Re: Play games in a window or on a GFX card

From: Johan Klockars <>
Date: Wed, 29 Apr 1998 16:34:23 +0200 (MET DST)

> Hm, yes, this is a problem, though I don't quite understand how user
> applications can access first 32k of the memory. Some Super() and
> Supexec() equivalent is available perhaps?

The protection of low memory (it's not as much as 32k, but I can't remember
the correct figure) is done by external hardware on the ST, it's not
something the processor does. On the QL there's no such restriction and
it's absolutely necessary to have access from user mode to some of that area.

The only way to deal with it on a 68000 is to take care of the bus errors
that will occur on the ST...
The way I do it now is by 'fixing' the offending instructions and then
restarting them (yes, I know that "can't" be done in general ;-).
Another way would have been to rerun the instructions in supervisor+trace
mode, but since the ST wants some interrupt vectors in the same area, that
isn't possible.

> The question is if Mac applications can access these variables directly.
> If not, they don't have to be at the original place. If they can, some MMU
> stuff is really needed.

Dave Small apparently had to do something about this in Spectre, but I
don't think there's much point in making a modern Mac emulator run on less
than '030s in any case.

> MacOS itself causes copyright problems I guess. But it is avoidable. At

That's a problem with almost all emulators.

> Atari OS. It would be completely nice, if a Mac application could run in
> parallel with Atari applications under GEM. Well, to think about anything

ShapeShifter on the Amiga multitasks with the rest of the system and I
don't see why we wouldn't be able to have something similar.

Perhaps it's time for another attempt to contact Christian Bauer?
Surely there must be _someone_ who has time for a project like that!

> Thanks for the QL notes, without a knowledge of _ANY_ command I could
> only watch that white&red screen. Could you consider adding the same as


> you wrote in the previous mail (about QL) to the emulator documentation?

Yes, of course.
That will be rather boring, though, which is one of the main reasons why
I haven't got around to it.

There is some really good software available for QDOS (modern machines
have harddisks, Megabytes of memory, improved graphics and modern processors
(a really cheap '040 QL card for PCs was sold until recently)). My all time
favourite text editor for example, 'The Editor'. Even the bundled programs
(word processor, database, spreadsheet and business graphics) were really
good, IMO (and they're freely available on the net nowadays).

  Chalmers University   | Why are these |  e-mail:
     of Technology      |  .signatures  |  
                        | so hard to do |  WWW/ftp:
   Gothenburg, Sweden   |     well?     |            (MGIFv5, QLem, BAD MOOD)
Received on on. april 29 1998 - 17:15:00 CEST

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