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Old 27 November 2008, 10:28   #1
NovaCoder
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Use that 020...A1200 chipset questions

Just some random ramblings of a diseased mind....

Apparently the 020 is still warm/hot when using say an 030, does anyone know what the little fella is up to? This seems strange to me, I would have thought that plugging in an accelerator would disable the 020

Also, is it possible to still access the 020 in code and get it to perform some tasks (use it like a co-processor)? Has anyone actually done this in games/demos?

Finally am I right in assuming that as the AGA chipset's speed is set at 14mhz which is why you don't see any real improvement when plugging in an accelerator? For example it seems you are better using the accelerator to perform blitting @50mhz in code rather than using the chipset's blitter which is stuck in 14mhz land.

I don't suppose it's possible to 'overclock' the AGA chipset? I guess that would probably end in tears.

Thanks

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Old 27 November 2008, 11:07   #2
smoorke
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actually running dblpal or dblntsc doubles the chipset speed.
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Old 27 November 2008, 11:45   #3
Toni Wilen
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Quote:
actually running dblpal or dblntsc doubles the chipset speed.
No. It only doubles number of horizontal lines (and halves the length of lines) = 2xmore disk,audio etc.. dma slots but it does not increase speed, in reality it slows down because there is less slots for blitter and display..

Quote:
Apparently the 020 is still warm/hot when using say an 030, does anyone know what the little fella is up to? This seems strange to me, I would have thought that plugging in an accelerator would disable the 020
afaik only signal that means something like "bus in use" gets activated, 68020 is still active and waiting for bus cycles (that never arrive)

Quote:
Also, is it possible to still access the 020 in code and get it to perform some tasks (use it like a co-processor)? Has anyone actually done this in games/demos?
I'd guess there is not enough signals to handle multiple CPUs accessing same bus.

Quote:
Finally am I right in assuming that as the AGA chipset's speed is set at 14mhz which is why you don't see any real improvement when plugging in an accelerator? For example it seems you are better using the accelerator to perform blitting @50mhz in code rather than using the chipset's blitter which is stuck in 14mhz land.
Chipset speed is exact same is in OCS/ECS. (~3.5MHz DMA access rate, not 14MHz..) "Only" difference is 32/64-bit bitplane and sprite DMA support. (can fetch 32 or 64-bit in one cycle, instead of single 16-bit like in OCS/ECS)

Only way to make blitter "faster" in AGA is to always enable 64-bit bitplane mode (more DMA cycles available for blitter)

All other DMA channels, including blitter are still the same, 16-bit only. 32 or 64-bit blitter would have been really nice..

Quote:
I don't suppose it's possible to 'overclock' the AGA chipset? I guess that would probably end in tears.
It is possible but all chipset timings would also change..

Last edited by Toni Wilen; 27 November 2008 at 11:53.
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Old 27 November 2008, 12:31   #4
Thorham
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Originally Posted by Toni Wilen View Post
Only way to make blitter "faster" in AGA is to always enable 64-bit bitplane mode (more DMA cycles available for blitter)
How much faster are we talking about?
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Old 27 November 2008, 12:54   #5
Toni Wilen
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Originally Posted by Thorham View Post
How much faster are we talking about?
"depends"

Example 5 planes lores: (something that A500 can do)

OCS/ECS-mode cycle-diagram (16-bit)

Code:
84627351 84627351 84627351 84627351 84627351 ..
 x x xxx  x x xxx  x x xxx  x x xxx  x x xxx
AGA 64-bit cycle-diagram
Code:
84627351 84627351 84627351 84627351 84627351 ..
 x x xxx                             x x xxx
16-bit mode used cycles: 4x5 = 20 cycles, free cycles = 4x3 = 12
64-bit mode used cycles: 5, free cycles 8x3+(8-5)=27
= over 2x more free cycles left for blitter or copper.

BUT it isn't that nice.. Why use "low" color modes on AGA? More planes to copy = more blitter cycles to use = no gains in higher resolutions or color modes..
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Old 27 November 2008, 14:22   #6
Thorham
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Quote:
Originally Posted by Toni Wilen View Post
16-bit mode used cycles: 4x5 = 20 cycles, free cycles = 4x3 = 12
64-bit mode used cycles: 5, free cycles 8x3+(8-5)=27
= over 2x more free cycles left for blitter or copper.
So, does that mean copper intructions can execute in only four lowres pixels worth of time instead of the usual eight in low color modes? Would be nice to be able to set two 12bit colors per eight pixels
Quote:
Originally Posted by Toni Wilen View Post
BUT it isn't that nice.. Why use "low" color modes on AGA? More planes to copy = more blitter cycles to use = no gains in higher resolutions or color modes..
Hmm, but for games it's not always required to blit all planes all the time. Further more, having more blitter time means you can actually use more planes then normal anyway, could be good for multi-layer paralax scrolling (if I got it right)

Anyway, thanks for explaining
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Old 27 November 2008, 14:29   #7
Toni Wilen
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So, does that mean copper intructions can execute in only four lowres pixels worth of time instead of the usual eight in low color modes? Would be nice to be able to set two 12bit colors per eight pixels
No. Copper always uses odd (or even, I don't remember) cycles.
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