Comparison of Approaches to the Test of Control Unit Software

Introduction Control units in a safety-critical area must fulfil a lot of requirements concerning the reliability and the robustness. These requirements must be fulfilled in a raising magnitude by the control unit software. To guarantee the compliance of these requirements, the control unit software is tested with external malfunctions, as for example due to noisy sensors, disturbed communication or corrupt actuators. [1] Besides, the software under test is coupled with a simulation of the dynamic system behaviour. So, it is necessary to execute the tests in a closed control loop. According to the kind of the coupling between software under test and environment we have to distinguish between "hardware in the loop" (HiL), "processor in the loop" (PiL) "software in the loop" (SiL), and “model in the loop” (MiL) tests. Within the scope of the project SiLEST the SiL test approach is compared to the HiL test approach. The test approach is evaluated with regard to the applicability and recommendations are given for the application of the test process. This article explains the different test approaches and gives an overview of the SiLEST test execution environment developed for the SiL test. The test environment permits the automatic execution of tests of control unit software without manual interventions. Afterwards we describe our experiences with the new test approach which we made with the testing of an automotive engine management system and an attitude control system of a small satellite. Finally we give in these paper recommendations for the application of the different test approaches.