ProDOS-86, yet another stupid Apple ][-related idea that will probably go nowhere

[Steve Nickolas]

Several years ago, I thought of the idea of implementing ProDOS on some
machine other than an Apple ][. I know it's stupid, insane and useless,
but I decided to make ProDOS on an XT a thing, after some experience with
my Tandy 1000HX about 20 years ago.

Currently, I'm still at a complete loss of direction, but I did manage to
write an IPL for it, i.e., a bootloader that can load a kernel file off a
disk. Of course, it's NASM code for an 8086. I haven't even tried to
make a "diglot" boot sector the way I do on an Apple ///.

http://6.buric.co/p86head.a86.txt

-uso.

[qkumba]

The interleave exists to avoid the "TXA / ASL / TAX" thing for doubling an index.
You don't need the "add di, 0x100 / sub di, 0x00ff" stuff. You can "mov ah, [cs:di+0x100] / inc di".

[Steve Nickolas]

On Thu, 14 Oct 2021, qkumba wrote:

> The interleave exists to avoid the "TXA / ASL / TAX" thing for doubling an index.
> You don't need the "add di, 0x100 / sub di, 0x00ff" stuff. You can "mov ah, [cs:di+0x100] / inc di".
>

You can tell I don't speak fluent x86. This is definitely a 6502-flavored
8086 ASM, for the most part.

The next thing I need to do is figure out the "device issue" in a way that
makes it look like an Apple ][ (e.g., A: as device 6).

By making some tweaks to the floppy bootloader I went from being able to
load about 32K (which is probably more than enough, given the size of
ProDOS-8 2.0.3) to theoretically being able to load 128K, which would
almost be big enough to run the later versions of MS-DOS. Better safe
than sorry...

-uso.