Performance analysis of Ethernet Powerlink protocol: Application to a new lift system generation

International audienceTo ensure control, present lifts use the Controller Area Network (CAN) bus for transmitting commands between components. Although it is largely adopted in the industrial process, CAN is not able to guarantee a sufficient throughput to transmit multimedia data or to meet the requirements of some safety standards. In this paper, we present a transition case from electrical/electromechanical components to a networked control system. The main element we focus on in the lift system is the safety chain. We propose to build the lift communication system around real-time Ethernet for more efficiency, smartness and safety. Furthermore, the use of the openSAFETY protocol as a safety layer over the real-time Ethernet allows the achievement of the required Safety Integrity Level (SIL). This adopted solution should meet the adopted standard IEC 61508 requirements

Coupling of a Powerline Communication Modem to an Industrial Fieldbus Network

In a broad and heterogeneous industrial communications environment, the need of having flexibility as well as maintaining the reliability and low cost has pushed the researchers to look for new possibilities and market opportunities to cover all the needs. Actual industrial systems are needed of at least two ways of inputs: power input, for the system operation, and data input for controlling, testing and administrating the system. The main restrictions, that actual systems and networks have, are low flexibility and, sometimes, considerable expenses in terms on maintenance. But also they have advantages, e.g. low response time, high reliability, wide and highly known architecture etc. In this background, grows the thought of increasing the flexibility without impacting such important aspects as response time or reliability. On the industrial communication protocols, Ethernet POWERLINK standard is one of the existing protocols in the market. Ethernet POWERLINK is a real-time industrial communication protocol based on Ethernet standard, which is used for controlling and commanding several sensors and actuators with high speed, time-synchronization and reliability, minimizing the global system latency. The main aim of this project is to reach a balanced solution by joining both power and data inputs in just one cable that allows an increase in the flexibility, as well as decrease in the maintenance costs, restraining the response time and achieving compatibility with a wide spread standard as is Ethernet.Puche Planells, J. (2014). Coupling of a Powerline Communication Modem to an Industrial Fieldbus Network. http://hdl.handle.net/10251/46618.Archivo delegad

Wieloplatformowy system zarządzania przełącznikiem Ethernetowym czasu rzeczwistego

Mestrado em Engenharia Electrónica e TelecomunicaçõesAo longo dos últimos anos, o agora onipresente protocolo Ethernet, embora não dotado de mecanismos eficazes de gestão de QoS, foi ganhando uma grande aceitação no campo das comunicações industriais. Esta crescente aceitação deveu-se, em grande parte, a novos protocolos, baseados em Ethernet (por exemplo, Profinet, Ethernet Industrial, etc), capazes de fornecer comunicações com garantias deterministas ou de tempo-real. O comutador Ethernet Hartes (Hard Real-Time Ethernet Switch), foi desenvolvido para disponibilizar uma infra-estrutura de comutação Ethernet capaz de fornecer garantias de pontualidade, de bom uso da largura de banda e para suportar, de modo eficiente, a flexibilidade operacional necessária em aplicações de tempo-real distribuídas, de sistemas embarcados dinâmicos. O desenvolvimento do comutador Hartes, foi baseado em trabalho anterior do paradigma de comunicação FTT (Flexible Time-Triggered), e teve por objetivo o projeto de um comutador Ethernet com melhor controlo de transmissão, escalonamento do tráfego e integração transparente de nodos não tempo-real. NetConf é uma tecnologia recente de gestão de redes que tem vindo progressivamente a substituir a tecnologia SNMP (Simple Network Management Protocol), o standard de facto há muito adoptado pela indústria. A maior diferença entre NetConf e o SNMP é que o NetConf adopta um mecanismo de comunicação baseado em XML-RPC, que, graças às ferramentas desenvolvidas no âmbito de outras tecnologias web, permite ciclos mais rápidos e mais simples de desenvolvimento e de gestão. O comutador Hartes não dispõe de uma plataforma de gestão com uma interface padronizada para os protocolos SNMP ou NetConf, de modo a permitir a sua gestão remota. Assim, o objetivo principal deste trabalho é o desenvolvimento de componentes-chave de apoio à gestão multiplataforma do comutador Ethernet Hartes, bem como a respectiva avaliação de desempenho dos componentes desenvolvidos.In recent years, the now ubiquitous Ethernet protocol that lacks effective QoS management functions, has gained momentum in the field of industrial communication, by means of novel, Ethernet-based protocols (e.g. Profinet, Industrial Ethernet, etc.), which are able to provide deterministic communications. HaRTES – Hard Real-Time Ethernet Switch, aimed to develop an Ethernet switching infrastructure, able to provide timeliness guarantees, efficient bandwidth usage and support for operational flexibility as required by dynamic real-time distributed embedded systems. The project was built upon previous work on the FTT (Flexible Time-Triggered) communication paradigm to develop Ethernet switches with enhanced transmission control, traffic scheduling, and transparent integration of non-real-time nodes. NetConf is a recent network management technology that is replacing the Simple Network Management Protocol (SNMP) – widely used and long adopted by industry standard. The biggest difference between NetConf and SNMP is that the former use a communication mechanism based on XML-RPC, which, thanks to the tools developed in the scope of other web technologies, allows a simpler and faster development and management cycle. The HaRTES project had not provided a management platform with a standardized interface for SNMP or NetConf protocols, enabling remote switch management. Thus the main objective of this work was to develop key components for the support of the standardized multiplatform management interfaces for the HaRTES switch and their performance assessment

