Stellation Mill 6809 card clone / FPGA

[MdntTrain <js@cimmeri.com>]

{conversation moved from "Not your father's Applicard"}

Alex, Steven, I'd be very interested, and a committed buyer, for a
re-
creation of "The Mill" -- the 6809 board for the Apple II.   I don't
have one but here's a pic and little blurb on it:
http://www.vintagemacworld.com/8bit.html

What is the 6809 specific operating system claimed available for the
Apple II?!

~ JS

=====================
Steve Hirsh replies:

MdntTrain wrote:
> Alex, Steven, I'd be very interested, and a committed buyer, for a re-
> creation of "The Mill" -- the 6809 board for the Apple II.   I don't
> have one but here's a pic and little blurb on it:
> http://www.vintagemacworld.com/8bit.html

That would be more correctly: s/Alex, Steven/Alex/ :-).  He's the
man.  I'm a
software guy with enough digital hardware knowledge to be dangerous
(now,
analog audio systems are another story, but who uses them anymore?).

> What is the 6809 specific operating system claimed available for the
> Apple II?!

I'm guess it's Microware OS-9.  I've started working with that
environment on
my Tandy CoCo and it's a lot of fun.

Every once in a while a Stellation Mill will pop up on eBay, but they
always
go for ridiculous amounts.  The nice thing about Alex's upcoming FPGA
project
board is that you can implement the 6809 (or, better yet, 6309) in
synthesizable logic and have enough room left over for two or three
more CPUs.

There are FPGA designs for the 6809 out there already for the
picking.  The
real chips are getting difficult to find and the 6309 just about
impossible.
Not like the 6502 and Z80, I'm afraid.

Steve

=====================
David Wilson replies:

> What is the 6809 specific operating system claimed available for the
> Apple II?!

Yes - it was Microware OS-9 (I have that for my Mill card -
unfortunately it never worked on my IIe but did work on a II+ at
work...).

=====================
Steven H replies:

> Yes - it was Microware OS-9 (I have that for my Mill card -
> unfortunately it never worked on my IIe but did work on a II+ at
> work...).

Oh good.  Can you make the OS distribution available for posterity in
case
someone (me) wants to try cobbling up a 6809 on an FPGA?

=====================
JS replies:

> The nice thing about Alex's upcoming FPGA project
> board is that you can implement the 6809 (or, better yet, 6309) in
> synthesizable logic and have enough room left over for two or three more CPUs.

You mean YOU could implement it.   I wouldn't have the foggiest idea
of how to put a CPU core on an FPGA, much less the entire Mill card.
I'd like to learn, but man, what a stretch.  My brain is back at 7400
series.

How about this idea.   If Alex introduces his FPGA kit, what about a
group effort / learning project to recreate the Mill on his card?
All in the group would commit to purchasing Alex's card, then we'd
all
help each other learn about it and make kinda like an Open Source
project of getting a Mill, docs, and software all organized.   A
project like this would help legacy brains like mine learn about the
newer technologies.. it'd be a great thing that'd go beyond just a
Mill card... especially if enough people would get on board.


Course, I think it'd be even cooler to do a 68008 and CPM 68k, but
the
Mill -- if we can find the Apple II software for it -- is definitely
esoteric enough.


 JS

=====================
Steven H replies:

> You mean YOU could implement it.   I wouldn't have the foggiest idea
> of how to put a CPU core on an FPGA, much less the entire Mill card.
> I'd like to learn, but man, what a stretch.  My brain is back at 7400
> series.

Don't get me wrong!  I'm not anywhere NEAR far enough on the learning
curve to
code a CPU in VHDL.  But, I think sewing together modules written and
tested
by others isn't beyond my grasp.  I've been spending a lot of time
reading
through every book I can get my hands on, rewinding all the way back
to the
fundamentals of Karnaugh maps and by-hand logic minimization.  I
actually knew
this stuff reasonably well when I got my CS degree, but never worked
in the
hardware domain and it sort of dissipated.

> How about this idea.   If Alex introduces his FPGA kit, what about a
> group effort / learning project to recreate the Mill on his card?
> All in the group would commit to purchasing Alex's card, then we'd all
> help each other learn about it and make kinda like an Open Source
> project of getting a Mill, docs, and software all organized.   A
> project like this would help legacy brains like mine learn about the
> newer technologies.. it'd be a great thing that'd go beyond just a
> Mill card... especially if enough people would get on board.


