Clearly, 100 ECUs will not operate entirely independently – they will have to communicate with each other. And indeed, such communication was facilitated by the hardware and signal deployment architecture. However, the relationship between interdependent ECUs was loose and informal, i.e there was little software system architecture. For example, it was well known that within the software “architecture” of a particular range of vehicles, there were eight different sources of speed measurement.
Treating software as a separable vehicle component has worked for the last twenty years, allowing automotive OEMs to continue designing and building complicated vehicles by utilising their supply chain. Tier one suppliers could pursue their given goals, loosely coupled with other suppliers, with the OEM merely integrating and testing the associated deliverables. In previous generations of vehicles, less than 10% of the in-vehicle software was produced by the OEM for whom I worked, the rest being sourced from multiple suppliers.