Re: [hatari-devel] defaulting to SMALL_MEM

[Thomas Huth <th.huth@xxxxxxxxx>]

Am Sun, 13 Feb 2022 19:10:44 +0200
schrieb Eero Tamminen <oak@xxxxxxxxxxxxxx>:

> I.e. if screen pointer would be in such RAM area, should the other
> video related counters still change or not?

Well, likely yes, but in this case I wonder if that'd buy us much. It
certainly would make the current ST-low rendering code (which is
already quite complex) way more complicated (and likely slower) if we
add checks there all over the place. And for what? As long as we don't
know of any program that relies on such weird behavior, it does not
have any benefit for us, does it?

> And should there be any additional exceptions happening if screen 
> pointer is set to non-existing RAM?

I don't think so. Apart from the CPU, none of the other chips can
trigger a bus error, as far as I know.

> And does that behavior differ between different Atari machines and 
> memory addresses?

As we recently learnt, the SCSI DMA controller in the TT can at least
detect bus errors and signal that via a bit. But I don't think that
this will trigger a normal bus error exception on the CPU.

 Thomas