On 26 April 2011 10:55, Chris Pile <chris.p...@blueyonder.co.uk> wrote:
> Mmmm, not sure I would have like hardware scrolling to be honest. It would > probably > have meant a glut of scrolling marioesque platform games. Which - for me - > is a whole > lot less desirable than infinite ball demos! > Yes, scrolling platformers become possible, as do scrolling shoot-em-ups (doing it in Mode 2 doesn't count), but it also means you can open up to innovative stuff like Thrust and Exile that would never have been possible on a 2MHz processor. You also get much more responsive text editors, basic editors etc. > Some sort of blitter to chuck large blocks of data around at high speed > would have been > a *very* nice addition. That 24k screen really is too much for the old Z80 > to cope with! > Eugh... _another_ thing to add to Simon's memory contention list? :) A blitter would have been costly both in terms of electronics and in terms of memory T-states. When I said "free" I meant it - a single OUT statement could set the memory start address and everything else would have stayed the same, with the extra port taking the ASIC equivalent of a couple of sets of gates. I guess the current screen address currently just gets reset to 0 every frame - but if you wanted to save the extra electronics required for a screen address register you could make it so the software had to reset it every frame interrupt. Actually that's silly, there wouldn't need to be any per-frame reset logic, just some logic so that when when bits 13 and 14 are both set they're both immediately cleared (0x6000 -> 0x0000) On 26 April 2011 10:54, Simon Owen <simon.o...@simcoupe.org> wrote: > Just those two could have made a huge difference to what was possible. > *sniffs* I do vaguely remember Simon Goodwin explaining why SAM missed out > on hardware scrolling, but I can't remember the details. I think it was > something RAM access related, so perhaps the change to use dedicated VRAM > would have made it easier? As a hardware n00b I've no real idea! Anyone? > I don't see how changing the start point within a 24k rolling window would make any difference to the RAM timing - you still have to access the same data the same number of times and at the same rate. My hardware experience is pretty limited though, so I'm not going to start contradicting Mr Goodwin. G
