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Old 05 November 2016, 11:37   #90
meynaf
68k wisdom
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Join Date: Nov 2007
Location: Lyon (France)
Age: 44
Posts: 2,379
Quote:
Originally Posted by roondar View Post
I'm not too sure the 68000 is 2x as fast - movem writes or reads one word per 4 CPU cycles/long word per 8 cycles (plus between 8 and 14 cycles overhead per movem). If you count the reading as well as the writing, using it should take the same time as using the copper.
While some of this work can be performed during the horizontal blank (setting first color bank, preloading second), the 68000 is indeed probably not fast enough to do better than the copper.


Quote:
Originally Posted by roondar View Post
Of course. But that doesn't change that there are also accomplished Amiga developers who had no exposure to the Atari ST.

My point isn't to say that Atari ST developers are not good (in any way!), my point is that there are great Amiga developers as well. And personally, I don't feel that the chipset advantages mean you can really afford to be lazy. A bad piece of code on the Amiga will also create a bad result - blitter/copper or no.
We certainly agree on this.

Personnally I've found the Amiga to be more difficult to code on, but more rewarding, than the Atari.


Quote:
Originally Posted by Thorham View Post
Whether or not the CPU is faster than the copper doesn't really matter because of the limited chipset register bandwidth. I've written the color registers with a 50mhz 68030, and you're still limited to one color per 8 lowres pixels.
Are you sure it's 8 lowres and not 4 ?
A 50mhz 68030 can access chipmem every 28 clocks or so. That's around 1.7 Mhz, i.e. 4 lowres, 8 hires, 16 shres pixels.
This assumes, of course, that the cycles aren't used by anything else (like extra bitplanes).
If the limit is one color per 8 lowres pix, then the assumption that chipmem and chipset have same timing becomes wrong...
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