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PostPosted: Thu Jan 12, 2017 1:21 pm 
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Hi, i have a question, but i am not completely sure if i am posting this in the right place.

I found out that Akumajō Special: Boku Dracula-kun is using the Ines mapper 23, this is a mapper that is almost not supported, is there any "easy" way to change the mapper.
I am asking this because i want to play it on the NES mini and it is not supporting mapper 23.


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PostPosted: Thu Jan 12, 2017 1:49 pm 
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madmega wrote:
Hi, i have a question, but i am not completely sure if i am posting this in the right place.

I found out that Akumajō Special: Boku Dracula-kun is using the Ines mapper 23, this is a mapper that is almost not supported, is there any "easy" way to change the mapper.
I am asking this because i want to play it on the NES mini and it is not supporting mapper 23.

No.


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PostPosted: Thu Jan 12, 2017 1:51 pm 
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a difficult way then ?


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PostPosted: Thu Jan 12, 2017 2:23 pm 
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madmega wrote:
I am asking this because i want to play it on the NES mini and it is not supporting mapper 23.


How are you accessing the mini?


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PostPosted: Thu Jan 12, 2017 2:25 pm 
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with a USB cable


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PostPosted: Thu Jan 12, 2017 3:11 pm 
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madmega wrote:
a difficult way then ?

Sure: you reverse-engineer the entire game (to understand it, since it uses a VRC2/4 variant), then re-code the relevant parts to use a different mapper that's supported by the console.

If your next question is "how do I do that?" then considering your first question, the answer is: you don't. :) You might ask on the romhacking.net forum if someone is willing to try and convert said game to use MMC3 (mapper 4) or equivalent if possible. I would say 90-95% of the time this is not a "simple" task.


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PostPosted: Thu Jan 12, 2017 3:16 pm 
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madmega wrote:
a difficult way then ?

There are two difficult paths:

1. Disassemble the NES ROM and convert all use of VRC4 registers to a supported mapper, maybe MMC3?

2. Disassemble the NES mini software and add support for the VRC4 mapper.

I think the second approach is more useful, because if you can add one mapper to the software you can add them all. It would lay the foundation for getting all sorts of games on there. The first approach will only change that one game, and they're probably roughly equivalent amounts of work (though each requires experience with a different kind of system).


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PostPosted: Thu Jan 12, 2017 4:03 pm 
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I understand now, thank you.

No-one ever tried option 1 here on the forum, maybe a stupid question because than you would already stated as an option 3 ;-)


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PostPosted: Thu Jan 12, 2017 4:33 pm 
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Oh these Konami mappers...
They seem pretty difficult to hack.
AFAIK, Begalad did a Japanese Contra hack but give up on Gradius 2.
And he's a pretty experienced hacker!
When someone with his knowledge gives up this kind of project, I think the possibilities of a hack like this to suffice are very thin.
Does Nes mini supports MMC 5?
This could be a little easier to hack.
But I think the best option is the Rainwarrior's option 2, since this would open the path for many more games and many more mappers.


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PostPosted: Thu Jan 12, 2017 5:35 pm 
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Fisher wrote:
Does Nes mini supports MMC 5?

It does, but *how much* of MMC5 it supports (and if it's correct/proper) is unknown. Nintendo may have "done just enough" to make it play games provided on the device itself, rather than a full implementation. Again: nobody knows for sure as of this writing. I would really not recommend that mapper either (too complicated).

In general, MMC5 should not be chosen just because it's "the last/latest mapper Nintendo did"; that doesn't necessarily make it a feasible choice for conversions. With regards to the OPs inquiry, it really depends on what features of the VRC2/VRC4 Boku Dracula-kun uses (this requires RE'ing of the code and fully understanding it), followed by reviewing in depth each of the supported mappers by the device and then redesigning/reassembling the entire game to use said mapper. I imagine debugging/troubleshooting will be immensely painful (i.e. stick to using emulators first, then once you get something working, try it on actual hardware).


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PostPosted: Fri Jan 13, 2017 1:06 am 
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Thank you for your replies, i believe it is indeed the best option for someone, to hack the emulator of the NES mini


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PostPosted: Fri Jan 13, 2017 4:30 am 
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Fisher wrote:
AFAIK, Begalad did a Japanese Contra hack but give up on Gradius 2.

You are not mistaken. I gave up on mapper hacking Gradius 2 because
  • The game was randomly crashing for an unknown reason that I wasn't able to figure out (probably interrupt / IRQ related)
  • The IRQ scanline counter of MMC3 is incapable of working properly when sprites from both pattern tables are simultaneously used, and Gradius III does exactly that. Changing this is almost impossible, since the game was designed that way.
As a result I had at some point a playable, but glicthy Gradius 2 rom hack that would run on MMC3 and randomly crash on later levels when the game lagged too much. Since I saw no value in this hack I simply removed it.

Also, since the explosion of bootlegged cartriges that are sold for a high price on the internet, I also retracted my japanese Contra hack to MMC3.

I think trying to do Boku Drakula-kun on MMC3 would be difficult because you'd enter in smilar issues to those I encountered when hacing Gradius II to MMC3 - you could probably get a working version but it would have glitched graphics and might crash. Probably not something actually worth playing. Boku Dracula-kun also changes the mirroring mode very regularly in bizzare ways, and uses one-screen mirroring, which MMC3 does not support. Maybe TLSROM variant would be an option, but heh... is the effort really worth is, when you can just play the game on another emulator ?


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PostPosted: Fri Jan 13, 2017 5:37 am 
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Yes, but this is the Mini NES we are talking about, there is as we speak no option to alter the emulator.


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PostPosted: Fri Jan 13, 2017 1:27 pm 
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madmega wrote:
Yes, but this is the Mini NES we are talking about, there is as we speak no option to alter the emulator.

Then I guess if you're motivated it's worth trying to attempt mapper hacking BokuDracula-kun, as long as you don't expect to success. The first thing to do is to see where the game writes to its bankswitching registers, and replace it with bankswitching for the new mapper.


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PostPosted: Fri Jan 13, 2017 2:16 pm 
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I wouldn't even know where to begin hacking a compiled emulator, but I have the impression that hacking a modern program like that would be much harder than hacking a small 6502 program. Not that the latter sounds particularly fun either... Personally, I hardly see the "I wanna play game X on platform Y" situation as strong enough motivation for such extensive hacking, specially when there are other options for playing that are just as good (a Raspberry Pi in this case, maybe).


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