CarRing IV- Real-time Computer Network

Ob in der Automobil-, Avionik- oder Automatisierungstechnik, die Fortschritte in der Echtzeitkommunikation richten sich auf weitere Verbesserungen bereits existierender Lösungen. Im Kfz-Bereich führen die steigenden Zahlen computerbasierter Systeme, Anwendungen und Anschlüsse sowie die Verwendung mehrerer proprietärer Kommunikationsstandards zu einem immer komplexeren Kabelbaum. Ursächlich hierfür sind inkompatible Standards, wodurch nicht nur die Kosten, sondern auch das Gewicht und damit der Kraftstoffverbrauch negativ beeinflusst werden. Im ersten Teil der Dissertation wird das Echtzeitprotokoll von CarRing IV (CRIV) vorgestellt. Es bietet isochrone und harte Echtzeitgarantien, ohne dass eine netzwerkweite Synchronisation erforderlich ist. Mit bis zu 16 Knoten pro Ring kann ein CR-IV-Netz aus bis zu 256 Ringen bestehen, die durch Router miteinander verbunden sind. CR-IV verwendet ein reduziertes OSI-Modell (Schichten 1-3, 7), das für seine Anwendungsbereiche sowohl typisch als auch vorteilhaft ist. Außerdem unterstützt es sowohl ereignis- als auch zeitgesteuerte Kommunikationsparadigmen. Der Transparent-Modus ermöglicht es CR-IV, als Backbone für bestehende Netze zu verwenden, wodurch Inkompatibilitätsprobleme beseitigt werden und der Wechsel zu einer einheitlicheren Netzlösung erleichtert wird. Mit dieser Funktionalität können Nutzergeräte über ein CR-IV-Netz miteinander verbunden werden, ohne dass der Nutzer eingreifen oder etwas ändern muss. Durch Multicast unterstützt CRIV auch die Emulation von Feldbussen. Der zweite Teil der Dissertation stellt den anderen wichtigen Aspekt von CR-IV vor. Alle Schichten des OSI-Modells sind in einem FPGA mit Hardware Description Languages (HDLs) ohne Hard- oder Softprozessoren implementiert. Das Register-Transfer-Level (RTL)-Hardwaredesign von CR-IV wird mit einem neuen Ansatz erstellt, der am besten als tokenbasierter Datenfluss beschrieben werden kann. Der Ansatz ist sowohl vertikal als auch horizontal skalierbar. Er verwendet lose gekoppelte Processing Elements (PEs), die stateless arbeiten, sowie Arbiter/Speicherzuordnungspaare. Durch die granulare Kontrolle und die Aufteilung aller Aspekte einer Lösung eignet sich der Ansatz für die Implementierung anderer Software-Level-Lösungen in Hardware. Viele Testszenarios werden durchgeführt, um die in CR-IV erzielten Ergebnisse zu verdeutlichen und zu überprüfen. Diese Szenarien reichen von direkten Leistungsmessungen bis hin zu verhaltensspezifischen Tests. Zusätzlich wird eine Labor-Demo erstellt, die grundsätzlich auf ein Proof of Concept zielt. Die Demo stellt einen praktischen Test anstelle szenariospezifischer Tests dar. Alle Testszenarien und die Labor-Demo werden mit den Prototyp-Boards des Projekts durchgef¨uhrt, d.h. es sind keine Simulationstests. Die Ergebnisse stellen die realistischen Leistungen von CR-IV mit bis zu 13,61 Gbit/s dar.Whether be it automotive, avionics or automation, advances in their respective real-time communication technology focus on further improving preexisting solutions. For in-vehicle communication, the ever-increasing number of computer-based systems, applications and connections as well as the use of multiple proprietary communication standards results in an increasingly complex wiring harness. This is in-part due to those standards being incompatible with one another. In addition to cost, this also impacts weight, which in turn affects fuel consumption. The work presented in this thesis is in-part theoretical and in-part applied. The former is represented by a new protocol, while the latter corresponds to the protocol’s hardware implementation. In the first part of the thesis, the real-time communication protocol of CarRing IV (CR-IV) is presented. It provides isochronous and hard real-time guarantees without requiring network-wide clock synchronization. With up to 16 nodes per ring, a CR-IV network can consist of as many as 256 rings interconnected by routers. CR-IV uses a reduced OSI model (layers 1-3, 7), which is both typical of and preferable for its application areas. Moreover, it supports both event- and time-triggered communication paradigms. The transparent mode feature allows CR-IV to act as a backbone for existing networks, thereby addressing incompatibility concerns and easing the transition into a more unified network solution. Using this feature, user devices can communicate with one another via a CR-IV network without requiring user interference, or any user device or application changes. Combined with the protocol’s reliable multicast, the feature extends CR-IV’s capabilities to include field bus emulation. The second part of the thesis presents the other important aspect of CR-IV. All of its OSI model layers are implemented in a FPGA using Hardware Description Languages (HDLs) without relying-on or including any hard or soft processors. CR-IV’s Register-Transfer Level (RTL) hardware design is created using a new approach that can best be described as token-based data-flow. The approach is both vertically and horizontally scalable. It uses stateless and loosely coupled Processing Elements (PEs) as well as arbiter/memory allocation pairs. By having granular control and compartmentalizing every aspect of a solution, the approach lends itself to being used for implementing other software-level solutions in hardware. Many test scenarios are conducted to both highlight and examine the results achieved in CR-IV. Those scenarios range from direct performance measurements to behavior-specific tests. Moreover, a lab-demo is created that essentially amounts to a proof of concept. The demo represents a practical test as opposed to a scenariospecific one. Whether be it test scenarios or the lab-demo, all are carried-out using the project’s prototype boards, i.e. no simulation tests. The results obtained represent CR-IV’s real-world realistic outcomes with up to 13.61 Gbps

