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[ImmortalNinja]

Seeing as this question seems to come up a lot I've decided to write a short FAQ guide thingy all about Single Cart MultiPlayer.

I'm not too sure on the technical details and most of this information has been gathered from this board and experimental observation.

Quick Simple version:

Rom games sent from a flashCart will have an invalid RSA signature.
An un-flashed DS receiving such a download game will fail the RSA check and in most cases hang.
There are some games that don’t do this: eg meteos. (Check the as of yet incomplete compatibility list a couple of post down)
So in general only download on flashed DS’ unless that game is one of the few where it doesn’t matter. (Meteos, StarFox)
It is possible to host a game from a Un-flashed DS, however it will still fail when sending to another un-flashed DS.

[ImmortalNinja]

Long verbal diarrhea version:

Introduction
The Nintendo DS is a great handheld gaming device that comes with built in Wi-Fi to allow several players to participate in MulitPlayer games.
In general there are two multiplayer modes:

Multi-Cart:
This is where every player has a copy of the game. Because everyone has a copy of the game this mode generally works with no problems using any combinations of orginal carts and superCards, flashed and non-flashed DS'  

Single-Cart Download Play:
This is where only one player (the host) needs to have a copy of the game. All other players then download the multiplayer game from the host.
[/list]

Single-Cart Download Play
This is a great mode as it means not everyone has to have a copy of the game to participate in a fun multiplayer session. However because each DS has to download the game engine and resources from a single DS it does take a bit of time and the game is usually cut down.
Mario Kart for instance only has a limited number of tracks.

Problems and Why
Alas due to the nature of download play, using a flashCart to do this can lead to problems. Well, one problem really, it just doesn’t work. This is usually manifested by the DS' connecting and then shortly after downloading hanging on a particular screen.
This is because when using download play the DS will do some security checks to make sure arbitrary code is not being run.
For a Rom to work from a flashcart it is patched/decrypted/dumped whatever and this process messes up the RSA code.
When this game is sent to other DS’ for Download play the receiving DS does a quick check on the RSA, doesn’t like it and hangs.
This is proably the result of Nintendo blocking the Wi-Fi me exploit:

“Flashme allows to transmit and receive unencrypted data, when nintendo blocked Wifime with it's last update, the unencrypted data will make a New firm NDS crash.”

http://scdev.org/forum/viewtopic.php?t=2387&start=0&postdays=0&postorder=asc&highlight=%5B%2Fquote%5D

Getting it to Work

1- Use an Orginal Cart:
The easiest way to ensure it works is to buy an orginal Cart. The RSA code remains intact and everyone can happily download. If a game is good and you and you’re friends are going to play it a lot this is by far the best option.

2-Stick to Certain games:
Some games still work even though the RSA check fails.
Such as Polarium, Meteos, Bomberman and StarFox.
I’m not sure why this is, maybe the game is coded such that failed RSA’s are ignored or when the game got dumped the RSA signature was fine. Don’t know, but suffice to say these games appear to work with not problems. At the moment I’m compliling a very long list of games with multiplayer options and whether they work or not.

Use the FlashMe bios:
The flashMe bios bypasses the RSA check. Again I’m not entirely sure how it does this but the important thing is it can download and run unverified/unencrypted data. That is to say if your DS is flashed is can download a download game from any host.
This leads to a nice workaround if you have just one DS which isn’t flashed. By using a superKey you can host the game from a superCard on the Non-flashed DS. Provided that all the other DS’ that are downloading are flashed this should work no problem.
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It might be possible, in theory, to patch the ROM, edit FlashMe, edit SuperCard so that when a game is sent the RSA code is intact but that sounds far to techinical for me to delve into.

I hope this guide helps people and stops the same questions being asked over and over.

If there are any glaring errors please let me know (PM best) and I'll be happy to sort it out.

As I said I'm currently working on a very large compatablity list of games that support multi/single cart multiplayer and whether it works sending to a non-flashed DS. Only on 100 of 500 and its going to take a bit of time so please be patient.

[ImmortalNinja]

Actually, it might be possible to write a homeBrew app that acts as a reciver and then runs the code. This will allow users with a Non-Flashed DS, superKey and SuperCard to play Single Cart games. Of course if you have that you may as well play the multiCart games......
but games like Point Blank only have single Cart multiplayer.

[Pari]

Hi,

I hope one day, a homebrew app will be able to act as receiver as you said. The game brain training also only has single Cart multiplayer. I'm addicted to this game and i'd like to play with non-flashed DS  

[ImmortalNinja]

Well,
for my (rather unpretty) work in progress list:
http://www.immortalninja.com/NDS_DownLoad_Play.htm
These are all the games that are listed on Dual Screen Radio as having single cart support, and were all tested sending from a flashed Lite to a non-flashed Lite.
Some interesting odditites.
My copy of Ridge Racer does download but crashes when the race starts, it does this even when sending to a flashed device.
My (e) version of BrainAge doesnt work by the U version does.

Have no idea what this means but I've got to dash off to work now so I'll investigate further later.
FYI:
Heres the full list of games, so as you can I see I have a ways to go yet.....
http://www.immortalninja.com/NDS_Full.htm

KK

[mgarrine]

very nice work, my compliments :roll: