https://github.com/fwsGonzo/gamebro/blob/master/POSTERITY.md
Many of the issues are not documented anywhere, and it is just about guessing what the hardware did - and thus, what the developers back in the day relied on!
The truth is it's rather tedious. There are 256 opcodes you will need to create. Each has certain flags you will need to check that change it's operation.
Some of those flags are undocumented, and several of the opcodes actually have hardware level bugs that make them act differently than the CPU document describes.
So after creating every opcode, you will inevitably have bugs which you need to fix.
After fixing those you will still not have games running because of so many undocumented/buggy opcodes, so now you need to figure out how an actual gameboy operated.
At this point I was only able to solve it be getting a working emulator and executing the same program on each until their states diverged.
I did find it interesting to learn about low level hardware, but I'd say the project is 50% reading specs, 10% interesting, and 40% tedious pain-in-the-butt.
I never did get sound working, and the graphics are buggy, but I think I got far enough that I learned all there was to learn.
They don't, whatever documentation you used was either wrong or based on the Intel 8080 or Z80 instead of the Sharp SM83 core that's actually used in the original Gaemboy.
I am googling it now, and there are some forum posters saying ' don't use that, it's old and not completely accurate' but it was all that I could find at the time.
I'm aware that it's not official documentation, but you have to remember this was over 10 years ago--there might be better resources now.
It's from the same era as the Game Boy Color and has some interesting features (serial communications between devices, and the infamous "tab cheat" that momentarily disconnecting the battery with a plastic tab to randomize the memory contents).
Interesting how Pokemon is widely emulated, but nobody ever bothered with Digimon. There has been multiple generations of Digivice hardware, so best start at the original.
I'd like to see somebody take on the reverse-engineering challenge. I don't think there's even a ROM dump yet.
They've actually started selling new stock recently (20th Anniversary Digivice), including at retail stores for around $30 each.
That said, MAME drivers for most home consoles and computers already exist since the MAME and MESS projects merged.
