New Tempest code hacking

Since the Tempest code project has been sitting on my servers for some
time, I get sporadic e-mails from people about it (even though, yeah,
I'm just hosting the files).

Anyway, I recently received some e-mails from a gentleman who has been
digging about in the code. He's produced a 'new' annotated disassembly
of the game code - although he is not done with it.

For anyone that is interested, here is a link to the most current
commented code. He suggested it will get updated somewhat frequently.
http://216.46.5.1:18804/

BTW, I don't think his debugger is very portable, so you probably
shouldn't even ask for it ;) However, he suggested that if you would
like to contact him and discuss the Tempest code, please do so. His
e-mail address is: mouse@Rodents.Montreal.QC.CA

Here are some of his comments and some cool bits of Tempest code.
--------------------

"In particular, I wrote a highly flexible disassembler that makes a very

useful tool for this sort of "disassemble and uncompile" work.

I do not actually own a unit yet :-(, so I'm playing with the [XMAME]
engine, severely hacked to display over my house LAN to a SPARC
display, with the spinner input taken through a somewhat arcane
protocol from the parallel port (I have a real knob I built interface
circuitry for).

...As I designed the
remote-display protocol, it is driven off the vector display lists.
Rather than extend it to carry rasters as well, I just made my
interface do displaying by creating its own display lists. Rather than
design my own vector font, I used the one that was already there. (To
the extent that I could; I had to design a few more characters.)

...I've hacked on my MAME emulator so
that it now has some fairly nice dynamic debugging capabilities in it.
I have a program to take screenshots off a cg6, which is what I'm using
to display it; two screenshots

[ I've mirrored them here:
http://www.ionpool.net/arcade/tempest_code_project/tempest_debugger1.gif

http://www.ionpool.net/arcade/tempest_code_project/tempest_debugger2.gif]

The former shows the debugger interface, the
latter the game running with some watches set. This allows me to do
things like set breakpoints (the red address in the code listing at the
right of the debugger snapshot indicates a breakpoint), single-step,
patch RAM values or CPU registers, that sort of thing.

...Eventually I'd like to uncompile Tempest far enough to
extract the algorithms and reimplement it in pure C, so I can ditch the
MAME emulator engine.

Here's a rough summary of the more interesting things I've found so far:

- At 9181 and following is some code is some code which looks as though
  it's the code run to start a new level during attract mode.

- At 91b5 is code to load the starting-level bonus into $29/$2a/$2b.
  It uses the table starting at 91c6; the table is the bonuses in BCD
  with the low 00 not stored (that comes from the lda at 91b7).

- I've managed to deduce some of the layout of the table that runs from
  9607 through 9676 and related stuff.

- aaf5 is a routine that takes a number in A in binary and converts it
  to two-digit BCD, which is left in A, $29, and $2c. It keeps only
  the low two digits.

- c98c appears to be a routine called to go up a level.

- The 8 bytes from caf1 through caf8 appear to be the low two digits of
  the score values of something (speculation: various enemies). The 8
  bytes from caf9 through cb00 appear to be the high two digits ditto.

- df09 appends a video RTS, and df10 a video HALT, to the video list
  being built.

- df19 appends a video JSR appropriate to the digit in the low four
  bits of A; if the C bit is set, zeros turn into spaces, and the C bit
  is cleared if the digit is nonzero.

- df53 appends a zero-length line to the video list being built.

- df5f increments the video list pointer according to how much stuff
  has been appended.

- dfb1 appends a multidigit number to the video list being built; Y
  holds the length of the number, in two-digit pairs, and A holds the
  zero-page address of the lowest two digits."

-----------------------

tm

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Received on Wed Apr 9 10:10:54 2003