[MiNT] please help with Thing, blitter, VDI and FastRAM on TOS 4.04

[Petr Stehlik <joy@sophics.cz>]

Hi,

I added FastRAM to TOS 4.04 by calling Maddalt(0x100000, 0x200000). Then
started Thing from plain TOS (no TSR, no ACC). And Thing asks VDI to
blit some things _to_ FastRAM. Now if Blitter is connected with 23-bit
addresses only it must overwrite valid data in ST-RAM instead, is that
right? Does Thing have some reason to blit to FastRAM? Does it perhaps
allocate an offscreen buffer in the (fast)RAM?

What is the general solution in case of 23-bit Blitter and FastRAM? It
seems to me that VDI should copy all FastRAM data to ST-RAM first before
it allows Blitter to work on them (similarly to what you must do with
sound data). How is this solved in all those FastRAM expansion cards
(Afterburner, Centurbo, CT60)?

Petr