Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!think.com!mintaka!geech.ai.mit.edu!rjc
From: rjc@geech.ai.mit.edu (Ray Cromwell)
Newsgroups: comp.sys.amiga.emulations
Subject: Emulator Mechanics
Message-ID: <1991Mar7.093149.18707@mintaka.lcs.mit.edu>
Date: 7 Mar 91 09:31:49 GMT
Sender: daemon@mintaka.lcs.mit.edu (Lucifer Maleficius)
Organization: None
Lines: 47


 I got an idea. How about combining both methods? (compile and interpret)

 First compile the executable with flow analysis into 68k code. Any
instruction that tries to touch a hardware register will become
a trap instruction(or use an MMU to trap it) to emulate the hardware.

  Where does the interpreter come in? Any code that tries to self modify
or do a change of state (table lookup, indirect jumps, etc) with be
interpreted.

 Sounds hard? You bet. The easier solution of all is to throw faster
CPUs at the problem.


Now for another question:

 Why doesn't AMAX multitask? It should be EASY to run multiple copies
of the Mac ROM as a task (since its a rom, its mostly pure code, except
each task would need to alter where the ROM things the system memory is.)

 For things like the Atari emulator, or another 68000 emulator, the compile
technique should work great! Just recompile the parts of the code
that bang on the hardware, or use an MMU to trap them.


The whole compilation process is made easier when the machine
your trying to emulate has an object code format that contains
seperate data and code chunks, and perhaps some relocation data.
Further more, if the machine has rules against self modifying code,
and a device independent OS it becomes trivial.

Could someone run SI or dhrystone on IBeM and tell me how it performs?
Itis said that SoftPC on a Mac @25mhz 68030 runs at 6mhz AT speed.

Does anyone know if IBM code uses self modifying code, or
jump tables? What kind of code does their compilers produce?
And, does the IBM has a special object code format that seperates
code and data?


The compilation technique could work well, but the compiler would have
to be VERY smart in its flow analysis of detecting code/data, jump
tables, self modifying code, PC counter and stack manipulation, etc.

I'll clairfy my thoughts tommorow, it's going on 4:30am here, and I 
need to get some well deserved sleep. :-)