jbn@glacier.STANFORD.EDU (John B. Nagle) (11/21/87)
Won't work. The M68020 has an on-chip cache which stores 32-bit address values. Even if the external memory addressing only uses fewer bits, the cache always checks all 32. On a system where the high address byte is unused by the memory, the following sequence will produce unwanted effects: Read address A. Write new value to A + 0xff000000 Read address A - get the OLD value! Like it or not, the M68020 is a 32-bit machine. John Nagle
daveh@cbmvax.UUCP (11/23/87)
in article <17223@glacier.STANFORD.EDU>, jbn@glacier.STANFORD.EDU (John B. Nagle) says: > Summary: Use of high bits in address for other purposes won't work on 68020. > > Won't work. The M68020 has an on-chip cache which stores 32-bit > address values. Even if the external memory addressing only uses fewer > bits, the cache always checks all 32. On a system where the high address > byte is unused by the memory, the following sequence will produce > unwanted effects: While AmigaOS turns the cache on on system startup, the Prolog interpreter could turn it off to avoid any problems related to the cache not wrapping. That's, of course, going to slow things down, but what can you do. > Like it or not, the M68020 is a 32-bit machine. And like I said before, what they really want here is a 40-bit machine. > John Nagle -- Dave Haynie Commodore-Amiga Usenet: {ihnp4|caip|rutgers}!cbmvax!daveh "The B2000 Guy" PLINK : D-DAVE H BIX : hazy "I can't relax, 'cause I'm a Boinger!"
mph@rover.UUCP (Mark Huth) (12/01/87)
In article <17223@glacier.STANFORD.EDU> jbn@glacier.UUCP (John B. Nagle) writes: > > Won't work. The M68020 has an on-chip cache which stores 32-bit So turn the cache off - oh, you want speed. Some people. 8-) Mark Huth