Romdisk Swapping

Author: Lerabot

Introduction

When I started adding things to the ROM disk, I didn't realize that my 10MB+ .elf file would be problematic (i.e. not load) on the Dreamcast. Also it's been mentioned in a forum topic that loading a romdisk instead of multiple files would be faster. I also think that it could be a neat way to handle/manage your memory altogether.

Guide

Step 1

Organizing the content or your romdisk in multiple folders:

 /level1
 /level2
 /level3

Step 2

In your Makefile, duplicate the usual romdisk generation command but change the romdisk name and directory. I also added GZip compression, however sometimes GZip-ed files fail to load. If thats the case for you then don't bother with GZip.

 romdisk.img:
       $(KOS_GENROMFS) -f romdisk.img -d path/to/romdisk -v              # <- this is the usual romdisk command, you can still keep this
       $(KOS_GENROMFS) -f romdisk_name.img -d path/to/romdisk_folder -v  # <- this is your new romdisk, replace the romdisk_name and romdisk_folder with what you want.
       $(KOS_GENROMFS) -f level1.img -d path/to/level -v                 # <- if I'm using the exemple from earlier, I could make a "level1" romdisk this way
       gzip -f -9 romdisk_name.img                                       # <-make sure you add all your new romdisk names here

Note: the leading whitespace consists of a tab, not spaces.

Step 3

In your code you'll need a way to load those new romdisks, we'll use this code snippet by BlackAura. For more info, check this topic [1]

 #include <kos.h>
 #include <zlib/zlib.h>
 
 // Thanks BlackAura ;)
 int mount_romdisk(char *filename, char *mountpoint) {
   void *buffer;
   int length = zlib_getlength(filename);
 
   // Check failure
   if(length == 0)
       return 0;
 
   // Open file
   gzFile file = gzopen(filename, "rb");
   if(!file)
       return 0;
 
   // Allocate memory, read file
   buffer = malloc(length);
   gzread(file, buffer, length);
   gzclose(file);
 
   // Mount
   fs_romdisk_mount(mountpoint, buffer, 1);
   return 1;
 }

It is important that your mount point start with a '/' -> "/level1" and not "level1"

You can now unload the romdisk using:

 fs_romdisk_unmount(mountpoint);

Usage with a Broadband adapter or dc-ipload

In order to use these new romdisk, you need to enable /pc redirection in your dc-tool, update your dc-tool command to use -c:

 dc-tool-ip -t dreamcast -c /path/to/project -x program_name.elf

You can now use the function below to access files in the /rom folder:

 mount_romdisk("/pc/romdisk_name.img.gz", "/rom");

Keep in mind that you'll have to switch /pc/ to /cd/ when you burn this to a CD.