Partitioning: How far do you need to go?

Software Partitioning is now commonly used in safety systems to either allow the integration of software components developed at different Software Design Assurance Level (DAL - Design Assurance Level as per DO-178C / ED-12C [1]) or to gain more flexibility to perform system updates by limiting its impact. In all cases the expected benefit is a reduction of the overall system cost including the hardware, the initial certification, the system maintenance, the recertification in case of change, etc.. Different approaches are possible to implement and demonstrate software partitioning, each having pros and cons. The objective of this paper is to present the partitioning constraints, with respect to avionics safety certification and how the different implementations affect the system level design, along with project budgets. The paper looks at different grades of partitioning, with use cases as examples, detailing them to compare and contrast the different options.