edit: also, hello marcan! tyvm for your work :D
From Sega v. Accolade - https://openjurist.org/977/f2d/1510
>We hold that when there is no other method of access to the computer that is known or readily available to rival cartridge manufacturers, the use of the initialization code by a rival does not violate the [Lanham Trademark] Act even though that use triggers a misleading trademark display.
I seem to remember a similar case for the Gameboy ROM that needed to contain an image of the Nintendo trademark to boot, but couldn't find a good online reference. Lexmark tried to pull a similar stunt by claiming the ROM code in their cartridge chips was executable code in a secret language, but courts again said it was an access control code first, and thus functional not creative.
If the comparison fails, the logo was still displayed scrolling down and making the bing sound, but the Gameboy now just halts. Everyone who had one in their youth knows the black block scrolling down with no cartridge inserted, and various variants of corrupted logos if contact was bad or the cartridge broken.
This also means the Gameboy has no “OS” whatsoever, it’s all done by the games. But the system is too simple to need one anyway.
That’s also why it’s so good for writing your first emulator.
But yes, the courts (or at least the 9th Circuit) have looked down on these attempts to use copyright and trademark as methods of preventing access. Of course now they have DMCA anticircumvention provisions to help out instead anyhow.
ModernVintageGamer knows his stuff well.
The world was a lot more reasonable before the DMCA.
My guess is that these methods involved some modchip-style tomfoolery like reset glitching or forcing values onto the bus, and could have been defeated by Sega in a future revision of the console.