This is the home page for the unofficial swedish network for WCET research and applications.
Swedish: Detta är den hemsidan för det inofficiella svenska nätverket för forskning och tillämpningar inom WCET-området (längsta exekveringstider för program).
The calculation of WCET is an essential part of the design and implementation of real-time systems. WCET, which stands for Worst Case Execution Time, is a fundamental part of scheduling theory, where it it is used as a safe estimate of c (the computation time). The WCET can also be used to evaluate different solutions and algorithms, to debug programs, to find bottlenecks, and to to assess hardware needs.
The task is to estimate the WCET for a program with as small error as possible. The estimation must be safe (= no underestimation) and tight (=small or no overestimation), because underestimation means risk for missed deadlines, and overestimation means risk for waste of resources.
Traditional approach 1: Run the program and make time measurements. Unsafe, as there normally are far too many program paths to run!
Traditional approach 2: Count clock cycles manually (using assembler code). Tedious and for modern hardware, in practice impossible!
Current approach: Analyse the program without actually running it, using static analysis.
The research is performed on two levels.
High-level analysis, studying WCET-affecting factors like the input data and the function of the program (as defined in the source code).
Low-level analysis, studying how the compiler generates executable code and the behaviour of the processor, memory, cache, pipeline and other hardware.
The Swedish WCET network
The aim of this network is to make communication and exchange between people working in the area easier. It can also be used as a general source of information in this field available for a wider group of interested people. It is supported by ARTES, a national Swedish strategic research initiative in Real-Time Systems.
The network started as a study group i Uppsala within the ASTEC-project. The members of the group came from Computer Systems, Uppsala, IAR in Uppsala and Mälardalen University in Västerås (see links below). The group produced a state-of-the-art report of the WCET field in 1996 (in swedish, see here).
Now the group grows to a national network. Are you interested to join? You can find the contact person for the network at the bottom of the page. There is a mailing list for the group, where interested people can join.
WCET Research Groups in Sweden
The Department of Computer Systems at Uppsala University: The Execution Time Analysis Group within ASTEC-RT, Jakob Engblom (industrial Ph.D.student), Andreas Ermedahl (Ph.D.student), Jan Gustafsson (lecturer), Hans Hansson (Professor), Mikael Sjödin (Ph.D.student), Wang Yi (lecturer).
The Department of Automatic Control and the Department of Computer Science, Lund Institute of Technology: Integrated Control and Scheduling Karl-Erik Årzén (lecturer), Klas Nilsson (lecturer), Patrik Persson (Ph.D.student), Anton Cervin (Ph.D.student).
Companies in the WCET Network
IAR in Uppsala, Olle Landström (development manager), Jakob Engblom (industrial Ph.D.student), Anders Berg (developer).
International Links of Interest
There are a number of WCET research projects worldwide. Here follows links to some of these.