Industriella realtidsethernet för maskinautomation

During the last two decades, Ethernet has become the de facto standard in office level networks. There are several motivations for using Ethernet also in control networks, including the abundance of low cost components, the high data transfer rates and the possibility of vertical integration with other networks of the organization. The first in­dustrial implementation of Ethernet was for communication between different devices on the controller level. Modern real-time industrial Ethernet technologies, like the ones studied in this thesis, have brought Ethernet also down to the field level. The thesis is divided into two sections. The first section contains presentations of the seven most used real-time industrial Ethernet technologies. The second section contains a more thorough study of EtherCAT, the one of the seven technologies that promise the best real-time performance. The main goals are to provide a review of the different tech­nologies available and to study the suitability of EtherCAT in the control networks of machine automation systems. In the first section, different real-time industrial Ethernet technologies are divided into three groups based upon how much they differ from standard office Ethernet. It is found that the technologies built entirely upon standard office Ethernet do in them­selves not promise any real-time capabilities. Their biggest weakness is the slow pro­cessing of the software communication protocol stack. The technologies that use stan­dard Ethernet hardware but dedicated software are good for soft real-time applications, but the lack of accurate synchronization between the devices makes them unsuitable for applications demanding hard real-time behavior. The technologies that use both special hardware and software offer superior real-time performance but are not as open to inte­gration with standard office Ethernet networks as the other solutions. The second section of the study contains three parts. In the first of them, a small test system is built to examine the suitability of EtherCAT for the closed loop control of a variable alternate current (AC) drive. In the second part, the availability of open source initiatives concerning EtherCAT is explored. In the third part, the possibility for master device redundancy in EtherCAT is investigated. The study indicates that EtherCAT achieves the short communication cycle times and accurate synchronization promised. Short cycle times are indeed needed as direct communication between slave devices is not supported in EtherCAT and thus the efficiency of the communication is almost totally dependent on the cycle time. EtherCAT networks are relatively easy to configure and maintain as there are comprehensive software suites available, both as commercial pro­grams and open source initiatives and for a variety of different operating systems. The least developed feature of EtherCAT proved to be the support for master device redun­dancy. Solutions for master redundancy are available, but more as concepts than as ready-to-use features. /Kir10Under de senaste två decennierna har Ethernet blivit något av en de facto standard för nätverk i kontorsmiljö. Det finns flera motiv för att använda Ethernet även i kontroll­nätverk, bland andra god tillgång av billiga komponenter, hög dataöverföringshastighet och möjligheter för vertikal integration med nätverk på andra nivåer av organisationen. Den första industriella tillämpningen av Ethernet var för kommunikation mellan olika kontrollenheter. Moderna realtidslösningar för industriella Ethernet-nätverk har fört Ethernet också ner till fältnivå. Det här diplomarbetet är uppdelat i två delar. Den första delen innehåller presen­tationer av de sju mest använda realtidslösningarna för industriella Ethernet-nätverk. Den andra delen innehåller en mer djupgående studie av EtherCAT, den av de sju lösningarna som utlovar bäst realtidsprestanda. De mest centrala målen är att ge en över­syn av de olika realtidslösningarna som finns tillgängliga för industriella Ethernet-nätverk samt att undersöka hur lämpligt EtherCAT är som kontrollnätverk för maskin­automation. Inledningsvis delas de olika lösningarna in i tre grupper på bas av hur mycket de skiljer sig från vanliga kontorsnätverk. Det visar sig att de lösningar som helt bygger på samma teknik som används i kontorsnätverk i sig själva inte kan utlova någon som helst realtidskapacitet. Deras största svaghet är den resurskrävande behandlingen av de kommunikationsprotokoll som används i kontorsnätverk. Det är dock möjligt att konstruera lösningar med relativt bra realtidsbeteende utgående från de här lösningarna bara man väljer rätt Ethernet-komponenter och tillräckligt kraftfulla mikroprocessorer i nätverksstationerna. De lösningar som använder vanlig Ethernet-maskinvara