Mappy VM is a fully featured virtual machine which behaves very similar to the Gameboy Advance from Nintendo. It fully supports the CPU, input hardware, all graphics modes, DMA with correct timing, and many aspects of the sound system. Both a compiled version and the complete source code can now be downloaded from the Mappy VM website. However, it needs a BIOS image from a GBA for proper operation, as the included stub BIOS only includes an IRQ handler.
Mappy VM also provides an extensive suite of tools to assist developers in debugging and developing their games:
- Breakpoint List
- IO Register Viewer
- Memory Editor
- Palette Viewer
- Sound Viewer (prototype)
- Source Debugger
- Sprite Viewer
- Video Viewer
- Watch List
All of the viewers are updated in realtime as the simulation progresses, and most of them have editing capabilities. Being able to pause a simulation and edit system conditions can be extremely useful in attempting to reproduce bugs. In addition, Mappy VM also supports
saving or restoring the entire system state, making it easier to debug problems that only occur after several minutes of gameplay or to test multiple hypotheses.
A number of pictures from the current version (0.9) can be seen in the online help.