mjp@spice.cs.cmu.edu.UUCP (04/03/87)
Keywords: beilke@puff.WISC.EDU (Matthew Beilke) writes: > The ST can not emulate an Amiga, simply because it does not have the > graphics/sound harware to do everything an Amiga can. However, the Amiga > could in theory emulate an ST (It would obviously be _much_ slower than > an ST. > > BTW, a real ST emulator is indeed quite feasible. After all they > both use the MC68000, don't they. The hard part would be to get AmigaDOS > to read TOS disks. > > - - - ---> Matt Beilke <--- - - - Actually, reading TOS disks would be the easiest part. The Amiga disk controllers read raw data via DMA and the trackdisk.device decodes the MFM information using the blitter -- the amiga does not use any off-the-shelf disk controller chip. The upshot of all this is that the Amiga can read/write any 3 1/2" constant speed disk format (sadly, it can't read/write variable speed formats as used by the Mac. At one time I had the idea of writing a Mac/Amiga/ST file converter). As far as emulating an Amiga with an ST, impossible. The 640x400 interlace modes (with 16 colors), HAM mode (all 4096 colors), the hardware sprites, the 4 D/A converters for sound generation, etc. would be impossible to generate on the ST. Remember that many things that happen in hardware on the amiga are precisely timed, such as bus arbitration, and would be tough to emulate in software (especially on hardware that is running about the same speed as the system you are trying to emulate). You could make an ST emulate the Amiga OS, and run programs that don't depend heavily on the graphics display, but I'm afraid that would get you about as far as the AmigaDOS commands for manipulating files. As far as emulating the ST with the Amiga, that would be tough as well. The hardware for the two machines support displays rather differently. The Amiga uses a bit-plane oriented approach, the ST uses a linear arrangement that I don't remember the details to (yes, I'm an Amiga hacker, but I try to keep up on the rest of the world as well), but would be nasty to have to re-map to fit the Amiga display hardware (as in prohibitively slow). According to what I hear about the A2000, it takes a decent amount of Amiga power to keep up with the PC display emulation. The ST would be that much harder. Also, the Amiga can only access display and audio memory in its lower 512K, while the ST does not suffer from this restriction. That would also hamper efforts to make an Amiga successfully emulate an ST. The reason why it is so easy to emulate the Mac using Magic Sac is that the Mac is mainly a software-driven system. The Mac is basically a 68K, some memory, I/O ports and a bitmapped display. The software is what makes it run. Move that software to a machine that also has a 68K, memory, I/O ports and a bitmapped display and voila, you're emulating a macintosh. The ST and the Amiga both have more sophisticated hardware, and it's the nifty tricks in hardware that are SO difficult to emulate in software. -- Mike Portuesi / Carnegie-Mellon University Computer Science Department ARPA: mjp@spice.cs.cmu.edu UUCP: {harvard | seismo | ucbvax | decwrl}!spice.cs.cmu.edu!mjp BITNET: s314mp1u@cmccvb, rainwalker@drycas (pick one) "Amiga hackers do it graphically, with lots of sound effects" "Mac owners dream in black and white Atari owners dream in color... but Amigoids dream using Hold and Modify!"
sansom@trwrb.UUCP (04/03/87)
In article <1175@spice.cs.cmu.edu> mjp@spice.cs.cmu.edu (Michael Portuesi) writes: >As far as emulating the ST with the Amiga, that would be tough as >well. The hardware for the two machines support displays rather >differently. The Amiga uses a bit-plane oriented approach, the ST >uses a linear arrangement... The ST's display does, in fact, use memory mapped bit-planes. The number of planes it uses is, of course, dependent on the screen resolution. Low resolution (320 x 200, 16 colors) uses four bit planes _interleaved_ in memory (not linear), medium resolution (640 x 200, 4 colors) uses two bit planes, and high resolution (640 x 400, 2 "colors") uses one bit plane (which is, in effect, a linear arrangement). -Rich -- /////////////////////////////////////\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ /// Richard E. Sansom TRW Electronics & Defense Sector \\\ \\\ {decvax,ucbvax,ihnp4}!trwrb!sansom Redondo Beach, CA /// \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\/////////////////////////////////////