Packet Store Access Protocols

File and PacketStore System


Network File and Packet Store Access Protocols

Subnetwork-Specific Packet Protocol


Service Primitives

SSMMproviding flat Memory I/F

Remote BlockStorage Protocol



Remote BlockStorage Protocol



Data Storage

Block Access

Example Deployment of the SOIS File Store Service using multiple Distributed Mass Memories


SOIS FSS – My Implementation

RTEMS LibraryHighly Configurable (at build time) through pre-processor directivesImplements all features defined by the SOIS (minimal and optional)AVL Tree added to global utility repositorynon-deterministic state machine to evaluate wildcard expressionsDocumented using Doxygen


SOIS FSS – Implementation

Based on:RTEMS 4.8RTEMS In Memory File System (IMFS)Direct Function Calls

Can easily be advanced to use network protocol

OBC

FileStoreServices

UserApplications

Network File Store Access Protocols

File Store System

Direct Function Call acting as Underlying Transport

Network File Store Access Protocols

Service Primitives

Data Storage

Block Access

IMFS


SOIS FSS – Function Implementation

Direct wrapper functions to all POSIX compatible FSOpen, Close, Read, Write, Seek, CreateFile, DeleteFile, CreateDir, DeleteDir

Implementation through combination of existing POSIX function

ListDirectory, CopyFile, MoveFile, MoveDir

Additional mechanism neededGetWorkingDirectory, RenameDir, FindFile, FileLocks(Lock/UnlockFile, ListLockedFiles…)

MoveDir is not defined by SOIS FSS, implements RenameDir through use of POSIX calls (rename() is broken in RTEMS 4.8)


SOIS FSS – Locking

Lock unopened filesLocks restrict access to the fileLock types:

lock-owner read-only access, all other user entities no accesslock-owner read-only access, all other user entities read-only accesslock-owner read-write access, all other user entities no access

No native locking from file systemNo way to check if a file is opened

Possible Solutions:1. POSIX chmod() to change access rights according to the lock2. Create lock files on the file system3. Use a internal structure to store information about locks


SOIS FSS – Locking Design


Util – AVL Tree

Self balancing binary search treeSearch in log(n) timeFast lookupBalancing done when item is inserted/deleted (log(n) time)

Operations:InsertDeleteFindInorder Walk (e.g. print content sorted

A

E

B

D

C

E

A

E

B

D

C

E

A

EB

D

C F

Insert Sequence: A, B, C, D, E, F

Binary Tree AVL Tree

A

E

B

D

C

E

A

E

B

D

C

E

A

EB

D

C F


SOIS FSS - FindFile

SOIS recommends using wildcards to match file namesnon-deterministic finite state machine to evaluate wild card characters to represent the expressionComparison between a filename and the machine in linear timePossible characters: *, +, ?, {, }


State machine

State machine for “a*c?d+e”


Documentation

Doxygen


Doxygen

Generate documentation from comments in source filesLanguages: C++, C, Java, Objective-C, Python, IDL (Corba and Microsoft flavors), Fortran, VHDL, PHP, C#, and to some extent D Output as HTML, Latex, rtf, PS, PDF, Man-PagesHighly configurableOpen Source and licensed under GNU GPL

Documentation is not affected by GPL

Internal PreprocessorEasy switch between different Documentation version (e.g. customer and internal version)


Doxygen – HTML Output Sample


XtratuM


XtratuM - Overview

Hypervisor for embedded systems enabling partitioningFree and Open Source (GPLv2)

Applications on top don’t derive that

Developed for leon2Able to run RTOS like RTEMS or Linux

Target:Get it working on leon3Test features


XtratuM - Conclusion

Easy to set upHardware and partitions are defined in a XML fileDocumentation is availablecreated Detailed xml file description

<CyclicPlanTable><Plan id="0" majorFrame="10s">

<Slot id="0" start="0ms" duration= "5s" partitionId="0"/><Slot id="1" start="5s" duration= "1s" partitionId="1"/><Slot id="2" start="6s" duration= "500ms" partitionId="2"/><Slot id="3" start="6500ms" duration= "100ms" partitionId="3"/><Slot id="4" start="6700ms" duration= "50ms" partitionId="4"/><Slot id="5" start="6800ms" duration= "10ms" partitionId="5"/><Slot id="6" start="6900ms" duration= "5ms" partitionId="6"/><Slot id="7" start="6950ms" duration= "1ms" partitionId="7"/><Slot id="8" start="7000ms" duration= "2s" partitionId="8"/>

</Plan></CyclicPlanTable>


XtratuM - Conclusion

Features:IPC restricted by Partition hierarchy and definition

XAL – Basic C supportRTEMS – is available, but I didn’t test itAltenatives:

LithOSPaRTiKle (GPLv2)


Context Analyser


Context Analyser

Get real timing information about RTEMS tasks running on hardware

Approach:Output Task ID to IO pins of the RASTA/FPGA-Board

Inserted code into the RTEMS source code to output the ID


Context Analyser

Result:Works with OscilloscopeLogic Analyser is ordered

Documents

Overview of my student placement