A4000 + 2MB Chip + 8MB Fast does not exist IRL

mstreurman · 19 February 2023, 02:36

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...

Snoopy1234 · 19 February 2023, 03:03

The 8Mb standard is the Zorro II buffer limit. Zorro III DMA is beyond that.

alexh · 19 February 2023, 09:11

Quote:

Originally Posted by mstreurman

Weirdly enough, an A4000 never had 8MB of Motherboard Fast Ram

I'm 99% sure that was a valid configuration it was sold with. 4MB, 8MB, 16MB of Motherboard FastRAM

Quote:

Originally Posted by mstreurman

it had a jumper that was non-functional to activate it but it didn't actually have 8MB of Fastmem...

That was ChipRAM

Quote:

Originally Posted by Snoopy1234

The 8Mb standard is the Zorro II limit.

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

Quote:

Originally Posted by Snoopy1234

Zorro III DMA is beyond that. Zorro III DMA is beyond that.

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

Snoopy1234 · 19 February 2023, 09:28

Quote:

Originally Posted by alexh

A4000 motherboard RAM is not mapped into the Zorro II address space. It has its own address space.

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

It's confusing motherboard and fast ram in one sentence.
IFAIK Z3 registers are beyond Z2 so yes DMA is probably the wrong word.

alexh · 19 February 2023, 09:34

Quote:

Originally Posted by Snoopy1234

IFAIK Z3 registers are beyond Z2

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

19 February 2023, 02:36	#1
mstreurman Registered User Join Date: Mar 2021 Location: Criatia Posts: 4	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...

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19 February 2023, 03:03	#2
Snoopy1234 Registered User Join Date: Apr 2022 Location: Australia Age: 52 Posts: 902	The 8Mb standard is the Zorro II buffer limit. Zorro III DMA is beyond that.

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