Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!sdd.hp.com!elroy.jpl.nasa.gov!decwrl!mcnc!borg!oscar!tell From: tell@oscar.cs.unc.edu (Stephen Tell) Newsgroups: comp.sys.amiga.misc Subject: Re: Mac emulating Amiga Message-ID: <2864@borg.cs.unc.edu> Date: 3 Apr 91 04:11:53 GMT References: <9104012131.AA03364@covax.co.iup.edu> <1991Apr2.000456.26982@cunixf.cc.columbia.edu> Sender: news@cs.unc.edu Organization: University of North Carolina, Chapel Hill Lines: 45 In article <1991Apr2.000456.26982@cunixf.cc.columbia.edu> es1@cunixb.cc.columbia.edu (Ethan Solomita) writes: >In article <9104012131.AA03364@covax.co.iup.edu> student@COVAX.CO.IUP.EDU (student) writes: >Although >programs that directly access the hardware, even legally, on the >Amiga will crash on a Mac->Amiga emulator, any programs which >legally call the system can have hardware access "emulated", >although I can't account for the speed. >BTW: people who know better than I (no ego trips please 8) please >correct any misconceptions. Is it possible to trap all attempts >to use the hardware, even direct access? If the writers of an emulator wanted to, they could emulate the hardware exactly. Just use the MMU to trap accesses to the addresses of the custom chips, then when such a trap comes in figure out what custom chip register was accessed and simulate the register in software. This is much like using the Emulator traps on the 680x0 to run 68881 code without a real 68881 chip installed. Of course, this asumes that you have an '020 + MMU, '030, or '040. Even then, programs that count on the speed of a particular custom chip access are out the window, for example display hacks that write to the chips and expect things to happen on a precise per-frame basis. It may be too slow to be usable; you might have to patch the graphics.library rom image to go directly to the real display instead of to the simulated custom chips. I believe the correct term for this idea is a "virtual machine." You appear to have hardware, but you really don't. IBM was into this a lot for their mainframes. You can run several different operating systems on their own virtual machine all on the same physical machine. Multiple layers of virtual machines are possible. Look at an operating systems textbook for more info. The bridgeboard does somthing similar for the PC side. The PC display and I/O addresses are really just dual-ported memory, which is accessed from the Amiga side to give the illusion that there is hardware there. Its not quite the same because there is some hardware; the dual port memory and I think some stuff to give the Amiga an interupt when it needs to go find out what the PC side wants. -- Steve Tell tell@cs.unc.edu H: +1 919 968 1792 #5L Estes Park apts CS Grad Student, UNC Chapel Hill. W: +1 919 962 1845 Carrboro NC 27510 Duke Blue Devils: 1991 NCAA Basketball National Champions! We're Number 1 !! UNLV 90-91 record: "34 and DUKE."