| 1. |
- Altenbernd, Peter, et al.
(författare)
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Automatic Generation of Timing Models for Timing Analysis of High-Level Code
- 2011
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Ingår i: 19th International Conference on Real-Time and Network Systems (RTNS2011).
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Konferensbidrag (refereegranskat)abstract
- Traditional timing analysis is applied only in the late stages of embedded system software development, when the hardware is available and the code is compiled and linked. However, preliminary timing estimates are often needed already in early stages of system development, both for hard and soft real-time systems. If the hardware is not yet fully accessible, or the code is not yet ready to compile or link, then the timing estimation must be done for the source code rather than for the binary. This paper describes how source-level timing models can be derived automatically for given combinations of hardware architecture and compiler. The models are identified from measured execution times for a set of synthetic "training programs" compiled for the hardware platform in question. The models can be used to derive source-level WCET estimates, as well as for estimating the execution times for single program runs. Our experiments indicate that the models can predict the execution times of the final, compiled code with a deviation up to 20%.
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| 2. |
- Altenbernd, Peter, et al.
(författare)
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Early execution time-estimation through automatically generated timing models
- 2016
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Ingår i: Real-time systems. - : Springer Science and Business Media LLC. - 0922-6443 .- 1573-1383. ; 52:6, s. 731-760
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Tidskriftsartikel (refereegranskat)abstract
- Traditional timing analysis, such as worst-case execution time analysis, is normally applied only in the late stages of embedded system software development, when the hardware is available and the code is compiled and linked. However, preliminary timing estimates are often needed in early stages of system development as an essential prerequisite for the configuration of the hardware setup and dimensioning of the system. During this phase the hardware is often not available, and the code might not be ready to link. This article describes an approach to predict the execution time of software through an early, source-level timing analysis. A timing model for source code is automatically derived from a given combination of hardware architecture and compiler. The model is identified from measured execution times for a set of synthetic training programs, compiled for the hardware platform in question. It can be used to estimate the execution time for code running on the platform: the estimation is then done directly from the source code, without compiling and running it. Our experiments show that, using this model, we can predict the execution times of the final, compiled code surprisingly well. For instance, we achieve an average deviation of 8 % for a set of benchmark programs for the ARM7 architecture.
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| 3. |
- Barkah, Dani, et al.
(författare)
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Evaluation of Automatic Flow Analysis for WCET Calculation on Industrial Real-Time System Code
- 2008
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Ingår i: Proceedings - Euromicro Conference on Real-Time Systems, 2008. - 9780769532981 ; , s. 331-340
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Konferensbidrag (refereegranskat)abstract
- A static Worst-Case Execution Time (WCET) analysis derives upper bounds for the execution times of programs. Such analysts requires information about the possible program flows. The current practice is to provide this information manually, which can be laborious and error-prone. An alternative is to derive this information through an automated flow analysis. In this article, we present a case study where an automatic flowanalysis method was tested on industrial real-time system code. The same code was the subject of an earlier WCET case study, where it was analysed using manual annotations for the flow information. The purpose of the current study was to see to which extent the same flow information could be found automatically. The results show that for the most part this is indeed possible, and we could derive comparable WCET estimates using the automatically generated flow information. In addition, valuable insights were gained on what is needed to make flow analysis methods work on real production code.
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| 4. |
- Bastholm Rahmner, Pia, et al.
(författare)
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Variations in understanding the drug-prescribing process : a qualitative study among Swedish GPs
- 2009
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Ingår i: Family Practice. - : Oxford University Press (OUP). - 0263-2136 .- 1460-2229. ; 26:2, s. 121-127
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: A majority of doctor-patient meetings result in the patient getting a prescription. This underlines the need for a high-quality prescription process. While studies have been made on single therapeutic drug groups, a complete study of the physicians' general thought process that comprises the prescription of all drugs still remains to be made. OBJECTIVE: To identify variations in ways of understanding drug prescribing among GPs. METHODS: A descriptive qualitative study was conducted with 20 Swedish physicians. Informants were recruited purposively and their understandings about prescribing were studied in semi-structured interviews. Data were analysed using a phenomenographic approach. RESULTS: Five categories were identified as follows: (A) GP prescribed safe, reliable and well-documented drugs for obvious complaints; (B) GP sought to convince the patient of the most effective drug treatment; (C) GP chose the best drug treatment taking into consideration the patient's entire life situation; (D) GP used clinical judgement and close follow-up to minimize unnecessary drug prescribing and (E) GP prescribed drugs which are cheap for society and environmentally friendly. The categories are interrelated, but have different foci: the biomedical, the patient and the society. Each GP had more than one view but none included all five. The findings also indicate that complexity increases when a drug is prescribed for primary or secondary prevention. CONCLUSIONS: GPs understand prescribing differently despite similar external circumstances. The most significant factor to influence prescribing behaviour was the physician's patient relation approach. GPs may need to reflect on difficulties they face while prescribing to enhance their understandings.
