Re: Working, slowly, on a BASIC.SYSTEM clone of sorts

["Michael J. Mahon" <mjmahon@aol.com>]

Lyrical Nanoha wrote:
> On Sun, 4 Dec 2005, Eric Smith wrote:
>
> > "Michael J. Mahon" <mjmahon@aol.com> writes:
> >
> > > Any program that calls DOS directly is going to pose some serious
> > > difficulties in any case.
> >
> >
> > It should be possible to write code to emulate the DOS file manager
> > calls.  That might help some DOS programs run on ProDOS.

Absolutely.  I wonder what fraction?

> That sounds about right.  I think what it really comes down to, is, how 
> to take DOS 3.3, yank out the File Manager and init code, and change it 
> into ProDOS calls, make sure the $BFxx page is clear, and write a 
> relocator (the last part is the easiest, lol).  I think, if I had a 
> complete DOS 3.3 disassembly, ready to build with CC65's assembler, it 
> wouldn't be very hard even for me.

My concern would be about the split between programs that "call"
DOS by using the CTL-D escape, vs. programs that call the file
manager _only_, vs. programs that call (or PEEK) at non-standard,
non-documented places.

If 90% of DOS programs work with CTL-D implemented, and 9% more
work with file manager entry points, then that's great.  On the
other hand, if a sizeable fraction of the 10% (say) that don't
work with CTL-D use more than the file manager entry points, then
the payoff for implementing the file manager interface is not so
good.

It would be great to have some data on just what compatibility
interfaces are required to achieve X% compatibility.

My recommendation would be to implement the easy part first,
then see what doesn't run, and why.  It may be easy to get the
first 90%, but it is almost certainly quite difficult to get
the last Y%.

Since direct calls to DOS were so poorly documented and never
really intended for use, those who did use them were pretty
much on their own, and may have done "whatever worked", which
makes compatibility a chore.

-michael

Music synthesis for 8-bit Apple II's!
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