From: David Wood (jbevren_at_starbase.globalpc.net)
Date: 2002-07-29 13:24:55
En contrare my friend. :) The 65816 (and the 65802?) has lines that determine when memory's being accessed versus random blind accesses. Have a close look at the documentation, and you'll see tis even possible to determine if the memory being fetched is program or data, or even further, interrupt vectors. ;) -David On Mon, 29 Jul 2002, Nicolas Welte wrote: > Hi Nick, > > firstname.lastname@example.org wrote: > > Could you identify which chips/pins these other wires go to? Do you think > > that this would be a easy way to also engineer a faster 65802 CPU into the > > C128? In the past I tried doing something on the by multiplying the clock > > phase on the 8502 side, but as the RAS and CAS signals are produced by the > > VIC it would crash. How does the Z80 get away with it? > > Reengineering this device is one thing on my to-do list, of course. First > comes building that GAL-Blast device to read out the GAL, if it isn't > protected. > > As I understand the circuit, it runs the Z80 at 8MHz until it requests a > memory access. Then it is halted by the GAL until it is time for Z80 memory > accesses. The original Commodore way is different: The Z80 is run at 4MHz > half of a 1MHz Phi2 cycle, and during the other half it is halted completely > to allow for a memory access, not matter if it is needed or not. > > This only works for the Z80 with its extra status lines that signal memory > and i/o accesses, with a 6502 family member you're out of luck with such a > simple approach. IMO the speedup for the Z80 will only be effective for > opcodes that eat up a lot of cycles. Short opcodes with lots of memory > accesses will be as slow as ever, I guess. > > A few days ago I also found an advertisment for this device in an old 64'er > issue from '89: The device was sold by Rossmöller for DM 99, they also had an > 8MHz CP/M cartridge for the C64, which also sold for DM 99! An 8MHz CP/M > cartridge for the C64 was also published by c't magazine: > http://www.ix.de/ct/inhverz/search.shtml?T=z80+c64&Suchen=suchen > > For a faster 6502 you have to do it just the other way around: Run the 6502 > on its own fast memory subsystem and give the VIC/DMA system some memory > access slots to this fast memory. You have to buffer the data for the slow > VIC with latches, so the data that is fetched at 8MHz is still accessible to > the 2MHz device. > > Nicolas > > Message was sent through the cbm-hackers mailing list > Message was sent through the cbm-hackers mailing list
Archive generated by hypermail 2.1.4.