A collection of technical information and resources for the Mega Duck console brought together in one place. Much of it researched by others, some by me (minor sound reg fixes, laptop model docs, some ports and patches, etc).
- Sean Riddle
- MAME: 1 2 3
- MiSTer
- Toxa's Port of 0x7f's Black Castle to the Mega Duck
- 32K version that fits on Inside Gadgets 32K cart
- Mega Duck games collection on itch.io
- SystemofLever's GB Fireplace ported for the MegaDuck
- MWehrstedt's Max Pirate ported for the MegaDuck
- Nitro2k's whichboot.gb ported for the MegaDuck
- MAME, Arcade DB Entry, Cart list xml
- SameDuck branch of SameBoy (modified version of SameBoy, not pre-built)
- MiSTer at present the only one with all known audio register changes integrated, so that music and sfx play correctly
- Analogue Pocket OpenFPGA core
- GBDK-2020: C dev kit, supports Mega Duck as a build target
- hardware.inc for MegaDuck: Hardware constants and addresses for use with asm/RGBDS
- Newer hardware.inc base version
- Mega Duck port of the hUGE Driver Game Boy music driver
- Mega Duck port of the CBTFX Game Boy Sound FX driver
- Mega Duck Laptop GBDK Examples Sample code for interfacing with the MegaDuck Laptop model hardware (Quique and Junior Computer), such as the keyboard. See related partial docs.
- Patch for the Mega Duck Dice Block game to disable the timer
- Patch for Game Boy Tetris so it runs on the Mega Duck
- Patch for Game Boy Fydo's Magic Tiles
- Open-source RP2040-based flash cart
- A2 Heaven multi-flash cart
- Inside Gadgets 32K flash cart - Compatible with GBXCart flasher
- 3D Printable cartridge shell
Laptop model System ROM MBC (CEFA Super Quique, Hartung Super Junior Computer):
- Register: Bank selected by writing (
0 - 15) to0x1000. * (Bank num starting with 0 needs to be re-checked) - Bank Size/Region: Switches the full 32K ROM region
- Note: Uses a delay of ~41 M-Cycles (executed from WRAM) after writing the bank switch before resuming execution from ROM. Unclear if required.
OEM Games:
- 32K with NO switchable banks
- Sometimes with extension:
.bin, but that may also be used for banked ROMs with some emulators - Games: Arctic Zone, Bomb Disposer, Magic Maze, Pile Wonder, Street Rider, The Brick Wall, Trap and Turn, Vex
- Sometimes with extension:
- 32K switchable banks
- Sometimes with extension:
.md1 - Register: Bank selected by writing
0 - 1to0xB000 - Bank Size/Region: Switches the full 32K ROM region
- Games: Puppet Knight, Suleiman’s Treasure
- Sometimes with extension:
- Upper switchable 16K banks
- Sometimes with extension:
.md2 - Register: Bank selected by writing
1 - 3or1-7to0x0001depending on total ROM size (64K or 128K) - Bank Size/Region: 16K in the Upper ROM region
0x4000 - 0x7FFF(lower 16K at0x0000 - 0x3FFFis fixed bank 0) - Games: 2nd Space, Ant Soldiers, Armour Force, Beast Fighter, Black Forest Tale, Captain Knick Knack, Commin Five in One, Duck Adventures, Four in One, Magic Tower, Railway, Snake Roy, Worm Visitor, Zipball
- Sometimes with extension:
MBC type per game is according to Reddit
Game Boy ROMs contain an embedded meta-data header which (usually) indicates the type of MBC (Memory Bank Controller) used. This allows emulators to automatically emulate the correct cart hardware (the Game Boy hardware itself ignores this and doesn't need it since the cart hardware is present).
OEM Mega Duck ROMs lack this header which means that emulators have to use other methods to infer what type of cart MBC is required by a given ROM.
