Here is another real-life scenario. Host talks to the first Chip-1 over a standard and wide interface. The host was also supposed to talk to Chip-2 over the same interface. Chip-2 was pin constrained, so it was decided to connect Chip-2 to Chip-1 and create a copy of config and status registers on Chip-1 so that host can read it.
Can you design a very simple interface between these two chips with just 2-3 wires? Power is not an issue. Timing is not an issue as the frequency is low around 100MHz. The goal is to create a quick and dirty solution.
Ignore I2C solution as you don't want to invest time in buying IP and integrating it.