I'm always up for a challenge, so why not?  The first order of
business is to
find some architectural information on the 6809 Mill.  The second is
to
reverse engineer the little piggy-back board that made it possible to
run OS-9
on the Apple.  If the implementation is anything like the CoCo (a good
bet),
memory re-mapping is a requirement.  Everything in OS-9 is fully
relocatable
and it dynamically maps logical <---> physical address space in 4k
chunks.  My
CoCo has 512K installed and it's able to use all of that by swapping
these
chunks into the 64k address space as needed by the currently running
task.
Task switching is triggered by a hardware timer interrupt.  Quite
sophisticated for a little machine.

The 6809 architecture is not really very similar to the 6502, and is
highly
optimized for relocatable, PC-relative addressing.

> Course, I think it'd be even cooler to do a 68008 and CPM 68k, but the
> Mill -- if we can find the Apple II software for it -- is definitely
> esoteric enough.

If your interests run in that direction, I believe there are designs
out there
for 68k cores also.

Steve

=====================
David W replies:

> I'm always up for a challenge, so why not?  The first order of business is to
> find some architectural information on the 6809 Mill.

Not a problem - the circuit diagram is published in the documentation
that came with it.


> The second is to
> reverse engineer the little piggy-back board that made it possible to run OS-9
> on the Apple.

No problem there either - I built my own to enable switching between
OS-9 and non-OS-9 modes via software instead of needing to take the
lid off and flick the little switch. The card is just a simple 4 bit
in 4 bit out to remap the upper bits of the address bus. Without the
board, the Mill has two address mappings:

0xxx..Fxxx => 0xxx.Fxxx (straight through)
0xxx..7xxx,8xxx..Fxxx => 8xxx..Fxxx,0xxx..7xxx (invert A15)

The daughter board remaps the 16 4KB banks in a similar fashion to
the
Z80 card giving OS-9 a larger contiguous address space than either of
the original mappings.


>  My
> CoCo has 512K installed and it's able to use all of that by swapping these
> chunks into the 64k address space as needed by the currently running task.
> Task switching is triggered by a hardware timer interrupt.  Quite
> sophisticated for a little machine.

The Mill OS-9 is only Level 1 so does not support more than 64KB. The
timer interrupt is not available on a standard Apple II so I think it
fakes it somehow.

=====================
Michael Mahon replies:

Of course, like all 68* machines, it's big-endian, so data exchange
with
a 65* machine is a bit of a pain...

-michael

=====================
Steve in Australia replies:

6809's and 6309 were very popular with apple clones towards the end
of
the Apple era. Many clones had all three processors - 6502, Z80 and
6809 on a single main board.

http://www.applelogic.org:88/AL/ACCORD.JPG

The adoptor I designed will allow as many processors you need to be
brought into an Apple II via peripheral cards, which includes
Hitachi's 63C09's and its hidden powerful instruction set.

http://www.applelogic.org/AL/6809+65C816hires.JPG

steve

=====================
JS replies:

> 6809's and 6309 were very popular with apple clones towards the end of
> the Apple era.

They were?  Why is that?

> http://www.applelogic.org:88/AL/ACCORD.JPG


** This link didn't work for me.

> The adoptor I designed will allow as many processors you need to be
> brought into an Apple II via peripheral cards, which includes
> Hitachi's 63C09's and its hidden powerful instruction set.

> http://www.applelogic.org/AL/6809+65C816hires.JPG

Steve, what the heck is this a picture of??   And tell us more about
this "adoptor"?

JS

=====================
A2Retro replies:

> ** This link didn't work for me.

Remove the port number 88 from the url

=====================
David W replies:

> Is the Mill similar to the PCPI card in that it's a full computer
> running with the Apple II as a terminal host?    What would the Mill
> have been typically purchased for?


No, it is closer to a Microsoft Soft Card - no on-board RAM. The 6502
only gets to run during 6809 dead cycles.

The Mill was available in 3 software configurations.


1) 6809 Assembler - runs under DOS 3.3
2) OS-9
3) Apple Pascal Speed Up - offloads math computations to the 6809
(not
sure as I never had this one).

=====================
Alex Freed replies:

> Hehe.. well, likely the first is to wait for Alex to be on board with
> all this.. as without his projects, it's a no-go.



The upcoming Carte Blanche will be a perfect platform to implement
it. There are too many Apple related projects in my pipeline that I
doubt I'll want to make a special project for it.
I've *heared* that 6809 was a wonderful CPU but never used it in
any form.

There exists an FPGA implementation of a 6809 system easy to port
to any FPGA. Some years ago I did build it for an old Spartan 3
board from Digilent ($99) but didn't know what to do with it :)


If someone posts a pointer to the board schematics I'll tell you
how easy it will be to clone.


-Alex.

=====================
JS replies:

JS send schematics to Alex.