The main methods for selecting the right MegaDuck cart MBC:
- By File Extension (
.md1= 32K banks,.md2= Upper 16K Banks,.bin= 32k no mbc)- Analogue Pocket OpenFPGA MegaDuck Core
- By hashes of the ROMs
- MAME (partially)
- By emulating both MBC styles at the same time in case a game uses either. This works since the two MBCs use a different register address.
- MAME (partially), MiSTer
- Info for building a replacement Gamepad / "Mouse" for the MegaDuck Laptop model
- The link port has a different conenctor style (bare header) than the Game Boy, but the pin order and signals appear to be the same. With the use of a connector style adapter a Mega Duck and a Game Boy can exchange data over their link ports. Catskull has Game Boy link port parts that can be used to build an adapter.
- The serial link registers appear to have the same address, control flags and behavior as a classic Game Boy
- Mega Duck Cart Dumping
- Scans:
- An AC Adapter that worked is: ~3.45mm exterior, ~1.15mm interior, 9 volts central positive polarity. Picture.
- Handheld Model: No System/Boot ROM
- CEFA Toys Super Quique Laptop Model: Partial disassembly of the System ROM
- Hartung Super Junior Computer: ...
Developing for the Mega Duck is mostly identical (cpu & integrated peripherals) to the Original Game Boy though it has a couple changes listed below.
Register and flag names will mostly follow those in the Game Boy dev hardware.inc, but may have some GBDK-isms.
Most of this research was done by others, I've added a small amount.
Physical / Hardware:
- Different cartridge pinout / connector
- Different serial link port connector shape
Programming:
- No Boot ROM
- Cartridge Boot Logo: not present on Mega Duck
- Cartridge Header data: not present on Mega Duck
- Checksum header: not present on Mega Duck. Do not apply checksum to ROM after building as on the Game Boy
- Program Entry Point:
0x0000(on Game Boy:0x0100) - Initial registers
- Handheld Models: (
AF, BC, DE, HL, SP) are random at startup (due to lack of boot rom) with some affinity toward0xFFFF/0x0000 - Laptop Model: Based on System ROM design (no stack init before first call/ret) it appears SP is NOT
0x0000at power-on- Possibly it's something like 0xFFFE or lower which would allow pushing and popping the stack before init without a resulting crash
- Handheld Models: (
- Serial control
- Laptop Mode: Based on System ROM design and behavior it seems possible to use SC and SB reg outside normal GB guidelines (Sending still works when triggering SC to send before loading the send value into SB).
- Display registers address and flag definitions: Some changed (details below)
- VRAM data:
- The user program should clear it before use.
- For Handhelds: since a boot ROM does not run on startup it means Tile Map and Pattern data are not cleared and will have (consistent) random data.
- For Laptop models: The System ROM will not clear VRAM before launching a user program from the system menu. The font patterns left in VRAM on program startup can be used to tell the difference between the Super Quique (Spanish) and Super Junior (German) laptop models. See example code.
- Audio registers address and flag definitions: Some changed (details below)
- MBC ROM bank switching register address:
0x0001(many Game Boy MBCs use0x2000 - 0x3FFF)- TODO: Laptop model system ROM
These changes should be kept in mind when porting Sound Effects and Music Drivers written for the Game Boy.
- Registers
NR12, NR22, NR42, and NR43have their contents nybble swapped.- To maintain compatibility with the Game Boy the value to write (or the value read) can be converted this way:
((uint8_t)(value << 4) | (uint8_t)(value >> 4))
- To maintain compatibility with the Game Boy the value to write (or the value read) can be converted this way:
- Register
NR32has the volume bit values changed.Game Boy: Bits:6..5 : 00 = mute, 01 = 100%, 10 = 50%, 11 = 25%Mega Duck: Bits:6..5 : 00 = mute, 01 = 25%, 10 = 50%, 11 = 100%- To maintain compatibility witht he Game Boy the value to write (or the value read) can be converted this way:
(((~(uint8_t)value) + (uint8_t)0x20u) & (uint8_t)0x60u)
Addr Changemeans deviation from the expected linear incrementing register address order per sound channel that the Game Boy registers follow. The shuffled order on the Mega Duck can break assumptions in Game Boy sound drivers which attempt to write each channel as a sequential block using an incrementing register pointer.
