| 1. |
- Redell, Ola
(författare)
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Analysis of tree-shaped transactions in distributed real time systems
- 2004
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Ingår i: 16TH EUROMICRO CONFERENCE ON REAL-TIME SYSTEMS, PROCEEDINGS. - 0769521762 ; , s. 239-248
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Konferensbidrag (refereegranskat)abstract
- A worst case response time analysis exploiting precedence constraints between fixed priority scheduled tasks in tree-shaped transactions is presented. The algorithm extends existing methods for analysis of linear transactions allowing a wider range of systems, in which tasks may trigger more than one succeeding task on their completion, i.e. the transactions form trees. It also improves existing methods, producing tighter response time bounds for tasks in both linear and tree-shaped transactions. The improvement is due to better exploitation of the precedence relations between tasks, which also makes the analysis faster than earlier. Simulation results show a significant reduction of estimated worst case response times when compared to earlier analysis methods for both linear and tree-shaped transactions. Such improvement leads to less pessimistic schedulability tests for distributed fixed priority scheduled systems.
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| 2. |
- Redell, Ola, et al.
(författare)
-
Calculating worst-case response times for static priority scheduled tasks with offsets and jitter
- 2002
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Ingår i: Proc 8th Real-time and embedded technology and applications symposium.
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Konferensbidrag (refereegranskat)abstract
- A method to perform exact worst case response time analysis for fixed priority tasks with offsets and release jitter is described. Available methods are either pessimistic or inefficient as they incorporate numerous time consuming schedule simulations in order to find the exact response times of tasks. The method presented here is based on the creation of the worst case conditions for the execution of each individual task instance within a hyperperiod. The worst case is built by choosing release jitter of higher priority tasks appropriately. Given these conditions, the corresponding task instance response time is calculated using partly iterative algorithms. Experiments comparing the efficiency of the proposed method to an alternative exact method based on schedule simulation show that the new method outperforms the latter. The analysis is expected to be particularly useful when analysing response times and schedulability of tasks that form transactions in distributed systems.
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| 3. |
- Redell, Ola, 1970-
(författare)
-
Response time analysis for implementation of distributed control systems
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Methods for performing response time analysis of real-timesystems are important, not only for their use in traditionalschedulability testing, but also for deriving bounds on outputtiming variations in control applications. Automatic controlsystems are inherently sensitive to variations in periodicityand end-to-end delays. Therefore, real-time performance needsto be considered during control design. For this purpose, anyreal-time analysis of a potential control implementation shouldproduce results that can easily be used to examine how theimplementation affects control performance. To find the maximumresponse time variation for a task, bounds on both minimum andmaximum response times are needed. A tight bound on thismaximum variation is useful in the analysis of controlperformance and can also be used to improve the results of someiterative response time analysis methods. In this thesis, threemethods for response time analysis are developed.While earlier research has focused on bounding maximumresponse times, one of the analysis methods in this thesisallows a computation of the minimum response times ofindependent fixed priority scheduled tasks. The analysis findsthe largest lower bound of response times for such tasks, whichleads to a tighter bound on the response time variations. Asecond analysis method allows exact computation of maximumresponse times for tasks whose arrival times are related byoffsets. The method is a complement to schedule simulationbased analysis, which it outperforms for systems with tasksthat may experience release jitter.A common design principle for distributed real-time systemsis to let the completion of one task trigger the start of oneor more successors. A third method supporting the analysis oftasks in such systems is described. The method extends andimproves earlier methods as it allows a generalized systemmodel and also results in tighter bounds than the originalmethods. This method has been implemented as part of a toolsetthat enables an integrated approach to the design and analysisof control systems and their implementation as distributedreal-time systems. As part of the thesis, models for describingdistributed control systems have been developed. The toolset,which is based on these models, uses the derived response timebounds in a control system performance analysis based onsimulation. The use of the toolset is exemplified in a smallcase study.Keywords:real-time systems, scheduling, response time,fixed priority, control, jitter, offset, schedulabilityanalysis
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| 4. |
- Redell, Ola, et al.
(författare)
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The AIDA toolset for design and implementation analysis of distributed real-time control systems
- 2004
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Ingår i: Microprocessors and microsystems. - : Elsevier BV. - 0141-9331 .- 1872-9436. ; 28:4, s. 163-182
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Tidskriftsartikel (refereegranskat)abstract
- This article introduces a toolset that integrates the design and performance analysis of control systems with embedded real-time system design. The toolset enables specification and analysis of real-time implementations of control applications. Control system designs are imported to a real-time system-modelling domain in which the functionality is distributed on a target computer system. The control functionality is partitioned into operating system processes, inter-process communications are defined and the triggering of processes is specified. Once the real-time design is complete, the response times and release jitter of the processes and their contained functions can be analysed and the system information exported back to the control domain. This enables analysis of the resulting control performance with account taken to implementation effects such as delays and release jitter due to resource sharing and scheduling. The usage of the toolset is demonstrated on a dual leg controller for a walking robot. The case study shows how the toolset is used to describe a system, from the control system specification to the design of its implementation on a distributed network of processors. Different implementation solutions are suggested and evaluated based on simulated control system performance.
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| 5. |
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