Automating WCET Analysis for DO-178B & DO-178C

Determining worst-case execution time (WCET) is a recommended activity for avionics systems developed according to the DO-178B or DO-178C guidelines. This white paper assesses the current state of practice for determining WCET when working to these guidelines and introduces the benefits that arise from being able to automate this process. With its DO-330 qualification kit, RapiTime (part of the Rapita Verification Suite) is unique in allowing these benefits to be realized for DO-178B/C developments.

Determination of worst-case execution time (WCET) is an activity that is recommended in DO-178B and DO-178C 6.3.4f. Here we consider the current state of practice for determining WCET and present the benefits available from automating the process. Thanks to its DO-330 qualification kit, RapiTime uniquely allows these benefits to be realized in DO178B/C projects.

RapiTime is a tool to determine the execution time of embedded software. It reports measured maximum, high water mark and calculated worst-case times. The WCET calculation is based on measured data, annotations and the source code structure.

To use RapiTime’s calculated WCET in support of DO-178B or DO-178C objective 6.3.4f, it is necessary both to qualify the tool and to provide a corresponding analysis process.

One approach to determining WCET that is widely used and currently accepted by certification authorities is manual analysis and measurement. Manual analysis and measurement is an effort-intensive task and requires an extremely high level of care to ensure measurements are correctly captured.

By using automation to reduce the level of effort required and increase the accuracy of results, RapiTime represents an evolution of the manual analysis and measurement approach. With the introduction of the DO-178B/DO-330 qualification pack, RapiTime can replace manual activities in projects requiring DO-178B/DO-178C certification.

The development of the new qualification pack means RapiTime is the only tool in the marketplace capable of measurement-based WCET analysis for DO-178B.

This white paper describes:

• What is required for WCET in DO-178B and DO-178C projects.
• The current state of practice, and its limitations.
• How RapiTime represents an improvement on the state of practice.
• How to use RapiTime in a DO-178B or DO-178C environment.