Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The Linux operating system and shared Ethernet are alternative technologies with the potential to
reduce both the development time and costs of satellites as well as the supporting infrastructure.
Modular satellites, ground stations and rapid proto typing testbeds also have a common
requirement for distributed real-time computation. The identified technologies were investigated
to determine whether this requirement could also be met.
Various real-time extensions and modifications are currently available for the Linux operating
system. A suitable open source real-time extension called Real-Time Application Interface
(RTAI) was selected for the implementation of an experimental distributed real-time system.
Experimental results showed that the RTAI operating system could deliver deterministic realtime
performance, but only in the absence of non-real-time load.
Shared Ethernet is currently the most popular and widely used commercial networking
technology. However, Ethernet wasn't developed to provide real-time performance. Several
methods have been proposed in literature to modify Ethernet for real-time communications. A
token passing protocol was found to be an effective and least intrusive solution. The Real-Time
Token (RTToken) protocol was designed to guarantee predictable network access to
communicating real-time tasks. The protocol passes a token between nodes in a predetermined
order and nodes are assigned fixed token holding times. Experimental results proved that the
protocol offered predictable network access with bounded jitter.
An experimental distributed real-time system was implemented, which included the extension of
the RTAI operating system with the RTToken protocol, as a loadable kernel module. Real-time
tasks communicated using connectionless Internet protocols. The Real-Time networking (RTnet)
subsystem of RTAI supported these protocols. Under collision-free conditions consistent
transmission delays with bounded jitter was measured. The integrated RTToken protocol
provided guaranteed and bounded network access to communicating real-time tasks, with limit
overheads. Tests exhibited errors in some of the RTAI functionality. Overall the investigated
technologies showed promise in being able to meet the distributed real-time requirements of
various applications, including those found in the satellite environment. / AFRIKAANSE OPSOMMING: Die Linux bedryfstelsel en gedeelde Ethernet is geïdentifiseer as potensiële tegnologieë vir
satelliet bedryf wat besparings in koste en vinniger ontwikkeling te weeg kan bring. Modulêr
ontwerpte satelliete, grondstasies en ontwikkeling platforms het 'n gemeenskaplike behoefte vir
verspreide intydse verwerking. Verskillende tegnologieë is ondersoek om te bepaal of aan die
vereiste ook voldoen kan word.
Verskeie intydse uitbreidings en modifikasies is huidiglik beskikbaar vir die Linux bedryfstelsel.
Die "Real-Time Application Interface" (RTAI) bedryfstelsel is geïdentifiseer as 'n geskikte
intydse uitbreiding vir die implementering van 'n eksperimentele verspreide intydse stelsel.
Eksperimentele resultate het getoon dat die RTAI bedryfstelsel deterministies en intyds kan
opereer, maar dan moet dit geskied in die afwesigheid van 'n nie-intydse verwerkingslas.
Gedeelde Ethernet is 'n kommersiële network tegnologie wat tans algemeen beskikbaar is. Die
tegnologie is egter nie ontwerp vir intydse uitvoering nie. Verskeie metodes is in die literatuur
voorgestelom Ethernet te modifiseer vir intydse kommunikasie. Hierdie ondersoek het getoon
dat 'n teken-aangee protokol die mees effektiewe oplossing is en waarvan die implementering
min inbreuk maak. Die "Real-Time Token" (RTToken) protokol is ontwerp om voorspelbare
netwerk toegang tot kommunikerende intydse take te verseker. Die protokol stuur 'n teken tussen
nodusse in 'n voorafbepaalde volgorde. Nodusse word ook vaste teken hou-tye geallokeer.
Eksperimentele resultate het aangedui dat die protokol deterministiese netwerk toegang kan
verseker met begrensde variasies.
'n Eksperimentele verspreide intydse stelsel is geïmplementeer. Dit het ingesluit die uitbreiding
van die RTAI bedryfstelsel met die RTToken protokol; verpak as 'n laaibare bedryfstelsel
module. Intydse take kan kommunikeer met verbindinglose protokolle wat deur die "Real-Time
networking" (RTnet) substelsel van RTAI ondersteun word. Onder ideale toestande is konstante
transmissie vertragings met begrensde variasies gemeet. Die integrasie van die RTToken
protokol het botsinglose netwerk toegang aan kommunikerende take verseker, met beperkte
oorhoofse koste as teenprestasie. Eksperimente het enkele foute in die funksionaliteit van RTAI
uitgewys. In die algemeen het die voorgestelde tegnologieë getoon dat dit potensiaal het vir
verskeie verspreide intydse toepassings in toekomstige satelliet en ook ander omgewings.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53699 |
| Date | 12 1900 |
| Creators | Rozendaal, A. (Abraham) |
| Contributors | Du Plessis, J. J., Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 138 p. : ill. |
| Rights | Stellenbosch University |
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