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Old 02 October 2019, 23:26   #1
sandruzzo
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A500: why they didn't do it?

I was thinking about how enhance a little bit A500 without upping the price.

1 Since HW registers are ram: why don't put them outside bitplanes' dma slots?

2 Put trap door ram outside bitplanes' dma slots, and give to copper and blitter the ability to access to it. So copper could run at full speed allways.

3. Optional 4kb of ram for stack pointer.

I think, even back in the day, whe they were there design Amiga HW, would had cost nothig to do so.

Think about how much faster could have been, with this simple changes!

Alex
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Old 02 October 2019, 23:56   #2
NorthWay
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1. Because they are part of the chips and they follow the chip timings. Values have to propagate through and between the chips and they are read and distributed during the available timing slots.

2. Trap door ram was _cheap_ because Agnus did all the refresh logic for you already. It's just an extension to a chip without enough pins to address it.
The copper is clocked by the chipset anyway and is routed through the internal bus of which there is only one and as I said it can only use the available timing slots.
You can find non-chipset Ranger ram in A1000 addons, but those were more expensive...
(What you should have asked for is a burst/rept mode for the copper, where you just point it at the first register and then it reads N words from memory and places them in the subsequent registers. Like 68K autoincrement address mode.)
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