GCDTool

Tool to create a GCD rom for DSi ntrboot.

Usage

GCDTool --arm9 arm9.elf --arm7 arm7.elf --wram wramConfig.json --rsakey gcdKey.der output.gcd

Arguments

Mandatory

• --arm9 specifies the arm9 elf file;
• --arm7 specifies the arm7 elf file;
• --wram specifies the wram configuration json file (see below);
• --rsakey specifies the der file with the RSA private key to use.

The arm7 and arm9 binaries should have a load address in internal ram (for example TWL wram), as main memory is not yet enabled when the GCD rom is booted.

Optional

• --gamecode specifies the 4 character game code to use (default: ####);
• --arm9-67-mhz runs the arm9 at 67 MHz instead of 134 MHz.

Wram configuration JSON file

Specifies the initial wram configuration to use.

Example

{
    "wramA": {
        "arm7": { "start": "0x03800000", "length": "0x40000", "slots": "all" },
        "blocks": [
            { "master": "arm7", "slot": 0 },
            { "master": "arm7", "slot": 1 },
            { "master": "arm7", "slot": 2 },
            { "master": "arm7", "slot": 3 }
        ]
    },
    "wramB": {
        "arm9": { "start": "0x03800000", "length": "0x40000", "slots": "all" },
        "blocks": [
            { "master": "arm9", "slot": 0 },
            { "master": "arm9", "slot": 1 },
            { "master": "arm9", "slot": 2 },
            { "master": "arm9", "slot": 3 },
            { "master": "arm9", "slot": 4 },
            { "master": "arm9", "slot": 5 },
            { "master": "arm9", "slot": 6 },
            { "master": "arm9", "slot": 7 }
        ]
    },
    "wramC": {
        "arm9": { "start": "0x03840000", "length": "0x40000", "slots": "all" },
        "blocks": [
            { "master": "arm9", "slot": 0 },
            { "master": "arm9", "slot": 1 },
            { "master": "arm9", "slot": 2 },
            { "master": "arm9", "slot": 3 },
            { "master": "arm9", "slot": 4 },
            { "master": "arm9", "slot": 5 },
            { "master": "arm9", "slot": 6 },
            { "master": "arm9", "slot": 7 }
        ]
    },
    "ntrWram" : [ "arm7", "arm7" ],
    "vramC": 7,
    "vramD": 7
}

TWL wram mapping

For TWL wram A, B and C the mapping in memory can be specified for both the arm9 and arm7 side with the "arm9" and "arm7" properties (can be omitted to not map the ram at all). Start and length must be 64 kB aligned for wram A, and 32 kB aligned for wram B and C. "slots" specifies which slots are actually mapped in memory, and as such also the size of the mirroring. For wram A the options are "0" (64 kB), "01" (128 kB) and "all" or "0123" (256 kB). For wram B and C the options are "0" (32 kB), "01" (64 kB), "0123" (128 kB) and "all" or "01234567" (256 kB).

TWL wram block mapping

For each block of TWL wram the following properties are available:

• "master" specifies what the block is mapped to. All wrams support "arm9" and "arm7", and wram B and C additionally support "dsp" for dsp code and data respectively;
• "slot" specifies the slot the block is mapped to;
• "enabled" specifies whether the block is enabled. This defaults to true and can be omitted;
• "locked" specifies whether the mapping of the block should be locked, such that the arm9 cannot change it. This defaults to false and can be omitted.

When "enabled" is set to false, "master" and "slot" can be omitted.

NTR wram mapping

Specifies for the two NTR wram blocks whether they are mapped to "arm9" or "arm7".

Vram mapping

Not sure how this works. There are only 3 bits available, but the vram C and D mapping registers need more bits properly specify the mapping and enable it. Default value is 7 for both.

Booting the GCD rom

The GCD rom needs to be flashed to a (dev) flashcard or other means of emulating a DS cartridge. Make sure the blowfish table is used that is included in the generated .gcd file (p table at 0x1600 and s boxes at 0x1C00).

With the cartridge inserted, the GCD rom is booted by putting a small magnet between the ABXY buttons (to trigger the lid close detection), holding START, SELECT and X and pressing the power button.