[Coco] CoCo Game Master Cartridge developer offer

John W. Linville linville at tuxdriver.com
Fri Oct 20 17:19:46 EDT 2017

I'm not exactly sure when the great race for CoCo audio supremacy
began. I remember ruminating about the possibilities of adding audio
to a CoCo cart for at least a couple of years now, maybe more. It's
odd, it seems like not too long ago when just the idea of a basic
ROM cart for the CoCo seemed out of reach...

Anyway, somewhere along the way (especially after I demo'ed some
audio tech for CoCoFEST!) the idea caught on and suddenly everyone
wanted enhanced sound on their CoCo.  The main problem being, everyone
wanted their own version of a solution. Some of those ideas were odd
or questionable from the beginning, others had some legs but lacked
obvious purpose, while others remained plausible but with limitations
due to their own designs. In short, some of the proposed CoCo audio
solutions were more "sound" than others.

Earlier this week, one of the stronger contenders became available
"for experimenters and assembly language programmers who would like
to work with digital sound on the CoCo". The backer of that project,
Ed Snider, knows that software for new hardware can present a "chicken
and egg" problem. His design is a more susceptible to that problem
than some other designs, since it is more elaborate and probably not
appropriate for shipping a copy of the audio hardware on cartridge
with every game that supports it.  Nevertheless, even if a certain
design enables a game cartridge to economically ship with its own audio
hardware (removing the need to acquire the hardware in advance), there
are those that will insist on having such hardware before committing
to develop uses for it. The availability of the Game Master Cartridge
design in MAME alleviates this desire for some potential developers,
but apparently not for all.

So with that in mind, I am hereby offering an opportunity for folks
to acquire their own Game Master Cartridge hardware by pre-ordering
through me. A pre-order is merited based on the fact that I had never
intended to offer the Game Master Cartridge as an independent product,
but instead as a finished product shipping with a release game. So,
consider this as an offer for developers and other technical-minded
folks that are looking to experiment with the SN76489 on the Tandy
Color Computer.

I am offering the following options:

	Bare PCB		 7.00

	PCB + parts kit		12.00
	(ROM socket, no ROM or EPROM)

	Assembled card		20.00
	(ROM socket, no ROM or EPROM)

	Assembled cartridge	30.00
	(ROM socket, "P-Touch" label)

If you wish to acquire one of the options offered above, please contact
me ASAP via email to "linville at tuxdriver.com" with a subject of "CoCo
GMC developer offer". Iff and when I acknowledge your email, you may
then pay for the item in question via Paypal to my email address. Do
not pay me unless and until I have explicitly accepted your inquiry, as
I may not have the capacity to handle every request in a timely basis.

Along with the SN76489 audio hardware, this cartridge includes ROM
"bank switching" hardware that is compatible with what was used for
Predator and Robocop. The bank switching hardware portion of the
design is documented in "Breaking the 32K Barrier" by Greg Zumwalt,
The Rainbow, June 1990. The bank switch register is addressed at $ff40.

The SN76489 audio hardware is addressed at $ff41. It is clocked
at 4 Mhz by an onboard oscillator. The oscillator speed value
could be changed for those determined to play very low notes
(e.g. octaves 0 and 1), but is sufficient for a wide variety of musical
entertainment. Tools exist for working with this chip on a variety
of other retro platforms, and some are beginning to be available for
the CoCo as well.

Since this hardware design was designed to be used as a ROM cartridge,
the address decoding makes use of the SCS! signal. This causes the card
to conflict with most (or all) floppy drive controllers, the CoCoSDC,
and probably some other hardware. These devices can coexist in the
same machine through use of the Multi-Pak Interface and its ability to
multiplex the SCS! line. I understand this limitation to be in common
with some of the other existing CoCo audio designs, including CoCoPSG.

A good option for using this cartridge might be as an HDB-DOS ROM
cartridge for using Drivewire. A small modification will need to be
made to the PCB to enable use with "DOS-style" ROMs, which I will
be happy to document. Such usage might be especially attractive
to software developers, since that would allow access to DSK image
from both the CoCo and a more modern development host acting as the
Drivewire server.

There is no specific limit on the number of cards/carts/kits
available. However, I reserve the right to withdraw this offer at
any time due to exhaustion, lack of interest, any other reason,
or no reason at all. Notice of such withdrawal may or may _not_
be given publicly or in advance. YMMV... ;-)


John W. Linville		Someday the world will need a hero, and you
linville at tuxdriver.com			might be all we have.  Be ready.

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