NitroROM File System Specifications

Note that this document has been reworded in an attempt to circumvent possible 
watermarking measures. No pertinent information has been lost. 
Introduction

This document describes a simple file system which can be used to speed up 
development time, and where the program and data files map into ROM. Application 
developers need not concern themselves with the format of the file system; an API is
provided. 

Details within this document may change before final release. 
Data Format

A NitroROM file has the following constituents. 
Header:
16KB of management stuff.
Startup static blocks:
Modules for the Main and Sub systems that are loaded and executed on startup.
File name table:
Array associating file names with numbers.
Overlay header:
Links for main and sub systems between file numbers and overlay IDs.
File allocation table:
Array of file numbers and ROM positions.
File Images:
Take a guess what these do.

For each block in the file, the developer can specify whether and to what granularity 
the block should be aligned. If alignment is required, padding will be added. 

The ROM header is fixed at the top of the NitroROM file; all other blocks are accessed
by direct or indirect pointers relative to the top of the header. Due to this, it is 
possible for the other blocks to lie in any order in the file. 
ROM Header Format

The following table shows the format of the ROM_Header structure. 
Portion	Offset (hex)	Size	Type	Name	Use	
Reserved for system	000	8 bytes	u8[]	corp_id	Should be "NINTENDO"	
008	24 bytes	u8[]	reserved_A	Unused, should be 0	
Static module params	020	4 bytes	void*	main_rom_offset	Offset of ARM9 startup code in ROM	
024	4 bytes	void*	main_entry_address	Entry address [unimplemented]	
028	4 bytes	void*	main_ram_address	ARM9 destination RAM address	
02C	4 bytes	u32	main_size	Size to copy for ARM9 code	
030	4 bytes	void*	sub_rom_offset	Offset of ARM7 startup code in ROM	
034	4 bytes	void*	sub_entry_address	Entry address [unimplemented]	
038	4 bytes	void*	sub_ram_address	ARM7 destination RAM address	
03C	4 bytes	u32	sub_size	Size to copy for ARM7 code	
Nametable params	040	4 bytes	ROM_FNTDir*	fnt_offset	Offset of name table in ROM	
044	4 bytes	u32	fnt_size	Size of table	
FAT params	048	4 bytes	ROM_FAT*	fat_offset	Offset of allocation table	
04C	4 bytes	u32	fat_size	Table size	
Overlay header params	050	4 bytes	ROM_OVT*	main_ovt_offset	ARM9 overlay offset in ROM	
054	4 bytes	u32	main_ovt_size	Size of ARM9 overlay	
058	4 bytes	ROM_OVT*	sub_ovt_offset	ARM7 overlay offset	
05C	4 bytes	u32	sub_ovt_size	Size of ARM7 overlay	
Reserved	060	16 bytes	u8[]	reserved_B	Should be 0	
070	3984 bytes	u8[]	reserved_C	Again with the 0's	
100	12288 bytes	u8[]	reserved_D	And again	
Startup Module

This is a supplied binary, linked in with the application ELF. The binary is placed in 
ROM without modification. The top ROM address for both processors must be aligned 
at a 512 byte boundary. 

File Name Table

This table associates file names with IDs. The table is built up from two sub-tables: a 
table of directories, and a file table. Directories are distinguished from files by their 
ID: a file can only have an ID in the range of 0x0000-0xEFFF, and a directory has an 
ID of 0xF000-0xFFFF. Therefore, there can be a maximum of 61440 files and 4096 
directories. 
Directory sub-table

The size of the directory table implies the number of entries within it; the subscript of 
a given entry corresponds to a directory ID of subscript+0xF000. 

The following table specifies the format of the ROM_FNTDir structure. 
Offset (hex)	Size	Type	Name	Use	
000	4 bytes	u32	entry_start	Offset of the constituent file sub-table	
004	2 bytes	u16	entry_file_id	ID of first file in the file sub-table	
006	2 bytes	u16	parent_id	ID of parent directory	

The directory with ID 0xF000 is the root directory. In this case, the parent_id field 
holds the number of directories contained within the filesystem, since it has no 
parent. 
File sub-table

An entry in a file sub-table can be produced with either of two structures; one 
describes a file entry, and one a directory reference. The developer must choose 
which structure to use dependent on the circumstances. 

The following table describes a ROM_FNTStrFile entry. 
Offset (hex)	Size	Type	Name	Use	
000	Bitfield: 1 bit	u8	entry_type	0 for a file	
000	Bitfield: 7 bits	u8	entry_name_length	Length of entry name	
001	[length] bytes	char[]	entry_name	File name (NOT zero terminated)	

This table describes a ROM_FNTStrDir structure. 
Offset (hex)	Size	Type	Name	Use	
000	Bitfield: 1 bit	u8	entry_type	1 for a dir	
000	Bitfield: 7 bits	u8	entry_name_length	Length of entry name	
001	[length] bytes	char[]	entry_name	Dir name (NOT zero terminated)	
[length]+1	1 byte	u8	dir_id_L	Directory sub-table ID, low byte	
[length]+2	1 byte	u8	dir_id_H	Directory sub-table ID, high byte