New Agnus versions and game compatibility

[Supamax]

Hi mates,

let's suppose (for some reason) I took out my old 8371 Agnus from one of my A500s in order to fit a new 8372/8372A (1MB chip RAM support) or 8372B/8372AB (2MB chip RAM support), plus adding more chip RAM.

Would this affect game compatibility?
Would I be able to run those games which require no more than 512KB chip RAM? In other words, would I be able to temporarily disable the >512KB chip RAM, using some utility or hardware hack/switch?

EDIT: Let's suppose, too, that I have both chip and fast RAM expansion cards. If the aforementioned "chip RAM degrader" utility does exist, will it leave the fast RAM (and the slow/trapdoor RAM, if present) unchanged?

[zipper]

The degrader programs from Aminet do what you describe (TUDE, Degrader etc.) and more.

[Toni Wilen]

Extra chip RAM practically never causes any problems.

Missing slow RAM or ECS-Agnus only features that some games accidentally enable are the biggest problems and these can't be fixed by software.

EDIT: you can't have 1M chip (1M on mainboard) + trap door expansion simultaneously without extra hardware.

Software won't help (much) because most games use absolute addressing. (ok, it does help with some games, like system friendly games that are stupid and accept only fast ram..)

[Supamax]

Originally Posted by zipper

The degrader programs from Aminet do what you describe (TUDE, Degrader etc.) and more.

Thanks, I'll give'em a look .

Originally Posted by Toni Wilen

Extra chip RAM practically never causes any problems.

Do you remember those (fortunately not common) games which run on 512KB A500s but don't run if there's a slow RAM expansion present?
They required some nice utilities (or some custom bootblocks) which temporarily disabled the extra RAM.

I seemed to remember that something similar happened on A500s expanded to 1MB (or more) chip RAM... but perhaps I'm wrong.
Are there game titles which run on A500s (512KB chip) but don't run on A500+s (1MB chip)?

EDIT: you can't have 1M chip (1M on mainboard) + trap door expansion simultaneously without extra hardware.

Yes, of course .

[Toni Wilen]

Originally Posted by Supamax

Do you remember those (fortunately not common) games which run on 512KB A500s but don't run if there's a slow RAM expansion present?

These programs work just fine with 1M chip. Problem is non-chip RAM and badly coded programs putting graphics or audio data in fast ram instead of chip ram..

I seemem to remember that something similar happened on A500s expanded to 1MB (or more) chip RAM... but perhaps I'm wrong.

Other category of badly coded programs: requiring slow ram ("ram in 0xC00000? no -> NOT ENOUGH MEMORY PANIC!!11" even if total ram is 1M or more.. (1M chip or real fast ram)

[Supamax]

Thanks, Toni .
I think that all is clear to me, now.

EDIT: with reference to the other thread (Hardital Insider 2), if I swapped the old 8371 Agnus with a new one (and making the proper modifications on the motherboard, as written on my post) I could use the expansion at its full capacity, having a total of 2,5MB (1MB chip + 1.5MB slow).
As you wrote, I shouldn't have compatibility issues with games.

But... would my Action Replay v1.5 work? I don't think it supports 1MB chip RAM.