A gameboy (color) emulator in NIM written as language learning excersise.
The gameboy is broken into modules per internal function. gameboy.nim
coordinates the system level operations and issues a step for the system
by telling the CPU to execute a single operation.
The CPU returns how many system cycles it took to execute a sepcific opcode and the gameboy then executes that many internal cycles to the other modules. Maybe one day I'll figure out "real" clocking but that drastically increases the difficulty of the system.
There's a very limited debugger at the moment. Debugger will match on the first part of a string if a small string is shown. Optional parameters are prefixed with a question mark.
Example: step 888 is the same as st 888 and st will be listed below.
- load - Loads a rom. There is none in source control
- st <?NumSteps> - Issues the number of steps in opcode execution or a single step if arugment is empty.
- bp <###> - Sets a breakpoint. NOTE: This assumes the input is hex and NOT prefixed with
0x - tf <z|n|c|h> - Toggles a flag on or off.
Gameboys utilize memory-mapped IO and interfaces to other modules.
memory.nim serves as an interface to the CPU / other components
that abstracts away which modules to talk to. It is essentially
a proxy to other module read/write functions.
For modules that vary memory locations (such as paging ROM memory) the modules themselves handle the pagination functions.
cartridge.nim is responsible for loading the ROMs to execute and
offers up some methods for reading and writing to memory within
the cartridge. Paging between different ROMs or other functions of
the MBC are handled here.
Is there anything unique about this one?
Maybe? I tried to implment the "real" PPU pipeline which is fudged
by many other emulators since the entire operation was not understood
at the time. See the Ultimate Gameboy Talk in references for more
information on how this works.
Why another gameboy emulator?
It's fun and I wanted a new programming challenge.
How many games does it support?
None at the moment. My goal is Pokemon Blue / Red. Past that I don't know.
The following are very useful for learning about the gameboy. Note that many documents disagree with each other. It's up to you to find the "truth" of the Gameboy!
The ultimate Gameboy Talk - Required watching!
Gameboy CPU SM83 Instruction Set
Pan Docs - "The single, most comprehensive technical reference to Game Boy available to the public."
Blargg's Gameboy Hardware Test ROMs
Game Boy: Complete Technical Reference
Gameboy CPU Manual - Use with care, I've been read there are mistakes