men egen programvara är bra för mjuka realtidssystem, men de brister i synkroniseringen mellan enheterna och är sålunda inte tillräckligt deterministiska för hårda realtidssystem. De lösningar som använder både egen hårdvara och egen mjukvara erbjuder överlägsen realtidsprestanda som öppnar nya möjligheter för effektivare reglering av olika system. Å andra sidan är de här lösningarna inte lika öppna för integration med vanliga kontorsnätverk som de lösningar som har mer likheter med vanliga kontorsnätverk. Den andra delen av studien inriktar sig på EtherCAT. EtherCAT är ett så kallat master/slave-nätverk, det vill säga att en av stationerna i nätverket styr kommuni­kationen och de andra i allmänhet inte själva kan initiera någon form av kommuni­kation. Den mest centrala funktionsprincipen för EtherCAT är att de olika slav-stationerna logiskt är ordnade i en kedja och att alla meddelanden passerar genom alla slav-stationer och blir också lästa och skrivna till av flera slav-stationer. I relativt små nätverk betyder det här att det bara skickas ett meddelande per kommunikationscykel. Meddelandena hanteras av speciell hårdvara i slav-stationerna och detta sker så snabbt att meddelandena bara blir fördröjda med bråkdelen av en mikrosekund. Master-stationen, däremot, är oftast konstruerad utan speciell hårdvara och består vanligen av en PC med realtidsoperativsystem och speciell mjukvara, ett så kallad EtherCAT master-program. Det att mastern består av standard Ethernet hårdvara betyder att den har relativt dålig timing-kapacitet. Därför är de olika slav-enheterna i ett EtherCAT nätverk i stället vanligen synkroniserade efter den första slav-enheten i kedjan. En synkroniseringsexakthet på mycket bättre än en mikrosekund utlovas och den kan användas både till att åstadkomma reaktioner på en exakt given tidpunkt och exakta tidsangivelser för när ett processvärde är uppmätt. Studien av EtherCAT är indelad i tre avsnitt. I det första av dem byggs ett litet testsystem för att undersöka hur lämpligt EtherCAT är som kontrollnätverk för återkopplad styrning av en frekvensomriktare. Den viktigaste enskilda egenskapen som krävs av ett kommunikationsnätverk för den här tillämpningen är att frekvensomriktaren ofta och snabbt får korrekt information om drivaxelns position. Det är också viktigt att positionsangivelserna är ackompanjerade av exakt information om när de är uppmätta. Studien visar att det är möjligt att uppnå båda de här egenskaperna med hjälp av EtherCAT. Det att direkt kommunikation mellan slav-stationerna i ett EtherCAT-nätverk inte understöds medför visserligen att överföringen av positions­datan tar två kommunikationscykler i anspråk, men eftersom det är möjligt att uppnå cykel­tider så korta som 133 µs torde prestandan i alla fall räcka för de flesta system. Det här medför dock att cykeltiderna måste hållas låga även om systemet i övrigt inte skulle kräva det. I det andra avsnittet undersöks tillgången på öppen källkodsbaserad programvara för EtherCAT. Det krävs ingen licens för att utveckla EtherCAT master-programvara, så det finns en mängd olika program för flera olika operativsystem på marknaden. Ett par av dem är baserade på öppen källkod. Ett av de mest intressanta är EtherLAB från Ingenieurgemeinschaft IgH. Det är i huvudsak utvecklat för Linux och innehåller förutom master-programvaran även mjukvara för diagnostik och för att generera kontrollrutiner från modeller skapade med Matlab/Simulink. I det här avseendet är det till och med kraftfullare än den mest använda kommersiella programvaran för EtherCAT, TwinCAT från Beckhoff Automation, som igen körs under MS Windows. I det tredje avsnittet granskas möjligheterna att duplicera den enhet som styr ett EtherCAT nätverk, så kallad master-redundans. Studien presenterar en lösning utvecklad av Beckhoff Automation. Det visar sig att detta är en relativt sett dåligt utvecklad egenskap i EtherCAT. Den presenterade metoden medför till exempel att det tar nästan en hel sekund innan reserv-mastern tar över ifall det uppstår fel i den primära, dessutom är funktionen för synkronisering av klockorna i slav-enheterna inte tillgänglig när den här metoden används. Studien presenterar även en idé om en annan möjlig lösning för att åstadkomma master-redundans i EtherCAT nätverk. Fördelen med den är att den skulle göra funktionen för att synkronisera klockorna i slav-enheterna möjlig även fast systemet innehåller master-redundans. Båda de presenterade lösningarna är mer koncept än funktioner färdiga att använda, detta gäller i synnerhet den andra lösningen, som ännu bara är i idéstadiet. Bristen på väl fungerande lösningar för master-redundans gör att EtherCAT system bör konstrueras så att korta stopp i kom­munikationen inte kan skada systemet i sig själv, intilliggande system eller människor som är i kontakt med systemet

