[MiNT] 68k userland emulator, part #2

[Peter Persson <pep.fishmoose@gmail.com>]

Howdy,

I've updated my experimental 68k userland emulator for freemint.  
Again, it only runs on a 060 so the whole project is fairly pointless  
at this stage :) I hope to try it on my ColdFire EVB in the near future.

I decided to change CPU core. The CaSTaway core had some pretty nasty  
bugs which prevented working code from executing properly. I now use  
the proven Musashi core, which apart from being a lot more accurate  
also supports 020 instructions (I haven't enabled this in the emulator  
at this stage, since I will need to make sure stack frames etc are  
handled correctly first).

Speed is a bit slower now, since I evaluate every memory access,  
including instruction fetch etc. I will change this in the future, but  
I try to focus on compatibility first.

I've rewritten the internals to simplify porting. Instead of assembly  
wrappers and tunneling of OS calls, I now interpret each access to  
GEMDOS/XGEMDOS/BIOS/XBIOS and call the appropriate system call in  
source. This shouldn't be slower than the previous approach, and  
should ease porting a lot. There is some 68000 code in the project  
needed for the emulated CPU. I'm not quite sure how to handle that  
atm, but it should be possible to create the same effect in C by  
manipulating the CPU core.

Internally the emulator should be much cleaner now. Instead of  
intercepting TRAP exceptions I now use 68k handlers on the emulated  
side and trigger OS calls by means of the TAS-callback in the Musashi  
core. This means that apps can manipulate trap vectors freely, while  
still being able to call the original handler.

Compatibility is much better now, it seems like most well behaved  
stuff runs properly (but slow as a snail on valium). Pexec "GO"-modes  
are blocked at the moment. It is however possible to load a binary in  
to memory and to create a basepage.

Link: http://hem.passagen.se/shoggoth/misc/emu68k.ttp

Usage: ./emu68k.ttp <name of app> <commandline to app>

best regards

-- Peter