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Evaluating program flow analysis for WCET calculations at Volvo CE
Mälardalen University, Department of Computer Science and Electronics.
2007 (English)Report (Other academic)
Abstract [en]

A prerequisite for creating a safe and predictable real time computer system is to have knowledge about its

timing behavior during operation. The Worst Case Execution Time (WCET) is one of the key values to

consider when predicting this timing behavior, since it ensures that every task meets its deadline in the

system. A missed deadline in systems with critical tasks can lead to severe consequences.

Dynamic WCET analysis is a widely used method to derive WCET value in the industry today. The

method is based on using simulation and measurement techniques. The WCET value is derived by

performing a set of automatic tests on the system and measure its execution time. To ensure that a safe

WCET value is derived the automatic tests must cover the worst case scenario, which is tough to find when

the systems increase in size and complexity.

Static WCET analysis is an alternative method, where it is guaranteed that an overestimated WCET value is

obtained. The method uses mathematical models of the system hard and software to calculate WCET.

Therefore, this method has been the main research subject for many research groups. One of the key

components in making a safe and tight WCET value, using static WCET analysis technique, is program

flow information.

The information describes the possible program flows through the program; this information can be either

provided to the WCET analyzer manually, by user, or automatically, by a flow analyzer. Deriving flow

information manually is done by:

• Studying and analyzing the program source code, and manually calculating loop bounds,

detecting infeasible paths and making recursion bounds.

• Providing the information to a WCET analyzer, usually by writing them in form of

annotations in a program language supported by the analyzer.

The steps above are time consuming and unsafe when the program complexity increases, that makes it

preferable to use flow analysis to provide flow information. This has been shown in a previous study at

Volvo Construction Equipment, where the WCET analysis tool aiT has been used. This work will complete

the study by evaluating an automatic method, using flow analyzers to derive flow information for the

analyzed code.

Flow analyzers use mathematical methods to model and derive flow information of program source code.

This flow information makes deriving WCET estimates safe, simple and requires no or minimum user

interaction. Therefore, Volvo CE is interested in the development of static WCET analysis tools where the

flow information is obtained automatically.

This work evaluated SWEdish Execution time Tool (SWEET), a prototype WCET analysis tool built by a

research group from Malardalens University (MDH). The results are compared to the ones obtained in

previous work using aiT, where the flow information is derived manually.

We have found that SWEET derived the same flow information that was derived manually, but since it is a

prototype tool a lot of manual work was needed. The manual work consisted mainly of adapting the Volvo

CE application to the SWEET analysis environment. This work has also contributed in development of

SWEET, adding new functionality and making it more users friendly.

Place, publisher, year, edition, pages
2007.
Identifiers
URN: urn:nbn:se:mdh:diva-7062OAI: oai:DiVA.org:mdh-7062DiVA, id: diva2:237072
Note

This report is a MSc thesis performed at the Department of Electronic, Computer, and Software Systems (ECS) at KTH, but was supervised by Jan Gustafsson, IDE, for the WCET project.

Available from: 2009-09-25 Created: 2009-09-25 Last updated: 2015-07-30Bibliographically approved

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