Evaluation of Methods for Dynamic Time Analysis for CC-Systems AB

2 Nowadays, up to 98% of all manufactured computer processors worldwide are used in embedded systems. Most of the embedded systems have time constraints, which means that the computer that controls such a system not only has to compute the correct result, but is also required to produce the correct result in a specific time interval. The time constraints are often expressed by temporal deadlines that must be met by the software tasks in the system. It is therefore important to know how long time the system needs to execute each individual task. The worst-case execution time (WCET) is an upper bound for all the possible execution times of such a task. The WCET can be obtained by various kinds of methods. Generally, they can be divided into two categories: dynamic methods and static methods. Dynamic methods derive the WCET by measurements. The program code executes, and the execution time is measured by hardware or software, such as a logic analyzer and time-functions provided by the operating system. Static methods obtain WCET without executing the program, instead a WCET analysis tool is used to calculate the execution time for the longest execution path. In this thesis the WCET was measured by dynamic methods. An oscilloscope and a logic analyzer were used for time measurement. The goal of the thesis was, together with CC-Systems AB (CCS), to compare and evaluates different kind of methods for execution time measurement. The WCET analyses have been performed on interrupt routines used in CCS’s welding machine control system. In order to find out the differences in precision and practical difficulties between using measurement and static analysis, the measurement methods and their results were compared with WCET estimates obtained by the static method, the aiT WCET analysis tool. To estimate WCET by a static method was a part of work in another Master Thesis, which was performed by Ola Eriksson at CCS during the same period of time as this thesis. Through this thesis, we found out that neither the dynamic measurement nor the static WCET analysis is alone perfect. To obtain the best WCET estimates, the recommendation is to combine both kinds of methods.