Nitrofs

Revision as of 07:18, 20 May 2008

Nitrofs Filesystem Driver for Nintendo DS

What is it?

Nitrofs is a driver that allows accessing of files from a read-only nitro-filesystem appended to the end of a .nds file. This is how commercial carts store additional data and allows the homebrew app to only load into RAM what is currently needed by the game. In this way data such as large audio files, stage/level specific graphics, can be used without running out of memory.

Since all the game data is stored in one file along with the game or application itself there is no need to ask the end user to copy over alot of seperate files and clutter up their flashcard. :D Additionally this makes it slightly more difficult for inexperienced morons to change the graphics or audio of your game and call it their own than if all the data files were exposed as individual files on the flash card.

Releases

Latest release : Nitrofs Driver v0.2.tar.bz2
Previous release: Nitrofs Driver v0.1.tar.bz2

The project archive contains three source files:

nitrofs.c - The nitro filesystem source.

nitrofs.h - The nitro filesystem header. This should only be included into the file where you have your nitroFSInit() call.

main.c - A working example that demonstrates using the filesystem, reading directories, and reading from a embedded audio file. In this case a wuvry song from the game Lotus Land Story by Zun which has the filename Th04_01.raw. Please enjoy.

The archive also contains an entire working example project and can be built by typing 'make' in the nitrotst directory as you would any other project using devkitPro.

Functional executable file of the latest test release in .nds format, as well as copies of the archives and raw source files, can be found here and may be useful for evaluation and testing.

Recent Changes

• Eliminated the need for .gba formated files. Now the .nds file should work with both emulators and flashcards. (thx wintermutes) :DD
• Fixed bug in fseek. SEEK_CUR should now work properly.

More information can be found on the Discussion. Feel free to ask questions, report bugs, or comments here. ^^

Creating the filesystem

You place all the stuff you want to have on the filesystem into a directory. For this example we have a directory named "MyNitroFS". This directory, its subdirectories, and all contents are then converted into nitro filesystem format and appended onto your executable using ndstool's -d option. Like So:

ndstool -c myhomebrew.nds -d MyNitroFS

Thats it, now all the stuffs in MyNitroFS dir is elegantly appended into one nice pretty file. XD

Note: Do not use the -o option with ndstool for embedding wifi logos, this will break emulator support!

Reading from nitrofs

Firstly, you'll need this includes:

#include <nds.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include "nitrofs.h" //only needed in the file where nitroFSInit() function is called.
#include <fat.h>

Then you will need to initialize the FAT driver, and the nitrofs driver:

fatInitDefault();
nitroFSInit("myndsfile.nds"); //See Notes Below

• Replace 'myndsfile.nds' with the name of your .nds file so the driver knows where to find it. There may be problems if the end user places the homebrew file in an odd place like in an /apps/ directory. You could try to avoid this using the argv[0] argument passed to main() here (which points to the current file) however as of this writing it is not supported on all cards or loaders. So for now its prolly safest to just inform the end user that the file must be placed in the root directory of the card. Another option is 'ndsloader', the newest version seems to support argv passing and would make a good intermediate step as card companies update their firmware.

Lastly open a file as you would on any other system specifying nitro: as the drive:

fd=open("nitro:/Th04_01.raw",O_RDONLY);
read(fd, myBuffer, mybufferSize);
close(fd);

(Author's Note: Really dislike that they did not use Unix style nodes for drives and devices such as '/dev/device' or '/media/drive'. Instead opting for DOS 'drive:' style.. but jaja.. it works :D )

You may want to add some error checking and reporting in case the filename or filepath passed to nitroFSInit are incorrect, the card does not support DLDI. This can be done somewhat like this:

//Path to this executable containing nitrofs
#define FILENAME "myndsfile.nds"
 
int fd;
bool imfat;	//indicate fat driver loaded properly
printf("initalizing fat\n");
if(fatInitDefault()) {
	imfat=true;
	printf("Success...\n");
} else {
	imfat=false;
	printf("Failed... (normal for some emulators. Dont worry, yet :p)\n");
}
printf("initalizing nitrofs\n");
if(nitroFSInit(FILENAME)) {
	fd=open("nitro:/myreadonlynitrofsfile.txt", O_RDONLY);
	if(fd>=0) {
		len=read(fd,sample,st.st_size);
		close(fd);
	} else {
		printf("read only file open failed\n");
	}
} else {
	printf("Failed...\n");
	if(imfat) { //error if fat was initialized...
		printf("Cannot open %s please check filename and path are correct.\n",FILENAME);
	} else { //error if fat/dldi failed
		printf("FAT/DLDI error, please to ensure your card supports DLDI.\n\n");
	}
}

FAQ

Isn't there already a way to do this?

The previous solutions for appending filesystems to .nds files were kinda suxy. For one thing they were not always compatible with most emulators and cards, or did not use the stdio subsystem as a proper filesystem driver should, instead requiring nonstandard open/close/read calls.

Before there were pretty much two options, GBFS and EFS. GBFS would work on emulators, but not off slot-1 cards, EFS would work off slot1 using DLDI but was was not compatible with most emulators. If you wanted to run your game on emulators AND off slot-1 flash cards you had to use two seperate libraries and use alot of #ifdef #else #endif type stuff because they used different function names, as well as neither (afaik) used stdio calls.

Since nitrofs v0.1 was released EFS has been updated to use stdio calls and fallback to gba reads.

Why can't you make it read/write instead of read only?

Because if DLDI/FAT is not enabled (as is on emulators), it attempts to read it in slot-2 gba mode which is read only. This project was partly created to help solve compatibility issues between different cards and emulators as well as do things in a way that more closely resembles a factory cart which is read only as well. Some people just want to do things in way that more closely resembles actual Nintendo libraries and possibly have dreams of one day doing a commercial release of their homebrew. [1] <_<