gnu@l5.uucp (John Gilmore) (12/03/85)
In article <249@mips.UUCP>, kim@mips.UUCP (Kim DeVaughn) writes: > > > Sounds like it could make the Amiga into a SuperAmiga! Now if we could > > > just clock the thing at 16.7MHz (or even 12.5MHz). > > As long as Amiga didn't do anything wanky like counting on the AS-DS delays > > or the DS-/AS delays you should be able to supply the 68020 with a "private" > > clock source. And since the 680xx is an async design when it goes outside > > of the private 256k ram it should slow down. Probably the Amiga really does depend on all those unspecified delays. When you're trying to cram 3 RAM cycles into every CPU memory cycle, you use all the kludges you can... In any case, it should be possible to run a 68020 at exactly twice the standard clock rate of the Amiga (or any other 68000 system). This would make the interface synchronous to the rest of the Amiga board and you could tune the timing of the various signals to match what the Amiga expected. Given that a 68020 cycle would take 3 new-clocks and a 68000 cycle would take 8 new-clocks, there's plenty of time to fiddle with generating all the right fake strobes. If you took the time to test it on all of them, you might even be able to build one piggyback board that would run in a Mac, Atari, or Amiga, by emulating the 68000 timing exactly enough. > I've not worked with 680x0's until now ... is also possible to run a 68881 > with a fast '020 (I don't *think* fast 881's have been announced yet)? You can run the 68020 and 68881 on totally independent clocks. It uses standard (wait for DTACK) bus cycles to talk back and forth.