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MiSTer-devel / Minimig-AGA_MiSTer

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More Fast RAM Memory Options #110

Open SuperFrogFX opened 3 years ago

SuperFrogFX commented 3 years ago

More of a suggestion than issue - would it be possible to add 16MB, 32MB, 64MB and 128MB options for fast RAM? Currently there is jump from 8MB to 256MB. If I have to chose from those 4 options to add only one - then 16MB would be great. (there are different setup and most of turbo boards were between 8 and 32MB.)

sorgelig commented 3 years ago

There was an original 68000 RAM size cap due to 24bit of address which limited the total amount of addressable size to 16MB. And in these 16MB many areas were already occupied by ChipRAM and devices, so effectively it was possible to have ~10MB. That's why MiSTer's Minimig has 8MB expansion. It's simply compatible with 68000 mode. Once you switch to 68020, there is no such limit and it's up to available RAM. I don't remember any compatibility problem with 256MB. What compatibility problems you have? Otherwise there is no point to add useless options. Options there not "because i can", but because they have specific reason.

nretro commented 3 years ago

In a real Amiga, there are Zorro II (24 Bit) and Zorro III (32 Bit) address ranges. Zorro II looks like $000000-$200000 2MB ChipRAM $200000-$a00000 8MB Autoconfig space for memory mapped extensions (other than small (64K IO)) $c00000-$d80000 1.5 MB SlowRAM, the first 512K were very common in the early days and expected by some software. $e00000-$e80000 512KB ROM space when using 1MB ROMS $f00000-$f800000 512KB Debug ROM, not implemented in Mister but also only really useful in read hardware $f80000-$ffffff 512KB ROM This can all be configured in Minimig (with the exception of the debug ROM). Zorro III was only common very late in the life of the amiga, and is only used in the 3000 and 4000 models and in most accelerator cards. So there is no software that depends on a particular memory setup in Zorro III space. One option for "enable all we have" should work for all existing software.

sorgelig commented 3 years ago

if Debug ROM is actually implemented using HRTMON as debugger.

SuperFrogFX commented 3 years ago

I think you are right about memory for 68K - if I remember correctly (it's been around 30 years) A500 could get 8.5 MB (.5 chip and 8MB fast) and A500+ could get 9MB (1 + 8). I never said I had an compatibility issue, just suggestion to have 16 MB (or other memory options) if is not a big deal. Must be some sort of nostalgia as that is what I still have (A1200 with Apollo turbo card with 16MB EDO ram. )

axispod commented 2 years ago

Once you switch to 68020, there is no such limit and it's up to available RAM. I don't remember any compatibility problem with 256MB.

@sorgelig But standard MiSTer memory cards are 32MB or 128MB. So how will we use 256MB or 384MB?

sorgelig commented 2 years ago

DDR3 is used for FastRAM. SDRAM is used only for ChipRAM.

nretro commented 2 years ago

if Debug ROM is actually implemented using HRTMON as debugger.

HRTMON sits at 0xa10000 not in the Debug ROM range at 0xf00000. The Debug ROM area can be used to add additional ROM libraries and every Kickstart jumps to that area in the very beginning, if the right magic number is present at 0xf00000. That's quite useful in a real Amiga, but I haven't yet missed it in Minimig.