232 research outputs found
Setting target rotation time in PROFIBUS based real-time distributed applications
In this paper, we analyse the ability of Profibus fieldbus to cope with
the real-time requirements of a Distributed Computer Control System (DCCS),
where messages associated to discrete events must be made available within a
maximum bound time. Our methodology is based on the knowledge of real-time
traffic characteristics, setting the network parameters in order to cope with
timing requirements. Since non-real-time traffic characteristics are usually
unknown at the design stage, we consider an operational profile where,
constraining non-real-time traffic at the application level, we assure that realtime
requirements are met.FLAD; ISE
Engineering real-time applications with WorldFIP: tools and analysis
WorldFIP is standardised as European Norm EN 50170 - General Purpose
Field Communication System. Field communication systems (fieldbuses) started to be
widely used as the communication support for distributed computer-controlled systems
(DCCS), and are being used in all sorts of process control and manufacturing
applications within different types of industries. There are several advantages in using
fieldbuses as a replacement of for the traditional point-to-point links between
sensors/actuators and computer-based control systems. Indeed they concern economical
ones (cable savings) but, importantly, fieldbuses allow an increased decentralisation
and distribution of the processing power over the field. Typically DCCS have real-time
requirements that must be fulfilled. By this, we mean that process data must be
transferred between network computing nodes within a maximum admissible time span.
WorldFIP has very interesting mechanisms to schedule data transfers. It explicit
distinguishes to types of traffic: periodic and aperiodic. In this paper we describe how
WorldFIP handles these two types of traffic, and more importantly, we provide a
comprehensive analysis for guaranteeing the real-time requirements of both types of
traffic. A major contribution is made in the analysis of worst-case response time of
aperiodic transfer requests
The DEAR-COTS hard real-time subsystem
In this report, the Hard Real-Time Subsystem of DEAR-COTS is described, and the services
it must provide are identified. This report is an input of ISEP/IPP and FEUP for the
specification of the DEAR-COTS architecture (deliverable to the FCT)
To Ada or not To Ada: Adaing vs. Javaing in real-time systems
Ada is really an unfortunate Lady. After years fighting against C/C++ villains, her major lift-up
(Ada 95) had brought up a promise of fortune. However, a new strong villain (Java) has appeared
trying to end her struggle for survival.
Ada has now to fight with her own weapons. She will only prosper by her own merits. But two
questions emerge. Do they exist? Are they better than Java’s? Our opinion is that they do exist,
and are not matched by any other programming languageFLAD; DEMEGI/FEU
The virtual token-passing Ethernet implementation and experimental results
This paper presents the design and first experimental results of VTPE (Virtual Token-passing Ethernet). VTPE \nis a deterministic protocol for real-time applications based on shared Ethernet, aimed to be used either in small \nprocessing power processors or in powerful ones. It is based on implicit token rotation similar to the virtual \ntoken-passing used in the P-NET protocol. The VTPE implementation leads to reduced program code, thus \nfitting in small microcontrollers' memory and imposing low communication overhead. \
Ethernet goes real-time: a survey on research and technological developments
Ethernet is the most popular LAN technology. Its low price and robustness, resulting from its
wide acceptance and deployment, has created an eagerness to expand its responsibilities to
the factory-floor, where real-time requirements are to be fulfilled. However, it is difficult to
build a real-time control network using Ethernet, because its MAC protocol, the 1-persistent
CSMA/CD protocol with the BEB collision resolution algorithm, has unpredictable delay
characteristics. Many anticipate that the recent technological advances in Ethernet such as
the emerging Fast/Gigabit Ethernet, micro-segmentation and full-duplex operation using
switches will also enable it to support time-critical applications. This technical report provides
a comprehensive look at the unpredictability inherent to Ethernet and at recent technological
advances towards real-time operation
On the adaptation of broadcast transactions in token-passing fieldbus networks with heterogeneous transmission media
Broadcast networks that are characterised by having
different physical layers (PhL) demand some kind of
traffic adaptation between segments, in order to
avoid traffic congestion in linking devices. In many
LANs, this problem is solved by the actual linking
devices, which use some kind of flow control
mechanism that either tell transmitting stations to
pause (the transmission) or just discard frames. In
this paper, we address the case of token-passing
fieldbus networks operating in a broadcast fashion
and involving message transactions over
heterogeneous (wired or wireless) physical layers.
For the addressed case, real-time and reliability
requirements demand a different solution to the
traffic adaptation problem. Our approach relies on
the insertion of an appropriate idle time before a
station issuing a request frame. In this way, we
guarantee that the linking devices’ queues do not
increase in a way that the timeliness properties of the
overall system turn out to be unsuitable for the
targeted applications
Supporting real-time distributed computer-controlled systems with multi-hop P-NET networks
Fieldbus communication networks aim to interconnect sensors, actuators and controllers within process control applications. Therefore, they constitute the foundation upon which real-time distributed computer-controlled systems can be implemented. P-NET is a fieldbus communication standard, which uses a virtual token-passing medium-access-control mechanism. In this paper pre-run-time schedulability conditions for supporting real-time traffic with P-NET networks are established. Essentially, formulae to evaluate the upper bound of the end-to-end communication delay in P-NET messages are provided. Using this upper bound, a feasibility test is then provided to check the timing requirements for accessing remote process variables. This paper also shows how P-NET network segmentation can significantly reduce the end-to-end communication delays for messages with stringent timing requirements
Formal verification of a group membership protocol using model checking
The development of safety-critical embedded applications in domains such as automotive or avionics is an exceedingly challenging intellectual task. This task can, however, be significantly simplified through the use of middleware that offers specialized fault-tolerant services. This middleware must provide a high assurance level that it operates correctly. In this paper, we present a formal verification of a protocol for one such service, a Group Membership Service, using model checking. Through this verification we discovered that although the protocol specification is correct, a previously proposed implementation is not
Industrial multimedia over factory-floor networks
In this paper we describe a real-time industrial communication network able to support both controlrelated
and multimedia traffic. The industrial communication network is based on the PROFIBUS
standard, with multimedia capabilities being provided by an adequate integration of TCP/IP protocols into
the PROFIBUS stack. From the operational point of view the integration of TCP/IP into PROFIBUS is by
itself a challenge, since the master-slave nature of the PROFIBUS MAC makes complex the
implementation of the symmetry inherent to IP communications. From the timeliness point of view the
challenge is two folded. On one hand the multimedia traffic should not interfere with the timing
requirements of the "native" control-related PROFIBUS traffic (typically hard real-time). On the other
hand multimedia traffic requires certain levels of quality-of-service to be attained. In this paper we
provide a methodology that enables fulfilling the timing requirements for both types of traffic in these
real-time industrial LAN. Moreover, we describe suitable algorithms for the scheduling support of
concurrent multimedia streams
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