19 February 2023, 02:36 | #1 |
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A4000 + 2MB Chip + 8MB Fast does not exist IRL
So I wanted to completely emulate an A4000 / 040 with MMU and FPU and PicassoIV on KS 3.1 40.70 and WB3.1 and found out that I am unable to start an A4000 with 2MB chip / 16MB 32Bit, I always have to add 8MB of Motherboard Fast Ram to get past this.
Weirdly enough, an A4000 never had 8MB of Motherboard Fast Ram, it had a jumper that was non-functional to activate it but it didn't actually have 8MB of Fastmem... |
19 February 2023, 03:03 | #2 |
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The 8Mb standard is the Zorro II buffer limit. Zorro III DMA is beyond that.
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19 February 2023, 09:11 | #3 | ||
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Quote:
Quote:
A4000 motherboard FastRAM is not mapped into the Zorro II address space. It has its own address space. $04000000 $07FFFFFF (64MB). With a GAL change to the A4000 motherboard you can fit 64MB of Motherboard RAM Zorro III DMA is a feature of some Zorro cards. I don't think you use the term DMA when describing the memory address space Last edited by alexh; 19 February 2023 at 09:29. |
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19 February 2023, 09:28 | #4 | |
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Quote:
IFAIK Z3 registers are beyond Z2 so yes DMA is probably the wrong word. |
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19 February 2023, 09:34 | #5 |
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Addresses not registers. And they are not next to one another. Z2 is in the middle and Z3 is right at the end
http://oscomp.hu/depot/amiga_memory_map.html |
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