An emulator, assembler, and disassembler for the Sega Game Gear
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  1. crater
  2. ======
  3. **crater** is an emulator for the [Sega Game Gear][game gear], with an included
  4. [Z80][z80] assembler/disassembler, written in C.
  5. [game gear]: https://en.wikipedia.org/wiki/Sega_Game_Gear
  6. [z80]: https://en.wikipedia.org/wiki/Zilog_Z80
  7. Why?
  8. ----
  9. While the internet is full of emulators for retro game systems, writing one is
  10. nevertheless a fun learning project.
  11. crater is named after [31 Crateris][crateris], a star that was – for a short
  12. time in 1974 – misidentified as [a moon of Mercury][moon]. Mercury was Sega's
  13. codename for the Game Gear during development.
  14. [crateris]: http://www.astrostudio.org/xhip.php?hip=58587
  15. [moon]: https://en.wikipedia.org/wiki/Mercury%27s_moon
  16. Installing
  17. ----------
  18. Only OS X and Linux are tested. You'll need a modern compiler that supports C11
  19. ([clang][clang] preferred) and [SDL 2][sdl2]. Using Homebrew, you can
  20. `brew install sdl2`; using apt, you can `apt-get install libsdl2-dev`.
  21. Run `make` to create `./crater`. To build the development version with debug
  22. symbols and extra diagnostic info (they can exist simultaneously), run
  23. `make DEBUG=1`, which creates `./crater-dev`.
  24. crater has a number of test cases. Run the entire suite with `make test`;
  25. individual components can be tested by doing `make test-{component}`, where
  26. `{component}` is one of `cpu`, `vdp`, `psg`, `asm`, `dis`, or `integrate`.
  27. [clang]: http://clang.llvm.org/
  28. [sdl2]: https://www.libsdl.org/
  29. Usage
  30. -----
  31. Running `./crater` without arguments will display a list of ROM images located
  32. in the `roms/` directory, and then ask the user to pick one, or enter their own
  33. ROM path. You can provide a path directly with `./crater path/to/rom`.
  34. Add or symlink ROMs to `roms/` at your leisure. Note that they must end in
  35. `.gg` or `.bin` to be auto-detected.
  36. Add `--fullscreen` (`-f`) to enable fullscreen mode, or `--scale <n>`
  37. (`-s <n>`) to scale the game screen by an integer factor.
  38. Add `--debug` (`-g`) to display detailed information about emulation state
  39. while running, including register values and memory contents. You can also
  40. pause emulation to set breakpoints and change state.
  41. `./crater -h` gives (fairly basic) command-line usage, and `./crater -v` gives
  42. the current version.
  43. ### Assembler/Disassembler
  44. crater has built-in support for converting Z80 assembly into ROM images, as
  45. well as attempting the reverse process (i.e., disassembling).
  46. `--assemble <input> [<output>]` (`-a`) converts source code into a `.gg` binary
  47. that can be run by crater. `--disassemble <input> [<output>]` (`-d`) executes
  48. the opposite operation. If no output file is given, crater will use the name of
  49. the input file, with the extension replaced with `.gg` for `-a` and `.asm` for
  50. `-d`. By default, this will never overwrite the original filename; pass
  51. `--overwrite` (`-r`) to let crater do so.
  52. Credits
  53. -------
  54. Special thanks to [SMS Power!][sms_power]'s excellent [development][sms_dev]
  55. section, which has been invaluable in figuring out many of the Game Gear's
  56. details, including ROM header structure and the memory mapping system. Various
  57. source code comments reference their pages.
  58. Also thanks to [Thomas Scherrer's Z80 website][scherrer] for many useful
  59. resources about the Game Gear's CPU, including info about
  60. [undocumented opcodes][undoc_ops] and [flags][undoc_flags]. Finally, credit
  61. goes to [ClrHome][clrhome] for their helpful Z80 [instruction table][clrtab].
  62. [sms_power]: http://www.smspower.org/
  63. [sms_dev]: http://www.smspower.org/Development/Index
  64. [scherrer]: http://z80.info/
  65. [undoc_ops]: http://www.z80.info/z80undoc.htm
  66. [undoc_flags]: http://z80.info/z80sflag.htm
  67. [clrhome]: http://clrhome.org/
  68. [clrtab]: http://clrhome.org/table/