moa VS freebee

The code is here if you're interested: https://github.com/transistorfet/moa System is the top level component and devices.rs has the traits that System uses to interact with the components. The machines directory has the system definitions that build a specific machine to emulate.

A few months ago, I wrote a 68000 emulator in Rust named Moa. My original goal was to emulate a simple computer I had previously built. After only a few weeks, I had that software up and running in the emulator, and my attention turned to what other platforms with 68000s I could try emulating. My thoughts quickly turned to the Sega Genesis and without thinking about it too much, I dove right in. What started as an unserious half-thought of "wouldn't that be cool" turned into a few months of fighting documentation, game programming hacks, and my sanity with some side quests along the way, all in the name of finding and squashing bugs in the 68k emulator I had already written.

There's not much to it. Only one window can be created at the moment, and input is not yet supported. The threaded option is also not shown here. Before long, the code grew more complicated, and now includes parsing of command line arguments with the clap crate. To see the latest version, check out the Genesis machine-specific binary and the MiniFB host impl and main loop

Since the 68000 has a reasonably orthogonal instruction set, we can break down the opcode word into sub-components, and build up instructions by separately interpreting those sub-components, rather than having a match arm for each of the 65536 combinations. There is a really helpful chart by GoldenCrystal which shows the full breakdown of opcodes for the 68000. We can look at the first 4 bits of the instruction word to separate it into 16 broad categories of instruction, and then further break it down from there. The full code can be seen here

If you want to try out a UNIX PC, the FreeBee emulator can be used with two different hard drive images that have been made available. Though you will have to compile FreeBee as there aren’t any packaged releases.