Michael J. Mahon wrote:
I agree that using multiprocessing speedup for scrolling is a win, compared to doing it all on one processor or the other. As you note, there are severe interference effects with the Softcard, but it also allows the 6502 to make progress while the Z80 is running, since the Z80 doesn't make use of all of the memory access slots.
AFAIK 6502 was always held off-line while z80 was running. The only exception was a z80 "memory refresh" cycle when 6502 was given a chance to fetch a byte to refresh its dynamic registers, byte this byte was ignored anyway as "ready" was not asserted.
-Alex.