Hello and welcome to another episode of “Applied FuSa,” a podcast for FuSa pragmatists.

Functions are often broken down into sub-functions. A typical reason for this is that it can be easier to implement sub-functions rather than the complete function.

This strategy is relevant to functional safety for two reasons:

1. Depending on how the function is broken down into sub-functions, the ASIL of the sub-functions may be reduced; and

2. The usually lower complexity of sub-functions not only reduces the validation effort but also the risk of failure.

In ISO 26262, this type of breakdown is referred to as requirements decomposition, provided the sub-functions meet certain criteria — for instance, complete independence. In this episode, we will present the exact requirements for such a requirements decomposition in detail, explore its benefits, and discuss its limitations.