Implementation of the SMILE SXI instrument application software

Instrument control and data handling are critical aspects of every space mission, taken care of by flight software. We are implementing the instrument application software (IASW) for the Soft X-ray Imager (SXI), one of four science instruments onboard the SMILE satellite - an ESA/CAS mission currently in development with the goal to study the interface between the solar wind and Earth's magnetic field. Our IASW runs on the digital processing unit of the instrument and can be essentially divided into three components. While the basic SW as the low-level layer comprises the operating system and drivers (e.g., for the SpaceWire connectors), the application SW provides all high-level services for the instrument, and the data pool facilitates visibility and control over the software. The main functions of the IASW include commanding of the detector front-end electronics and operation of the radiation shutter electronics, telemetry data compression, housekeeping management and storage, as well as maintenance of general instrument health. Furthermore, the software shall be able to perform (to some extent autonomous) fault detection, isolation and recovery. The IASW is mode driven, i.e. it operates several state machines and provides algorithms and procedures to maintain instrument operation. These parts are implemented via the CORDET framework. Our software development follows a test-driven design - we have therefore also created a suite of tools that facilitate interaction with flight software, speed up the process of test generation and verification, and provide a modular environment comprising actual hardware and simulator components.