Re: Asteroids DMACNT signal and vgen instruction set

Look at www.fpgaarcade.com / http://home.freeuk.com/fpgaarcade/ast_main.htm

He has built an asteroids deluxe pcb into an fpga.... he's a helpful chap
too....(based in UK)

Hope this helps,
Regards, Colin

----- Original Message -----
From: Philip Pemberton <philpem@dsl.pipex.com>
To: <vectorlist@vectorlist.org>
Sent: Sunday, December 11, 2005 12:19 AM
Subject: VECTOR: Asteroids DMACNT signal and vgen instruction set

> Hi,
> I'm currently reimplementing the Atari Digital Vector Generator in a
CPLD,
> reverse engineering it as I go. I've reverse-engineered the DVG down to
> microcode/state machine level, and have a documented instruction set
listing
> that covers everything except the "SVEC" instruction. I've even created a
> state transition diagram for the DVG state machine. No guarantees on
> accuracy, but I'm pretty sure it's correct.
>
> What I'd like to know is how the DMACNT signal is used. It appears to
have
> the same purpose as DMAGO (start the vector state machine running), and is
> generated as the result of reading from or writing to address $3800
(IIRC).
> Thing is, as near as I can tell, the Asteroids code never writes to 3800.
> What the heck is DMACNT there for, if it's never used?
>
> Also, does anyone happen to have any info on the programming aspect of
the
> DVG? I'm trying to figure out how the SVEC instruction is used, and how
its
> parameters affect the size of the vector. What I would really like to find
is
> a few example SVECs and the matching VCTR instructions.
>
> I'm also trying to find out if instruction $00 does cause the DVG to
halt
> (as has been suggested), or if there are certain instruction parameter
values
> that will cause similar effects. As usual, this sort of thing would be
easy
> to find out if I had an Asteroids PCB to play with, but I haven't seen one
> for sale in ages (well, not on this side of the 'Pond anyway).
>
> If anyone wants to take a look at my notes, drop me an email and I'll
send
> you the PDF. I don't want to release it too widely yet, because it's an
> incomplete work-in-progress and I don't want to see it all over the 'Net
> until I've at least had a chance to debug it.
>
> Thanks,
> --
> Phil. | Acorn RiscPC600 SA220 64MB+6GB
100baseT
> philpem@philpem.me.uk | Athlon64 3200+ A8VDeluxe R2
512MB+100GB
> http://www.philpem.me.uk/ | Panasonic CF-25 Mk.2 Toughbook
> ... Artificial Intelligence: The other guy's opinion.
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Received on Sat Dec 10 19:43:46 2005