MdntTrain wrote:

>> 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?).
> 
> Well, I do for one.  And tubes.. and vinyl... :-)

Cool.  I grew up with audio and have it in my blood.  My late father, Julian 
Hirsch, was a well known audio reviewer and technical writer.  After years of 
striving for the utmost accuracy in analog reproduction, I think he would have 
found it somewhat upsetting to see devices using lossy compression (e.g. iPod, 
MP3 players, etc.) take over so much of the market.

I still have have about 400 vinyl LP records, although I've been chipping away 
at transcribing them to CD (48Khz. PCM, NOT MP3 thankyou-very-much).  I'm one 
of those folks who refuses to buy something twice just to have it on different 
media :-).

>> 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.

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
--- SBBSecho 2.12-Win32