A Reference on the layout and structure of GameBoy Color Roms?
Does anyone have a reference or source about how GameBoy Color roms are laid out - where the data and code, what machine code instructions are used, how the clock works etc? I'm interested in perhaps building an emulator myself but I can't find any information about the roms' setup other than looking at them in a hex editor. I'm interested in roms in the .gbc file format.
I can of course look at the source of a working emulator, but I'm interested in something a bit more high level than that while I'm starting off.
Edit: Here are a load of really good resources I found:
- A Emulator being built in javascript with more up to date source.
- "The PAN documents" a detailed spec of the gameboy
- A more up to date and better version of the previous item, with loads of stuff. Best resource.
- Standard Z80 opcodes
- All the opcodes in the Gameboy Z80
- A list of opcodes changed/removed in the Gameboy
- Z80 user manual (useful for flags)
- Discussion of differences between Gameboy Color Z80 and 8080/Z80
- Massive site dedicated to gameboy architecture (+GBA)
- Another document on GBSpec, with timings
Also, see the source for my currently developing project and this finished one in C# for the Gameboy Classic (more docs)
Answer
ROM header from 0x100 to 0x14F. Everything else is "the ROM" meaning instructions interlaced with data or whatnot.
https://web.archive.org/web/20141105020940/http://problemkaputt.de/pandocs.htm
The opcodes are custom designed to be like the Zilog Z80, but are not exactly like it, since the CPU die itself is different from that of a Z80 as well as the clock cycles and register F flags being entirely different.
Snoop around in my code to find out the operations. https://github.com/grantgalitz/GameBoy-Online/blob/master/js/GameBoyCore.js look at line 525 and below. The GameBoy Color emulator is in javascript FTW.
And Imran's emulator is a bad source for looking up how the opcodes work, because his emulator still has many problems with getting the opcodes right. Look at gambatte's source code for the most accurate (accurate and "some more") depiction of how the console works.