...to the point where there are transistor-level simulations of the CPU and PPU:
http://www.visual6502.org/JSSim/
https://wiki.nesdev.com/w/index.php/Visual_2C02
The only other game console I'm aware of a public transistor-level simulation for is the much more limited Atari 2600:
https://github.com/gregjames/Sim2600
...to the point where there are transistor-level simulations of the CPU and PPU:
http://www.visual6502.org/JSSim/
https://wiki.nesdev.com/w/index.php/Visual_2C02
The only other game console I'm aware of a public transistor-level simulation for is the much more limited Atari 2600:
https://github.com/gregjames/Sim2600