Welcome back Cherryroms!
Cherryroms
I’m not writing this post just out of personal nostalgia though. It was also on Cherryroms that neviksti first posted about his efforts to decapsulate a Game Boy CPU an extract the DMG-01 256 byte internal bootstrap which is used to check the Nintendo logo and checksum on a cartridge before deciding to allow booting the cartridge. The function of the bootstrap was known and even documented in a patent however the actual memory content had never been dumped up to that point, so neviksti’s effort brought something new to the table.
The original thread can now be read in its entity again on Cherryroms here or archived here.
So does that mean we can make a custom bootstrap that silently boots?
Nope.
To read the bootstrap you need to melt the top of the chip to visually inspect the individual transistors. To modify the bootstrap you also need to get into the chip, and modify said transistors. Certainly theoretically doable. There are even companies that do this commercially. (Mostly to break the security of things like smart cards and stuff like that) But it’s complicated and expensive. So you’ll have to stand the beep, or keep piggging.