Approximate Worst-Case Execution Time Analysis for Early Stage Embedded Systems Development

Abstract

Abstract.A Worst-Case Execution Time (WCET) analysis finds upper bounds for the execution time of programs. Reliable WCET estimates are essential in the development of safety-critical embedded systems, where failures to meet timing deadlines can have catastrophic consequences.Traditionally, WCET analysis is applied only in the late stages of embedded system software development. This is problematic, since WCET estimates are often needed already in early stages of system development, for example as inputs to various kinds of high-level embedded system engineering tools such as modelling and component frameworks, scheduling analyses, timed automata, etc. Early WCET estimates are also useful for selecting a suitable processor configuration (CPU, memory, peripherals, etc.) for the embedded system.If early WCET estimates are missing, many of these early design decisions have to be made using experience and "gut feeling". If the final executable violates the timing bounds assumed in earlier system development stages, it may result in costly system re-design. This paper presents a novel method to derive approximate WCET estimates at early stages of the software development process. The method is currently being implemented and evaluated. The method should be applicable to a large variety of software engineering tools and hardware platforms used in embedded system development, leading to shorter development times and more reliable embedded software.

Modelling bus contention during system early design stages

“…Then we measure models accuracy when predicting contention time (et muc j ) when each BCM is integrated with the CCM [7]. In both cases we measure inaccuracy by comparing observed and predicted values as presented in Equation 13.…”

“…To that end they use a mixture of measurements and modelling [15] [13]. In [15] measurements are used to calibrate its models, and similarly [13] uses measurements and combines them with regression models to obtain their estimates. Other approaches use simple single-core processor designs that are more WCET friendly [10].…”

Improving Early Design Stage Timing Modeling in Multicore Based Real-Time Systems

“…Therefore, obtaining early and tight estimates of ∆t is of great help to reduce the risk of LDP changes. There is a general consensus in the literature [11] [14] that during the EDP accuracy of the timing estimates is not the only metric to consider, with tight upper-bounding estimates being rather required for LDP. Instead, the speed to obtaining those estimates plays a key role to allow engineers to explore a vast set of design choices in a timely manner.…”

“…For instance, authors in [17] work on the concept of C-source-level abstract machine which is calibrated based on measurements to match a target real hardware. In this line, [14] proposes the timing model code level that combines measurements and a regression model to perform timing estimates of source code. In this latter work, the timing (cost) model is built, i.e.…”

“…Previous works show that, while exact bounds are required in LDP, during EDP, instead, approximations to those bound are needed [11] [14]. Some accuracy is traded to speed up the estimation process so that engineers can make design space exploration taking into account timing.…”