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PostPosted: Mon Jun 14, 2010 8:46 am 
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Joined: Wed Nov 29, 2006 10:11 am
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Location: Trieste, Italy
can anyone shed some light on the Sunsoft "Double Cassette System"?

Is there any info available in addition to NEStopia source?

what are the difference between this and plain Sunsoft-4/NTBROM?

which games use this? (Nantettatte Baseball?)

thanks in advance


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PostPosted: Mon Jun 14, 2010 7:35 pm 
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Joined: Wed Jul 13, 2005 3:14 pm
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There is no difference in the mapper itself. In the Nantettatte Baseball cart, the secondary cart, if present, gets mapped into the upper 128K of CHR otherwise is open-bus. It also has WRAM, but otherwise functions the same as Afterburner, which actually uses 2 x 128KB CHR ROMs as well.

At least it appears it works this way, unfortunately I haven't found a mini-cart to try out. Quite sure it would dump as 256K CHR (lower being normal game CHR, upper being on mini-cart).


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PostPosted: Thu Jun 17, 2010 9:26 am 
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Location: Trieste, Italy
thanks a lot for the answer, bootgod... however, I'm now a bit more confused than before ;)

given that it seems very hard to find precise info on these dual carts, let me see if I have at least git the basic fact correct:

a. Nantettatte Baseball!! was a Sunsoft cart with a small slot where the user can insert a mini cart (I guess with updated teams, or something similar)
b. at least two mini carts were produced: '91 Kaimaku Hen and OB Allstar Hen

first questions: does the picture at your website represent the base cart? is the "sub-slot" visible in the pictures (I am not sure how it is supposed to look like)?

Concerning emulation, I'm a bit puzzled. I discovered that in GoodNES 3.14, two UNIF dumps of the minicarts were included:

Nantettatte!! Baseball '91 Kaimaku Hen (J) [U][!].unf
Nantettatte!! Baseball OB Allstar Hen (J) [U][!].unf

Analyzing these files, they both consist of the same PRG0 and CHR0 blocks (which are exactly the same as the PRG and CHR of the base cart) and of a unique PRG1 16k block

I guess these PRG1 chunks contain the additional minicart data (which would seem to contain PRG data rather than CHR... weird).

What somehow concerns me is that I'm not sure where this PRG chunk should be mapped exactly...

NEStopia source seems to handle PRG bankswitching in a very strange way for this board and it's not clear to me if it ever accesses banks beyond 0x10 (which would contain the PRG1 data, if it's loaded right after the base cart PRG). Or maybe the PRG1 data has to be loaded elsewhere and/or mirrored somehow.

I will probably spend some time to further debug these games in the weekend, but I hoped it could have been easier because there are several issues with higher priority in MESS... :(


A last question (even if I know that without a minicart to do experiments, it's hard to give answers): if the minicarts turn out to contain only PRG data, would you still expect 256k CHR? would it possibly be VRAM? does the PCB of the base cart offer any hint?


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PostPosted: Thu Jun 17, 2010 5:38 pm 
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You can't really see the slot on the pic on the site, the cart is 2x as thick as a normal cart on the top, and the mini-cart slides into the fat part from below. Looking at the cart from the side, it kinda looks like a 'P'

I wasn't aware the mini-carts had been dumped, perhaps I woulda looked into this more in the past :)

Is it possible that the game is storing code in the CHR data and moving to to RAM for execution? or the the ROM is simply misclassified as PRG1 instead of CHR1? If you have the ROM, it should be easy enough to tell what kind of data it is.

As for the size, it certainly wouldn't need to be 128K, that is just the maximum. I would guesss the 16K would be mirrored throughout that segment.

Since you said it was a UNIF, is the dumper info block filled by chance? Maybe someone we can direct some more questions too? :)


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