Dual Mask Rom cart to Single Mask Rom donor

DNSDies · Post by **DNSDies** » Tue Jul 10, 2012 11:36 pm

Is this possible?

I'd like to put Clock Tower in a spare Japanese copy of Donkey Kong Country 2.

The rom file has an odd size, can I just repeat the rom to fill a 32mbit TSOP package?

Post by **lidnariq** » Wed Jul 11, 2012 1:23 am

Caveat: I have never made a SNES repro.

My understanding is that odd-sized SNES games need to be padded as follows:
* take the first 2ⁿ bytes, where n is as large as possible (in this case, 2ⁿ=2MiB)
* take the remainder (which AFAIK is always 2ⁱ, i<n), repeat that part 2⁽ⁿ¯ⁱ⁾ times
* result is an image 2ⁿ⁺¹ bytes in size.

qwertymodo · Post by **qwertymodo** » Wed Jul 11, 2012 7:51 am

lidnariq wrote:Caveat: I have never made a SNES repro.

My understanding is that odd-sized SNES games need to be padded as follows:
* take the first 2ⁿ bytes, where n is as large as possible (in this case, 2ⁿ=2MiB)
* take the remainder (which AFAIK is always 2ⁱ, i<n), repeat that part 2⁽ⁿ¯ⁱ⁾ times
* result is an image 2ⁿ⁺¹ bytes in size.

Basically this, but then repeat the entire resulting file as necessary to fill the ROM.

DNSDies · Post by **DNSDies** » Wed Jul 11, 2012 8:18 am

so, basically, take the rom file, copy it, then remove the first 2,097,125 bytes, use the resulting file to pad the original rom to 4,194,304 bytes, repeating as necessary?

Actually, looking at another thread, it seems like how one does it is to cut the rom to the nearest multiple 2 Megabits (24 Megabits in this case) and repeat the remainder to fill the EEPROM.

So, Clock Tower seems to be 24Mbit mask rom with an additional 1 Megabit mask rom on the original cart, so I could just repeat that last 1 Megabit to fill from 25Mbit to 32Mbit.

so mirror the last megabit 8 times and append to the 24 Mbit rom?

Post by **lidnariq** » Wed Jul 11, 2012 11:06 am

The translated version seems to be 25Mbit, the original is 24Mbit. While the instructions you gave there are probably correct, I have no idea and I don't know how to verify the padded image will work correctly.

The game probably doesn't rely on the mirrored bits at the end and you might be even just able to pad it with FFs, but unless e.g. bsnes will let you feed it either padded image and you play through the entire game first to find out, I'd be worried about something going wrong.

DNSDies · Post by **DNSDies** » Wed Jul 11, 2012 1:50 pm

that's a shame.

I guess I can test it out on BSNES for a while.

I'm not sure a tsop package can be reprogrammed once assembled on my willem programmer, so I'll have to test it before soldering it.

qwertymodo · Post by **qwertymodo** » Wed Jul 11, 2012 1:51 pm

The game's coding doesn't care what the padding is. Mirroring the ROM rather than padding simply ensures that the ROM operates properly if the upper address lines are left floating. However, for a 24 Mbit ROM on a 32Mbit chip, this won't be an issue. In that case, you don't even have to pad the ROM at all. For a ROM less than half the size of the chip you're using, however, mirroring is typically a good idea.

MottZilla · Post by **MottZilla** » Wed Jul 11, 2012 4:50 pm

Why destroy a good game like DKC2? Take the time to find shitty sports games no one likes or wants. At the very least save the maskrom.

DNSDies · Post by **DNSDies** » Thu Jul 12, 2012 8:33 am

It's a Japanese copy, and the mask rom is damaged due to some corrosion on some of the address pins.

It was part of an as-is bundle of Japanese games I got for $25 that included:

Seiken Densetsu 2 (which needs serious cleaning and the contacts tinned with solder to prevent further corrosion, I'm thinking of converting it to Seiken Densetsu 3)

Kirby Super Star (which needed a little cleaning, but works fine)

DKC2 (had some serious water damage, label is ruined, mask rom is rusted on the legs, boots after cleaning but crashes during gameplay)

Star Fox (ruined label, but board is an epoxy blob and virtually indestructible)

Mario Cart, which was in pretty much pristine condition

MottZilla · Post by **MottZilla** » Thu Jul 12, 2012 9:22 am

I'm glad you have a good reason. Are you sure the corrosion cannot be dealt with? So you bought a lot of games someone took a bath with?

qwertymodo · Post by **qwertymodo** » Fri Jul 13, 2012 8:57 am

If the corrosion is unfixable, the board may be unusable as a donor as well. Try desoldering the mask ROM and cleaning up the pins with steel wool or something as best you can, then flux the crap out of them and resolder them back in. It's at least worth a shot. And if you still plan to use it as a donor anyway, at least it'd be good to check.

DNSDies · Post by **DNSDies** » Fri Jul 13, 2012 9:06 am

The corrosion is pretty bad.
I can't even get to the solder on a few of the pins due to it.

My desoldering pump can't liquify it enough, so I've had to use a dremel to cut, drill, and clean the contacts.

The guy I bought these from found them after the flooding and earthquake/tsunami in Japan.
Some are in bad shape, others just need some love.

The board itself is pretty usable, continuity testing with a multimeter shows the board is pretty sound, just that some of the exposed metal parts are corroded to the point where no repair can save them for less than the cost of a new cart.