Edwin Blink wrote: > From: Geoff Winkless <[EMAIL PROTECTED]> > >> Without wishing to appear stupid (yeah, I know, too late, haha), I'm >> still not clear why that's a memory access. > > It's not. The delay is added there for convenience. But in fact it > will delay the next > opcode fetch (unless it is in rom but read below). > >> Shouldn't that round up to 4,4,8,8,5 if in ROM with display >> contention >> and 4,4,4,8,5 with RAM contention? > > The delay shifts to the next (HL) cycle on next LDIR.
Whuh? > the RAM can be accessed once every 8T during display(PAPER for Ales) > contention and once every 4Ts during RAM contention But there will be no RAM access for 8 t-states after the ,5 - the 4,4 will take 8 t-states, so the RAM will be available again. If what you're saying is that actually everything is broken down into chunks of 8-t-states _regardless_ of whether there's a memory access, then that's a bit more understandable... _However_, what that actually means is: If instructions in []s are ROM-based (or internal) and in {}s are RAM-based (therefore must be 8-state aligned): [4],[4] (one block) -- 8 cycles {3} (one block) -- 8 cycles {5} (one block) -- 8 cycles [5] + [3 of 4] (one block) -- 8 cycles [remaining 1 of 4] + [4] + {3} (one block) -- 8 cycles {5} (one block) -- 8 cycles [5] + [3 of 4] (one block) -- 8 cycles [remaining 1 of 4] + [4] + {3} (one block) -- 8 cycles This suggests that after the initial round, it will in fact only take 24 cycles per byte. Actually, it's more like this: [4],[4] (one block) -- 8 cycles {3} (one block) -- 8 cycles {5} + 3 of [5] (one block) -- 8 cycles [2] of [5] + [4] + [2] of [4] (one block) -- 8 cycles remaining [2] of [4] + {3} (one block) -- 8 cycles but that's effectively the same. If you go back to "each display-contended access takes exactly 8 cycles" then you have [4],[4] {3} -- 8 cycles {5} -- 8 cycles [5] or 29 cycles. So which is it? Is it RAM availability is in 8-cycle blocks or each RAM access takes exactly 8 cycles? Or is it worse than that? Please understand that I'm not trying to be awkward; I just don't comprehend the logic. Cheers! Geoff ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________