[Coco] TC-9

[Chuck Youse]

On Mon, 2008-07-07 at 13:22 -0500, Joel Ewy wrote:
> Chuck Youse wrote:
> It uses a GIME, some TTL chips, and the DAT board from a Disto 1M
> upgrade.  A cursory glance reveals no PALs or GALs.

I have some 74S189s (16x4 static RAMs) that, in pairs, would make for a
very GIME-like MMU (with 2MB of addressable space), minus the FExx
fixed-page and always-map-FFEx-to-ROM features.

My concern about designing such a system is the amount of modification
that would be required to NitrOS-9 - in Level II in particular, the
NitrOS team have made a lot of assumptions about the hardware platform
and these references aren't really localized to one specific place.
This isn't a criticism, their aim was "make it fast on a CoCo 3", a goal
they've consistently met admirably, but that necessarily means a
sacrifice of portability.

It almost seems more straightforward to take NitrOS-9 Level 1 and port
it to the 68000.  I wonder if Radisys would take note of that project
and get itchy as it could conceivably compete with their (still-current)
OS9/68000 product, though it would probably differ in some significant
ways.

With a 68008 @ 8MHz, there would be a noticeable (but not extravagant)
increase in speed.  There's no complexity associated with a DAT or the
ugliness that that introduced to Level II.  The upgrade path to a 16MHz
68000 (still available, mind you) is largely brainless, and that
provides 16MB+ of memory space.  All of this while still maintaining a
_very_ hackable system for good fun.

> >   
> I also have a couple of Motorola 6809 (not 6809E) EXORBUS boards, which
> are essentially SBCs that can be plugged into a bus to hook up to other
> stuff.  I haven't done much with them yet, but I have looked into what
> it would take to run OS-9 from ROMs.  They have a bunch of sockets that
> can be jumpered to accept (EP)ROMs of various capacities or SRAM chips. 
> No MMU or DRAM controller, but those things could be added on an
> external board.  I do have full schematics for these boards in the
> Motorola docs.  I told somebody on this list (Willard Goosey?) that I
> would scan the docs sometime.  I haven't done it yet, but haven't
> forgotten either.  So maybe it's time to do a bunch of scanning...

A basic 6809 system is rather easy to construct - a non-DAT system with
64K of RAM to run Level-1 would be a one-day project, assuming you have
the parts.  Might be more trouble than it's worth to try to use those
EXORBUS boards, who knows.

C.