Hi! I'm new here, and am very interested+motivated to understand exactly how the ECU works.

If somebody could link some technical resources or even explain themselves, that would be much appreciated :)

A large part of what I'm asking can be boiled down to: if a completely new sensor was added to an engine, and gave information f(t), how can an ECU be programmed to manipulate and react to this information?

For example, how is the software written that takes in oxygen sensor data and subsequently adjusts quantities of fuel to be injected? What does the actual process of designing and writing an ECU look like? What file formatting is used?

In a car with lots of custom parts, how can a working ECU+software be developed rapidly?