It was recently pointed out to me that Clay Cowgill produces a kit (among
many fine others) for a Tempest multigame. In that kit was a custom game
written by Clay himself, "Vector Breakout", which works on the Tempest
hardware. You can visit his page here:

http://www.multigame.com/tempest.html

Understandably, Clay is a very busy person, and we really can't expect a
brain dump from him. But I managed to get the details from him regarding
the use of MAME for programming the Tempest hardware. [My comments will be
in these brackets.]

> Did you use MAME to develop your vector breakout? If so, any comments
> on the experience that you can relate?

Yep, I used MAME.  My comments on MAME?... "Don't trust MAME." ;-)

Seriously though, all the information I needed to program on Tempest
Hardware I basically got from the MAME sourcecode on Tempest, Jess Askey's
AVG description, and my old "Mapping the Atari" book for info on POKEY. 
(Jess' description doesn't document everything apparently. There's some
kind of subroutine call that I don't understand that isn't listed.  It's
implemented in MAME, so digging through the source there might be enough
to figure it out-- I just ignored it...) 

MAME beats the hell out of burning ROMs, but it has some shortcomings:

a) No concept of vector drawing time-- images (no matter how complex) 
always draw in MAME.  The real game has a finite amount of time to finish
before flicker becomes a problem.

b) Monitor behaviour-- real code must appease the [vector] monitor or else
objects won't position correctly and/or the spot killer will get you. [The
spot killer will turn "off" the monitor if there isn't enough positional
movement of the gun across the screen.]

c) POKEY-- MAME doesn't really model the behavior of POKEY's I/O ports
correctly.

d) IRQ's-- MAME doesn't handle IRQ's correctly.  (You can write code
that runs on MAME but will hang a real machine quite easily.)

e) VRAM-- MAME doesn't handle VRAM accesses (in particular bus contention)
properly/at all.  (You can always access VRAM in MAME, not so on real
hardware.) 

f) Long vectors-- MAME does something funky with some types of long vector
draws.  It'll look "fine" on the MAME screen, but be goofy on the real
hardware.  I think MAME can interpret the most significant as a sign-bit
in some instances... Since I switched to a little vector-editor of my own
the problem basically disappeared.  Go figure. 

g) Vector Generator-- MAME allows vector generator features that aren't
on the real hardware. ("Sparkle", for example.) [The MAME code for the
Atari Vector Generator is not just used for Tempest, but Major Havoc as
well. It's going to have additional features that aren't really there in
the real thing.]

Once you work around the above though, things work reasonably well and
it's a boatload faster than any alternatives.  Plus, just being able to
single-step and set breakpoints is worth any/all hassles. [Not to mention
setting up real-time memory monitors on the screen.]

I wrote Vector Breakout in a few weeks of off and on work.  The Menu
System in something less than 1 week...

I like your idea to document the Tempest source-- I'd help but I'm busy
on a multitude of other projects...

-Clay

P.S.  I reported the above stuff to the MAME team for fixing back in
April?  So some of might be better now...