Originally Posted by Samurai_Crow (Post 1130184)

Going from ECS to AGA is straightforward. Audio and blitter didn't change between them. All AGA adds is big sprites, more palette registers, fast Copper when the display is inactive, color bank switching for sprites and dual playfield mode, faster video fetching, and guaranteed access to Kickstart version 3.

Originally Posted by sandruzzo (Post 1130298)

Fast Copper?? How?

Originally Posted by Samurai_Crow (Post 1130314)

Two steps: 1) enable the control bit in the appropriate register, 2) disable the display DMA so the Copper can take over its bandwidth. The fast Copper is why Copper chunky is 4 times the horizontal resolution of ECS Copper plasma.

Originally Posted by chb (Post 1130334)

I'm actually quite sure that copper speed did not change in AGA... the increased horizontal resolution for chunky plasma comes from the fact that due to the 256 color regs you can "buffer" the writes during two scanlines. But you can't have more than 57 color register writes* per scanline, both on OCS and AGA.

* using the copper, that is... but I've never seen a copper chunky effect using the cpu to write to the color regs.

Originally Posted by Samurai_Crow (Post 1130337)

When doing 12 bit color on an AGA Copper chunky screen you are using the same circuit that allows the 2 bank switch commands between the even bits and odd bits for the color register writes. If the Copper were the same speed as ECS it would take about 6 rows of pixels to update a 256 entry of true color palette entries.

Originally Posted by Samurai_Crow (Post 1130337)

If the Copper were the same speed as ECS it would take about 6 rows of pixels to update a 256 entry of true color palette entries.

Originally Posted by Spec-Chum (Post 1130335)

Another quick question, although I suspect the answer is subjective.

Both the "HowToCode7" guide and "Mapping the Amiga" book state (paraphrase) "Do NOT poke registers on AGA, use the OS routines". The HTC7 guide even goes so far as to say code using OS will be 20 times (?) faster due to no wait-states in the ROM code.

So, if I intend to code an (albeit simple) AGA demo, should I do it "by the book" with OS calls or "hit the metal"?

I'll be using asm if that makes any difference, but I am competent in C too...

Originally Posted by chb (Post 1130341)

Well, there were mainly two reasons for using the OS on AGA:


1) Contrary to ECS, Commodore never officially documented the chipset, so they could change all AGA registers in any new revision (and probably would have done so). As there will be no new Amiga chipsets, that reason is not valid anymore.
2) If chipram bandwidth is low, ROM functions are indeed faster, but if your screenmode leaves enough room for the cpu (and on AGA that's at lower resolutions mostly the case) that argument is also void.


So, I'd say it comes down to your personal preferences.

Originally Posted by chb (Post 1130340)

I don't fully understand what you are saying... on AGA,color bank and upper/lower bits are selected by writing to bplcon3. I do not see how this can speed up the copper writes?

On AGA you get approx. 57 color changes per line (a bit less, because you need to write to bplcon3 also), so you can e.g. change ~110 colors in two scanlines, giving you a 3x2 copper chunky. I've never seen something better than fullscreen 3x2 copper chunky, could you give an example of such an effect or game?

On OCS, using 4bpl mode and sprites, you could do 4x1 with ~55 or so pixels per line. Less usefull indeed, but that's not because of the copper speed - you just have less color registers.



Yes, and it indeed takes that long. Until I'm completely mistaken, copper is the same on OCS and AGA.

EDIT: Tony beat me.

Originally Posted by Samurai_Crow (Post 1130768)

The Copper doesn't go faster when the display DMA is active. It is a reallocation of bitplane DMA that allows it to update the screen registers in 2 rows of pixels between Intuition screens.

Originally Posted by chb (Post 1130771)

Do you have any documentation or examples on this? I highly doubt copper is any different on AGA, as Toni Willen said, there were no updates. Updating all 256 color registers in 24 bit needs 528 copper moves (512 upper/lower color regs + 16 x BPLCON3), that's just impossible to do in 2 lines even if copper could use all memory cycles, including the even ones (which it cannot). You'd need some FMODE-burst thing for the copper, which isn't there.

As said, I'd be highly interested if you'd prove me wrong, because this would open a lot of new possibilities, but I've never seen any hint that something like you describes exists.

Originally Posted by Samurai_Crow (Post 1130780)

It appears I cannot confirm it from any sources on the Web including AGA Guide. When I last discussed it was at an Amiga DevCon in 1998 in St. Louis, Missouri. That may have been discussion of future chipset possibilities (that were ultimately rejected by Amiga Inc.). :(

Originally Posted by sandruzzo (Post 1130807)

With Aga we have more cycles per line, not faster copper, so we can have more instructions per line.