Towards securing hard real-time networked embedded devices and systems : a cBPF implementation for an FPGA

In this body of work we describe preliminary work implementing a Berkely Packet Filter, in its original conception, in an FPGA. The purpose is packet filtering and ingress traffic shaping in security-relevant applications in distributed embedded nodes. We specifically target PROFINET nodes in hard real-time applications where network security is an open issue. We describe the motivation, implementation and verification including performance characteristics. We conclude that such a filter can be used to not only for protection against simple denial-of-service attacks but also for ingress protocol management and potentially for the implementation of system-wide security policies

Using the ethernet protocol for real-time communications in embedded systems

Doutoramento em Engenharia ElectrotécnicaOs Sistemas Computacionais de Controlo Distribuído (SCCD) estão muito disseminados em aplicações que vão desde o controlo de processos e manufactura a automóveis, aviões e robôs. Muitas aplicações são de natureza tempo-real, ou seja, impõem fortes restrições às propriedades subjacentes aos sistemas de controlo, gerando a necessidade de fornecer um comportamento temporal previsível durante períodos alargados de tempo. Em particular, dependendo da aplicação, uma falha em garantir as restrições pode causar importantes perdas económicas ou mesmo pôr vidas humanas em risco. Actualmente, a quantidade e funcionalidade dos modernos SCCD têm crescido firmemente. Esta evolução é motivada por uma nova classe de aplicações que requer maior demanda de recursos tais como aplicações de multimedia (por exemplo visão), bem como pela tendência em usar grande número de processadres simples e interconectados, em vez de poucos e poderosos processadores, encapsulando cada funcionalidade num único processador. Consequentemente, a quantidade de informação que deve ser trocada entre os nós da rede também cresceu drasticamente nos últimos anos e está agora atingindo os limites que podem ser obtidos por tradicionais barramentos de campo, como por exempo CAN, WorldFIP, PROFIBUS. Outras alternativas são pois requeridas para suportar a necessidade de largura de banda e a manutenção de exigências dos sistemas de comunicação tempo-real: previsibilidade, pontualidade, atraso e variação de período limitados. Uma das linhas de trabalho tem apostado na Ethernet, tirando vantagem dos baixos custos dos circuitos, da elevada largura de banda, da fácil integração com a Internet, e da simplicidade em promover expansões e compatibilidade com redes usadas na estrutura administrativa das empresas industriais. Porém, o mecanismo padronizado de acesso ao meio da Ethernet (CSMA/CD) é destrutivo e não determinístico, o que impede seu uso directo ao nível de campo ou pelo menos em aplicações de comunicação tempo-real. Apesar disso, muitas abordagens diferentes têm sido propostas e usadas para obter comportamento tempo-real em Ethernet. As abordagens actuais para dotar de comportamento tempo-real Ethernet partilhada apresentam desvantagens tais como: exigência de hardware especializado, fornecimento de garantias temporais estatísticas, ineficiência na utilização da largura de banda ou na reposta tempo-real. São ainda por vezes inflexíveis com respeito às propriedades de tráfego bem como com as políticas de escalonamento. Podem exigir processadores com elevado poder de cálculo. Finalmente não permitem que estações tempo-real possam coexistir com estações Ethernet standard no mesmo segmento. Uma proposta recente, o algoritmo hBEB, permite a coexistência de estações tempo-real e standard no mesmo segmento. Contudo, apenas uma estação tempo-real pode estar activa, o que é inaceitável para aplicações de automação e controlo. Esta tese discute uma nova solução para promover tempo-real em Ethernet partilhada, baseando-se na passagem implícita de testemunho de forma similar à usada pelo protocolo P-NET. Esta técnica é um mecanismo de acesso ao meio físico pouco exigente em termos de processamento, sendo portanto adequada para implementar uma rede de dispositivos baseados em processadores de baixo poder de cálculo e controladores Ethernet standard. Esta tese apresenta ainda uma proposta de implementação do VTPE em IP core para superar algumas dificuldades derivadas de funcionalidades que não são suportadas por controladores standard, nomeadamente a arbitragem do meio físico durante a transmissão de uma trama. Esta nova proposta pode aumentar muito a eficiência do VTPE no uso da largura de banda. O VTPE, assim como P-NET ou protocolos similares, permite a uma estação apenas comunicar uma vez por cada circulação do testemunho. Esta imposição pode causar bloqueios de comunicação por períodos inaceitáveis em aplicações com tráfego isócrono, por exemplo