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"Dog version" of Virus dumped!
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hiroshi



Joined: 07 Oct 2004
Posts: 50

PostPosted: Wed Mar 27, 2013 4:05 am    Post subject: Reply with quote

Skrybe wrote:
Oh, nice! Gotta try this out on real hardware myself!

I just realized two player mode was not intended for use with FALL DOWN disabled, even on the earliest version of Virus. Sending pieces to the other player could instantly kill them.

There was an official Game Genie code to turn this off (I converted it for REV A owners):

GXXOZGVT + GZKPGZVT (RTM)
GXUOZGVT + GZSPGZVT (REV A)
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Skrybe
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Joined: 28 Aug 2003
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PostPosted: Thu Mar 28, 2013 1:02 am    Post subject: Reply with quote

Has anyone figured out what was changed between the two retail versions of Dr. Mario?
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KingMike



Joined: 04 Nov 2003
Posts: 898

PostPosted: Thu Mar 28, 2013 2:47 pm    Post subject: Reply with quote

I think it must be a bugfix of some kind.
CHR-ROM is identical, all changes are in PRG-ROM.
It would seem Nintendo inserted a total of $1A extra bytes into the code, pushing everything off.

(all address below are CPU addresses)
The RESET routine ($FF00) has an extra instruction STX $FE.
The NMI routine ($8005) has an extra instruction LDA $FE: STA $2001.

I'm not sure if there is a program that can detect data different entirely due to shifted code.

Whatever $FFF0 is, it was changed from $871C to $852D. Possibly some sort of header data, as it follows the text " DR. MARIO"

Extra data inserted at $FB03: $FD, at $FB0E: $F4CF, at $FB1C: $7ACF,
at $FBFE: $0881
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BMF54123
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Joined: 28 Aug 2003
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PostPosted: Thu Mar 28, 2013 10:09 pm    Post subject: Reply with quote

PRG1 was changed to apply PPUMASK settings (monochrome, sprite/BG visibility, color emphasis) during Vblank, instead of "whenever the game feels like it."

In PRG0, changes are stored to $FE, which is then copied to $2001 during Vblank, whereas PRG0 tends to just write directly to $2001 in the middle of a frame. (The game turns off the BG when paused to hide the playfield, which AS FAR AS I KNOW is the only time it changes PPUMASK.)

I'm not really sure why they made this change. Maybe some PPU revisions have issues with writing to $2001 mid-frame?

As for the data at $FFF0, it's probably just some sort of ROM identification information, along with maybe a checksum.
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KingMike



Joined: 04 Nov 2003
Posts: 898

PostPosted: Fri Mar 29, 2013 12:32 am    Post subject: Reply with quote

I remember now that Dr. Mario has some sort of anti-hacking feature that will crash the game once it enters the main game if some part of the title screen is edited. Though I can't remember if it's the text or the tiles. But I guess since the title screen isn't changed between the two versions, Nintendo wouldn't need to update it.
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Tongueman



Joined: 27 Feb 2004
Posts: 631
Location: Japan

PostPosted: Fri Mar 29, 2013 12:51 am    Post subject: Reply with quote

$FE is also the standard PPU $2001 storage location for the FDS BIOS and FDS games. Perhaps they originally thought of possible FDS conversion? Or perhaps a game like Knight Move uses the Virus engine? Just speculation.
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NESter



Joined: 08 May 2013
Posts: 7

PostPosted: Wed May 08, 2013 12:17 am    Post subject: Reply with quote

BMF54123 wrote:

[edit]
The sound engine is just a sped-up version of the one in Tetris. You can even poke $6F5 with a track number to play the original Tetris music!


This isn't present in the final game, is it? If it is, it'd be cool if there were a Game Genie code to try it on a real NES. But I guess something like that would have been discovered already.
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BMF54123
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PostPosted: Thu May 09, 2013 12:00 am    Post subject: Reply with quote

No, the Tetris music was removed from the final game.
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NESter



Joined: 08 May 2013
Posts: 7

PostPosted: Fri May 10, 2013 10:12 am    Post subject: Reply with quote

BMF54123 wrote:
No, the Tetris music was removed from the final game.


I thought so. Thanks.

I'm probably not to first person to notice this, but..

While playing around the prototype roms and comparing them with the final game, I noticed that in one of the Virus protos, I think the Playchoice 10 one, the victory music that plays when you clear a stage loops endlessly (and is a bit longer, I think) whereas in both the proto and final version of Dr. Mario it just ends abruptly. It seems to me like the music was meant to be looped but it somehow got glitched in the final revisions of the game and was never fixed.
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