| Reg | Alt Name | Game Boy | Mega Duck | Data Change | Addr Change |
|---|---|---|---|---|---|
| NR10 | rAUD1SWEEP | 0xFF10 | 0xFF20 | ||
| NR11 | rAUD1LEN | 0xFF11 | 0xFF22 | Addr +1 | |
| NR12 | rAUD1ENV | 0xFF12 | 0xFF21 | nybble swap | Addr -1 |
| NR13 | rAUD1LOW | 0xFF13 | 0xFF23 | ||
| NR14 | rAUD1HIGH | 0xFF14 | 0xFF24 | ||
| NR21 | rAUD2LEN | 0xFF16 | 0xFF25 | Addr -1 | |
| NR22 | rAUD2ENV | 0xFF17 | 0xFF27 | nybble swap | |
| NR23 | rAUD2LOW | 0xFF18 | 0xFF28 | ||
| NR24 | rAUD2HIGH | 0xFF19 | 0xFF29 | ||
| NR30 | rAUD3ENA | 0xFF1A | 0xFF2A | ||
| NR31 | rAUD3LEN | 0xFF1B | 0xFF2B | ||
| NR32 | rAUD3LEVEL | 0xFF1C | 0xFF2C | volume bit swizzle | |
| NR33 | rAUD3LOW | 0xFF1D | 0xFF2E | Addr +1 | |
| NR34 | rAUD3HIGH | 0xFF1E | 0xFF2D | Addr -1 | |
| NR41 | rAUD4LEN | 0xFF20 | 0xFF40 | ||
| NR42 | rAUD4ENV | 0xFF21 | 0xFF42 | nybble swap | Addr +1 |
| NR43 | rAUD4POLY | 0xFF22 | 0xFF41 | nybble swap | Addr -1 |
| NR44 | rAUD4GO | 0xFF23 | 0xFF43 | ||
| NR50 | rAUDVOL | 0xFF24 | 0xFF44 | ||
| NR51 | rAUDTERM | 0xFF25 | 0xFF46 | Addr +1 | |
| NR52 | rAUDENA | 0xFF26 | 0xFF45 | Addr +1 |
| LCDC Flag | Game Boy | Mega Duck | Purpose | |
|---|---|---|---|---|
| LCDCF_B_ON | .7 | .7 | (same) | Bit for LCD On/Off Select |
| LCDCF_B_WIN9C00 | .6 | .3 | Bit for Window Tile Map Region Select | |
| LCDCF_B_WINON | .5 | .5 | (same) | Bit for Window Display On/Off Control |
| LCDCF_B_BG8000 | .4 | .4 | (same) | Bit for BG & Window Tile Data Region Select |
| LCDCF_B_BG9C00 | .3 | .2 | Bit for BG Tile Map Region Select | |
| LCDCF_B_OBJ16 | .2 | .1 | Bit for Sprites Size Select | |
| LCDCF_B_OBJON | .1 | .0 | Bit for Sprites Display Visible/Hidden Select | |
| LCDCF_B_BGON | .0 | .6 | Bit for Background Display Visible Hidden Select |
| Register | Game Boy | Mega Duck |
|---|---|---|
| LCDC | 0xFF40 | 0xFF10 |
| STAT | 0xFF41 | 0xFF11 |
| SCY | 0xFF42 | 0xFF12 |
| SCX | 0xFF43 | 0xFF13 |
| LY | 0xFF44 | 0xFF18 |
| LYC | 0xFF45 | 0xFF19 |
| DMA | 0xFF46 | 0xFF1A |
| BGP | 0xFF47 | 0xFF1B |
| OBP0 | 0xFF48 | 0xFF14 |
| OBP1 | 0xFF49 | 0xFF15 |
| WY | 0xFF4A | 0xFF16 |
| WX | 0xFF4B | 0xFF17 |