multimedia. Uma solução proposta permite que uma estação possa aceder ao meio físico mais de uma vez por cada circulação do token. Os resultados experimentais a as análises desenvolvidas mostram que o bloqueio pode ser drasticamente reduzido. Por último esta tese discute uma variante do protocolo VTPE, o VTPE/h- BEB, que permite que mais de uma estação hBEB possa coexistir com diversas estações Ethernet standard num mesmo segmento partilhado. Um demonstrador para prova de conceito bem como uma aplicação foram também implementados.Distributed Computer-Control Systems (DCCS) are widely disseminated in applications ranging from automation and control to automotive, avionics and robotics. Many of these applications are real-time, posing stringent constraints to the properties of underlying control systems, which arise from the need to provide predictable behaviour during extended time periods. Depending on the particular type of application, a failure to meet these constraints can cause important economic losses or can even put human life in risk. Currently the number and functionality of modern DCCSs have been increasing steadily. This evolution has been motivated for a new class of applications of more resource demanding applications, such as multimedia (e.g. machine vision), as well as by the trend to use large numbers of simple interconnected processors, instead of a few powerful ones, encapsulating each functionality in one single processor. Consequently, the amount of information that must be exchanged among the network nodes has also increased dramatically and is now reaching the limits achievable by traditional fieldbuses. Therefore, other alternatives are required to support higher bandwidth demands while keeping the main requirements of a real-time communication system: predictability, timeliness, bounded delays and jitter. Efforts have been made with Ethernet to take advantage of the low cost of the silicon, high bandwidth, easy integration with the Internet, easy expansion and compatibility with the networks used at higher layers in the factory structure. However its standardized media access control (CSMA/CD) is destructive and not deterministic, impairing its direct use at field level at least for real-time communication. Despite this, many solutions have been proposed to achieve real-time behavior in Ethernet. However they present several disadvantages: requiring specialized hardware, providing statistical timeliness guarantees only, being bandwidth or response-time inefficient, being inflexible concerning traffic properties and/or scheduling policy, or finally not allowing real-time stations to coexist with standard Ethernet stations in the same segment. A recent proposal, the hBEB algorithm, allows the coexistence of real-time and standard Ethernet stations in the same shared segment. However hBEB limits at most one real-time station per segment which is unacceptable for applications in industrial automation and process control. This thesis discusses a new real-time shared Ethernet solution based on the virtual token passing technique similarly to the one used by the P-NET protocol. This technique is a medium access control mechanism that requires small processing power, being suitable to implement devices based on processors with small processing power. The solution is called Virtual Token Passing Ethernet or VTPE. This proposal discusses the modifications required in the Ethernet frame format, the temporal analysis to guarantee real-time communication and the implementation of two demonstrators based on microcontrollers and standard Ethernet controllers. This thesis also presents a proposal to implement VTPE in an IP Core to overcome some difficulties derived from limitations of standard Ethernet controllers, namely to allow medium access control during a frame transmission. This proposal can increase the bandwidth efficiency of VTPE. VTPE, as well as P-NET or any other protocol based on circular token rotation technique, only allows a station to communicate once for each token round. This design imposition can cause unacceptable communication blocking in applications with isochronous traffic such as multimedia. An improvement in the VTPE proposal enables a station to access the medium more than once per token round. The experimental results as well as the temporal analysis show that the blocking can be drastically reduced. This improvement can also be used in the P-NET protocol. Finally this thesis proposes a variant of VTPE, named VTPE/hBEB, to be implemented in Ethernet controllers that are able to support the hBEB algorithm. The VTPE/hBEB allows more than one hBEB station to coexist with several standard Ethernet stations in the same shared Ethernet segment. A demonstrator for the VTPE/hBEB validation, as well as an application, are also presented and discussed

