GUIDE : romdisk swapping

[lerabot]

I've been messing with this today and figured that it might be interesting for others

WHY DO ROMDISK SWAP?
when I started adding things to the rom disk, I didn't realize that my 10mb+ .elf file would be problematic (ie : not load) on the dreamcast. also,
it's been mentionned in other topic that loading the romdisk and not multiple files would be faster. I also think that it could be a neat way to handle/manage your memory altogether.

HOW-TO

1 - organize the content or your romdisk in folders

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/level1
/level2
/level3

2 - in your makefile, duplicate the usual romdisk command but change the romdisk name and directory. i also added gzip compression.

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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

3 - in your code you'll need a way to load those new romdisks, we'll use this good code snippet BlackAura gave us a while ago. for more info, check this topic : viewtopic.php?f=29&t=68795&hilit=romdisk+feet+of+fury

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#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 :

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fs_romdisk_unmount(mountpoint);

HOW-TO USE WITH BBA / 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

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

you can now use the function below to acces files in the /rom folder

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

keep in mind that you'll have to switch /pc/ to /cd/ when you'll end up burning this to a CD.

PLEASE LET ME KNOW IF SOMETHING IS WRONG/ NOT OPTIMIZED! (also, thanks Quzar for the help on IRC)

[bogglez]

Added to the wiki: http://dcemulation.org/?title=Romdisk_Swapping
Is your other guide ready btw or are you still making modifications?

[lerabot]

Thanks man! I'll look at the other tutorial this weekend.