Nitrofs

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Nitrofs Filesystem Driver for Nintendo DS

Contents

What is it?

The nitrofs driver allows accessing of files from a read-only nitro-filesystem that is appended to the end of an .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.

Isnt there already a way to do this?

The previous solutions to 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.

Releases

The 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 file. (In this case to play a wuvry song from the Lotus Land Story by Zun.)

Nitrotstprojectv0.1.tar.bz2

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. No need to ask the end user to copy over alot of seperate files and clutter up their flashcard. :D

For some emulators you may need to use a .sc.nds or ds.gba formatted file. This due to the lack of dldi support among the majority of emulators. In such a case nitrofs will automagically switch to gba mode and read the filesystem as if it were a gba card instead. This requires no changes to the code at all, only that ndstool be used to create a sc.nds or ds.gba style file as follows:

ndstool -c myhomebrew.ds.gba -d MyNitroFS

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 this with the name of your .nds file. You could try using argv[0] here (which points to the current file) but as of this writing it is not supported on all cards.

Lastly open a file as you would in any other OS 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.. buy 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, or are not using the correct build for emulators not supporting DLDI (which are most of em'). This can be done somewhat like this:

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("myndsfile.nds")) {
	fd=open("nitro:/myreadonlynitrofsfile.txt",O_RDONLY);
	if(fd) {
		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");
		printf("If using emulators  that do not support fat/dldi (such as no$gba) be sure you are using a nds.gba or .sc.nds build.\n");
	}
}

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