Flexible management of bandwidth and redundancy in fieldbuses

Doutoramento em Engenharia ElectrotécnicaOs sistemas distribuídos embarcados (Distributed Embedded Systems – DES) têm sido usados ao longo dos últimos anos em muitos domínios de aplicação, da robótica, ao controlo de processos industriais passando pela aviónica e pelas aplicações veiculares, esperando-se que esta tendência continue nos próximos anos. A confiança no funcionamento é uma propriedade importante nestes domínios de aplicação, visto que os serviços têm de ser executados em tempo útil e de forma previsível, caso contrário, podem ocorrer danos económicos ou a vida de seres humanos poderá ser posta em causa. Na fase de projecto destes sistemas é impossível prever todos os cenários de falhas devido ao não determinismo do ambiente envolvente, sendo necessária a inclusão de mecanismos de tolerância a falhas. Adicionalmente, algumas destas aplicações requerem muita largura de banda, que também poderá ser usada para a evolução dos sistemas, adicionandolhes novas funcionalidades. A flexibilidade de um sistema é uma propriedade importante, pois permite a sua adaptação às condições e requisitos envolventes, contribuindo também para a simplicidade de manutenção e reparação. Adicionalmente, nos sistemas embarcados, a flexibilidade também é importante por potenciar uma melhor utilização dos, muitas vezes escassos, recursos existentes. Uma forma evidente de aumentar a largura de banda e a tolerância a falhas dos sistemas embarcados distribuídos é a replicação dos barramentos do sistema. Algumas soluções existentes, quer comerciais quer académicas, propõem a replicação dos barramentos para aumento da largura de banda ou para aumento da tolerância a falhas. No entanto e quase invariavelmente, o propósito é apenas um, sendo raras as soluções que disponibilizam uma maior largura de banda e um aumento da tolerância a falhas. Um destes raros exemplos é o FlexRay, com a limitação de apenas ser permitido o uso de dois barramentos. Esta tese apresentada e discute uma proposta para usar a replicação de barramentos de uma forma flexível com o objectivo duplo de aumentar a largura de banda e a tolerância a falhas. A flexibilidade dos protocolos propostos também permite a gestão dinâmica da topologia da rede, sendo o número de barramentos apenas limitado pelo hardware/software. As propostas desta tese foram validadas recorrendo ao barramento de campo CAN – Controller Area Network, escolhido devido à sua grande implantação no mercado. Mais especificamente, as soluções propostas foram implementadas e validadas usando um paradigma que combina flexibilidade com comunicações event-triggered e time-triggered: o FTT – Flexible Time- Triggered. No entanto, uma generalização para CAN nativo é também apresentada e discutida. A inclusão de mecanismos de replicação do barramento impõe a alteração dos antigos protocolos de replicação e substituição do nó mestre, bem como a definição de novos protocolos para esta finalidade. Este trabalho tira partido da arquitectura centralizada e da replicação do nó mestre para suportar de forma eficiente e flexível a replicação de barramentos. Em caso de ocorrência de uma falta num barramento (ou barramentos) que poderia provocar uma falha no sistema, os protocolos e componentes propostos nesta tese fazem com que o sistema reaja, mudando para um modo de funcionamento degradado. As mensagens que estavam a ser transmitidas nos barramentos onde ocorreu a falta são reencaminhadas para os outros barramentos. A replicação do nó mestre baseia-se numa estratégia líder-seguidores (leaderfollowers), onde o líder (leader) controla todo o sistema enquanto os seguidores (followers) servem como nós de reserva. Se um erro ocorrer no nó líder, um dos nós seguidores passará a controlar o sistema de uma forma transparente e mantendo as mesmas funcionalidades. As propostas desta tese foram também generalizadas para CAN nativo, tendo sido para tal propostos dois componentes adicionais. É, desta forma possível ter as mesmas capacidades de tolerância a falhas ao nível dos barramentos juntamente com a gestão dinâmica da topologia de rede. Todas as propostas desta tese foram implementadas e avaliadas. Uma implementação inicial, apenas com um barramento foi avaliada recorrendo a uma aplicação real, uma equipa de futebol robótico onde o protocolo FTT-CAN foi usado no controlo de movimento e da odometria. A avaliação do sistema com múltiplos barramentos foi feita numa plataforma de teste em laboratório. Para tal foi desenvolvido um sistema de injecção de faltas que permite impor faltas nos barramentos e nos nós mestre, e um sistema de medida de atrasos destinado a medir o tempo de resposta após a ocorrência de uma falta.Distributed embedded systems (DES) have been widely used in the last few decades in several application domains, from robotics, industrial process control, avionics and automotive. In fact, it is expectable that this trend will continue in the next years. In some of these application fields the dependability requirements are very important since the fail to provide services in a timely and predictable manner may cause important economic losses or even put humans in risk. In the design phase it is impossible to predict all the possible scenarios of faults, due to the non deterministic behaviour of the