Re: [hatari-devel] defaulting to SMALL_MEM

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On 13.2.2022 14.56, Nicolas Pomarède wrote:
Le 13/02/2022 à 11:46, Eero Tamminen a écrit :
Especially considering that non-existing ST-RAM areas can be *read* without exceptions, at least in some cases...

regarding non existing RAM, it all depends if you read RAM areas using the bank memory functions in stMemory.c that check for boundary (which is a little slower), or if you read memory by directly accessing the allocated memory, which can indeed go out of bound if all the proper check are not there (but is faster, which matters a lot when doing screen convert code)

There was recent discussion on EmuTOS devel list that non-existent RAM can be *read* without exception on *Atari* machines in certain cases. [1]

Thomas' change skips updating the internal video.c variables if (any part of) the current video line is past end of RAM.

While it's unlikely any program would intentionally rely on screen being mapped outside of existing RAM area temporarily, accidents can happen. And they might be relying on internal video variables being updated.

	- Eero

[1] David Henderson:

On my STE (stock processor with 4MB STRAM, no expansion) reads of the D00000 range don’t generate bus errors
NB. writing to that address *does* generate bus error.

Christian Zietz:

Yes, the STE has some additional unused ROM decodes, that allow reads from 0xD0xxxx.

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