Metroid Disassembly

Metroid is a hugely popular side-scrolling action adventure game developed and published by Nintendo for the NES.

This disassembly project is a quick experiment to see how the Metroid cartridge would work with SourceGen. This is not a finished disassembly. The original disassembly project upon which this is based came from metroid-database.com/source-code and nicholasmikstas.com/games, but neither of those sites work anymore. The nmikstas/metroid-disassembly github repo appears to be the current home.

Disassembly listing of the game.
Project file without binary (requires SourceGen v1.9 or later). You will need to find a matching iNES ROM image to do anything useful. The image file is called "Metroid (USA).nes".

Notes

Metroid presents an interesting challenge for a disassembler. In memory, the ROM has two 16KB segments, from $8000-bfff and $c000-ffff. However, the cartridge actually has 8 16KB segments, 7 of which are mapped to the same place:

#	Addr	Name
0	$8000	Title
1	$8000	Brinstar
2	$8000	Norfair
3	$8000	Tourian
4	$8000	Kraid
5	$8000	Ridley
6	$8000	Graphics
7	$C000	Game Engine

While SourceGen is designed to handle multi-segment files, Metroid presents an awkward situation. Segments 1-5 have code that is called directly from the game engine, at a specific address that isn't part of a jump table. For example, the instruction at $f503 is JSR $80b0, where $80b0 is a small subroutine in segments 1-5. Unfortunately, in segment 0 $80b0 is actually the middle of an instruction, and without guidance that's where SourceGen tries to map it. Marking segment 0 as "no inbound references" avoids most of the issues, though it's necessary to fix an actual bank 0 reference from the game engine at +01c1fa by providing an operand label.

Another issue is the fact that a 128KB file is a bit large to display as a single document. The approach used in the original disassembly -- splitting each segment into a separate source listing -- works better. (Plus, most of the cross-assemblers choked on the generated sources because they exceeded the 64KB bank limit... dividing it into separate source files and linking the output together would solve that.)