Software as part of the system, not apart from it
On most electrical and electronic programmes today, software isn't a separate concern bolted onto the hardware — it's where a huge amount of the system's actual behaviour lives. Treating it as an afterthought, reviewed only once the hardware is settled, is exactly how software-hardware interface problems end up discovered during integration instead of during design.
What it looks like in practice
We apply the same systems engineering discipline to software as to any other subsystem: requirements that are testable and traceable, interfaces to hardware and other software components defined explicitly, and verification evidence gathered as the software is built rather than assembled retrospectively. The aim is a system where hardware and software were engineered together, not integrated as a surprise.