Romdisk Swapping

Author: Lerabot/Magnes

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. **Need source** I also think that it could be a neat way to handle/manage your memory altogether.

• 2020 edit : Removed the GZ compression as it seemed to cause problem with filename longer than a certain length (16 IIRC?) *

Guide

Organize your assets

Organize the content or your romdisk in multiple folders:

``` /level1 /level2 /level3 ```

Convert to romdisk

In your Makefile, duplicate the usual romdisk generation command but change the romdisk name and directory.

This is the usual romdisk command, you can still keep this

 $(KOS_GENROMFS) -f romdisk.img -d path/to/romdisk -v              

This is your new romdisk, replace the romdisk_name and romdisk_folder with what you want.

 $(KOS_GENROMFS) -f romdisk_name.img -d path/to/romdisk_folder -v  

If I'm using the example from earlier, I could make a "level1" romdisk this way

 $(KOS_GENROMFS) -f level1.img -d path/to/level -v                 

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;
 
   // 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.