As DO-178B was updated to DO-178C it was decided that the increasingly popular model-based development should be made available to compliant applications, and that they should be addressed by a supplement, DO-331, “Model-Based Development and Verification Supplement to DO-178C and DO-278A”.

DO-331 takes the approach that specification models or design models take the place of high-level and low-level requirements respectively. Textual requirements may be linked to models upstream or downstream (Figure 1).

Figure 1: Model Usage Examples, based on table MB.1.1 from RTCA DO-331

Popular tools such as MathWorks® Simulink®, IBM® Engineering Systems Design Rhapsody®, and ANSYS® SCADE can generate code automatically. DO-331 MB.5.0 (Software Development Processes) addresses traceability, model standards and more for both software requirements and design processes where such tools are used. MB.5.3 (Software Coding Process) is merely a cross-reference the equivalent section in DO-178C, underlining the fact that best-practice coding-related process activities still apply whether code is hand-coded based on a set of textual requirements, hand-coded based on design models, or auto-generated from a tool.

Projects using auto-generated code almost always contain some hand-code too, and often include legacy hand-coded components. It is possible to apply different coding standards to these different code subsets , such as MISRA-C 2012 for hand-code, MISRA-C 2012 Appendix E for auto-generated code, and a custom coding standard for legacy code.

DO-331 MB 6.0 (Software verification process) expands on how best practice applies to MBD, with DO-331 MB.6.8.2 (Model Simulation for Verification of Executable Object Code) expanding upon which verification objectives can be partially satisfied at the model level, and which must be performed at the target level.

Background