From: shepperd@netcom.COM (David Shepperd)
Newsgroups: rec.games.video.arcade
Subject: Re: Do I have an Asteroids clone?
Date: 8 Feb 92 22:09:51 GMT


From article <7517@bnr-rsc.UUCP>, by smiller@bnr.ca (Scott Miller):
> P.S: I had asked about source code. Is there any way to buy/beg/borrow/steal
>      this, or do I get to dissassemble 8K of hand-coded 6502?  Since this is
>      ancient stuff, it couldn't be of anymore commercial value, or could it?

The bad news is: as a policy, we don't hand out source code to anyone without
a license agreement of some kind. I believe this policy holds even for
something as trivial as a link map (although there should be a memory map in
the manual).

The good news is: it's not quite 8k of 6502 code. I think Asteroids had a self
test/coin routine that was about 1k, and the program itself was about 3k. The
rest of the data in the EPROM was graphics for the VG. The VG was a 16 bit
processor and I seem to recall some vector commands (strokes) required 2
words. There were lots of strokes in the alpha-numerics. The VG and the 6502
shared portions of their address spaces (I think the VG could only address 4k
words). The 6502 had to build the VG commands in the shared memory then tell
the VG to go. I believe we used a double buffering scheme where we'd build the
next frame in 1/2 of the ram while the other half was being displayed. The VG
would always start at it's 0 location and we'd stick a JMP there to make it go
to the appropriate 1/2 of memory.

As was mentioned in a previous posting, screwing up the VG program would tend
to burn out the monitor.
-- 
Dave Shepperd.	    netcom!agc  or  shepperd@dms.uucp
Atari Games Corporation, 675 Sycamore Drive, Milpitas CA 95035.
Nobody knows what I'm saying. I don't even know what I'm saying.