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| 5. |
- Bygde, Stefan, 1980-
(författare)
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Static WCET Analysis Based on Abstract Interpretation and Counting of Elements
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In a real-time system, it is crucial to ensure that all tasks of the system holdtheir deadlines. A missed deadline in a real-time system means that the systemhas not been able to function correctly. If the system is safety critical, this canlead to disaster. To ensure that all tasks keep their deadlines, the Worst-CaseExecution Time (WCET) of these tasks has to be known. This can be done bymeasuring the execution times of a task, however, this is inflexible, time consumingand in general not safe (i.e., the worst-casemight not be found). Unlessthe task is measured with all possible input combinations and configurations,which is in most cases out of the question, there is no way to guarantee that thelongest measured time actually corresponds to the real worst case.Static analysis analyses a safe model of the hardware together with thesource or object code of a program to derive an estimate of theWCET. This estimateis guaranteed to be equal to or greater than the real WCET. This is doneby making calculations which in all steps make sure that the time is exactlyor conservatively estimated. In many cases, however, the execution time of atask or a program is highly dependent on the given input. Thus, the estimatedworst case may correspond to some input or configuration which is rarely (ornever) used in practice. For such systems, where execution time is highly inputdependent, a more accurate timing analysis which take input into considerationis desired.In this thesis we present a framework based on abstract interpretation andcounting of possible semantic states of a program. This is a general methodof WCET analysis, which is language independent and platform independent.The two main applications of this framework are a loop bound analysis and aparametric analysis. The loop bound analysis can be used to quickly find upperbounds for loops in a program while the parametric framework provides aninput-dependent estimation of theWCET. The input-dependent estimation cangive much more accurate estimates if the input is known at run-time.
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| 6. |
- Dodig-Crnkovic, Gordana, 1955-
(författare)
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Investigations into Information Semantics and Ethics of Computing
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The recent development of the research field of Computing and Philosophy has triggered investigations into the theoretical foundations of computing and information.This thesis consists of two parts which are the result of studies in two areas of Philosophy of Computing (PC) and Philosophy of Information (PI) regarding the production of meaning (semantics) and the value system with applications (ethics).The first part develops a unified dual-aspect theory of information and computation, in which information is characterized as structure, and computation is the information dynamics. This enables naturalization of epistemology, based on interactive information representation and communication. In the study of systems modeling, meaning, truth and agency are discussed within the framework of the PI/PC unification.The second part of the thesis addresses the necessity of ethical judgment in rational agency illustrated by the problem of information privacy and surveillance in the networked society. The value grounds and socio-technological solutions for securing trustworthiness of computing are analyzed. Privacy issues clearly show the need for computing professionals to contribute to understanding of the technological mechanisms of Information and Communication Technology.The main original contribution of this thesis is the unified dual-aspect theory of computation/information. Semantics of information is seen as a part of the data-information-knowledge structuring, in which complex structures are self-organized by the computational processing of information. Within the unified model, complexity is a result of computational processes on informational structures. The thesis argues for the necessity of computing beyond the Turing-Church limit, motivated by natural computation, and wider by pancomputationalism and paninformationalism, seen as two complementary views of the same physical reality. Moreover, it follows that pancomputationalism does not depend on the assumption that the physical world on some basic level is digital. Contrary to many believes it is entirely compatible with dual (analogue/digital) quantum-mechanical computing.
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| 7. |
- Ermedahl, Andreas, et al.