surrounding environment. In that way, the fault tolerance mechanisms must be included in the distributed embedded system to prevent failures occurrence. Also, many application domains require a high available bandwidth to perform the desired functions, or to turn possible the scaling with the addition of new features. The flexibility of a system also plays an important role, since it improves the capability to adapt to the surrounding world, and to the simplicity of the repair and maintenance. The flexibility improves the efficiency of all the system by providing a way to efficiently manage the available resources. This is very important in embedded systems due to the limited resources often available. A natural way to improve the bandwidth and the fault tolerance in distributed systems is to use replicated buses. Commercial and academic solutions propose the use of replicated fieldbuses for a single purpose only, either to improve the fault tolerance or to improve the available bandwidth, being the first the most common. One illustrative exception is FlexRay where the bus replica can be used to improve the bandwidth of the overall system, besides enabling redundant communications. However, only one bus replica can be used. In this thesis, a flexible bus replication scheme to improve both the dependability and the throughput of fieldbuses is presented and studied. It can be applied to any number of replicated buses, provided the required hardware support is available. The flexible use of the replicated buses can achieve an also flexible management of the network topology. This claim has been validated using the Controller Area Network (CAN) fieldbus, which has been chosen because it is widely spread in millions of systems. In fact, the proposed solution uses a paradigm that combines flexibility, time and event triggered communication, that is the Flexible Time- Triggered over CAN network (FTT-CAN). However, a generalization to native CAN is also presented and studied. The inclusion of bus replication in FTT-CAN imposes not only new mechanisms but also changes of the mechanisms associated with the master replication, which has been already studied in previous research work. In this work, these mechanisms were combined and take advantage of the centralized architecture and of the redundant masters to support an efficient and flexible bus replication. When considering the system operation, if a fault in the bus (or buses) occurs, and the consequent error leads to a system failure, the system reacts, switching to a degraded mode, where the message flows that were transmitted in the faulty bus (or buses) change to the non-faulty ones. The central node replication uses a leader-follower strategy, where the leader controls the system while the followers serve as backups. If an error occurs in the leader, a backup will take the system control maintaining the system with the same functionalities. The system has been generalized for native CAN, using two additional components that provide the same fault tolerance capabilities at the bus level, and also enable the dynamic management of the network topology. All the referred proposals were implemented and assessed in the scope of this work. The single bus version of FTT-CAN was assessed using a real application, a robotic soccer team, which has obtained excellent results in international competitions. There, the FTT-CAN based embedded system has been applied in the low level control, where, mainly it is responsible for the motion control and odometry. For the case of the multiple buses system, the assessment was performed in a laboratory test bed. For this, a fault injector was developed in order to impose faults in the buses and in the central nodes. To measure the time reaction of the system, a special hardware has been developed: a delay measurement system. It is able to measure delays between two important time marks for posterior offline analysis of the obtained values

The Virtual Bus: A Network Architecture Designed to Support Modular-Redundant Distributed Periodic Real-Time Control Systems

The Virtual Bus network architecture uses physical layer switching and a combination of space- and time-division multiplexing to link segments of a partial mesh network together on schedule to temporarily form contention-free multi-hop, multi-drop simplex signalling paths, or 'virtual buses'. Network resources are scheduled and routed by a dynamic distributed resource allocation mechanism with self-forming and self-healing characteristics. Multiple virtual buses can coexist simultaneously in a single network, as the resources allocated to each bus are orthogonal in either space or time. The Virtual Bus architecture achieves deterministic delivery times for time-sensitive traffic over multi-hop partial mesh networks by employing true line-speed switching; delays of around 15ns at each switching point are demonstrated experimentally, and further reductions in switching delays are shown to be achievable. Virtual buses are inherently multicast, with delivery skew across multiple destinations proportional to the difference in equivalent physical length to each destination. The Virtual Bus architecture is not a purely theoretical concept; a small research platform has been constructed for development, testing and demonstration purposes