(författare)
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Deriving the Worst-Case Execution Time Input Values
- 2009
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Ingår i: 21st Euromicro Conference of Real-Time Systems, (ECRTS'09). - Dublin, Ireland. - 9780769537245 ; , s. 45-54
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Konferensbidrag (refereegranskat)abstract
- A Worst-Case Execution Time (WCET) analysis derives upper bounds for execution times of programs. Such bounds are crucial when designing and verifying real-time systems. A major problem with today's WCET analysis approaches is that there is no feedback on the particular values of the input variables that cause the program's WCET. However, this is important information for the real-time system developer. We present a novel approach to overcome this problem. In particular, we present a method, based on a combination of input-sensitive static WCET analysis and systematic search over the value space of the input variables, to derive the input value combination that causes the WCET. We also present several different approaches to speed up the search. Our evaluations show that the WCET input values can be relatively quickly derived for many type of programs, even for program with large input value spaces. We also show that the WCET estimates derived using the WCET input values often are much tighter than the WCET estimates derived when all possible input value combinations are taken into account.
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| 8. |
- Ermedahl, Andreas, et al.
(författare)
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Deriving WCET Bounds by Abstract Execution
- 2011
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Ingår i: Proc. 11th International Workshop on Worst-Case Execution Time (WCET) Analysis (WCET 2011:). - 9781632663153 ; , s. 72-82
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Konferensbidrag (refereegranskat)abstract
- Standard static WCET analysis methods today are based on the IPET technique, where WCET estimation is formulated as an integer linear programming (ILP) problem subject to linear program flow constraints with an objective function derived from the hardware timing model. The estimate is then calculated by an ILP solver. The hardware cost model, as well as the program flow constraints, are often derived using a static program analysis framework such as abstract interpretation. An alternative idea to estimate the WCET is to add time as an explicit variable, incremented for each basic block in the code. The possible values of this variable can then be bound by a value analysis. We have implemented this idea by integrating the time estimation in our Abstract Execution method for calculating program flow constraints. This method is in principle a very detailed value analysis. As it computes intervals bounding variable values, it bounds both the BCET and the WCET. In addition, it derives the explicit execution paths through the program which correspond to the calculated BCET and WCET bounds. We have compared the precision and the analysis time with the traditional IPET technique for a number of benchmark programs, and show that the new method typically is capable of calculating as tight or even tighter WCET estimates in shorter time. Our current implementation can handle simple timing models with constant execution times for basic blocks and edges in the CFG, but it is straightforward to extend the method to more detailed hardware timing models.
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| 9. |
- Ermedahl, Andreas, et al.
(författare)
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Loop Bound Analysis based on a Combination of Program Slicing, Abstract Interpretation, and Invariant Analysis
- 2007
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Ingår i: OpenAccess Series in Informatics, Volume 6, 2007. - 9783939897057
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Konferensbidrag (refereegranskat)abstract
- Static Worst-Case Execution Time (WCET) analysis is a technique to derive upper bounds for the execution times of programs. Such bounds are crucial when designing and verifying real-time systems. A key component for static derivation of precise WCET estimates is upper bounds on the number of times different loops can be iterated. In this paper we present an approach for deriving upper loop bounds based on a combination of standard program analysis techniques. The idea is to bound the number of different states in the loop which can influence the exit conditions. Given that the loop terminates, this number provides an upper loop bound. An algorithm based on the approach has been implemented in our WCET analysis tool SWEET. We evaluate the algorithm on a number of standard WCET benchmarks, giving evidence that it is capable to derive valid bounds for many types of loops.
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| 10. |
- Gustafsson, Jan, et al.
(författare)
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ALF - A Language for WCET Flow Analysis
- 2009
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Ingår i: OpenAccess Series in Informatics Volume 10, 2009. - 9783939897149
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Konferensbidrag (refereegranskat)abstract
- Static Worst-Case Execution Time (WCET) analysis derives upper bounds for the execution times of programs. Such bounds are crucial when designing and verifying real-time systems. A key component in static WCET analysis is the flow analysis, which derives bounds on the number of times different code entities can be executed. Examples of flow information derived by a flow analysis are loop bounds and infeasible paths. Flow analysis can be performed on source code, intermediate code, or binary code: for the latter, there is a proliferation of instruction sets. Thus, flow analysis must deal with many code formats. However, the basic flow analysis techniques are more or less the same regardless of the code format. Thus, an interesting option is to define a common code format for flow analysis, which also allows for easy translation from the other formats. Flow analyses for this common format will then be portable, in principle supporting all types of code formats which can be translated to this format. Further, a common format simplifies the development of flow analyses, since only one specific code format needs to be targeted. This paper presents such a common code format, the ALF language (ARTIST2 Language for WCET Flow Analysis).
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