megaduck-info

Mega Duck / Cougar Boy Console Info

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).

Web version

References

Credits / Thanks

Sean Riddle, Ruud van Falier, Nitro2k, Toxa, Youkal3, Zwenergy, Inside Gadgets, Kuddel

Software

Homebrew Games / ROM Hacks/ Programs

Browse releases (and find source code links) on the MegaDuck Homebrew and ROM Hack showcase.
- There’s also a view for showing what’s new

Emulators/FPGA Re-implementations

Super Junior SameDuck: Fork of SameBoy with support for MegaDuck Handheld and Laptop models. Has correct audio emulation. Development oriented.
MAME, Arcade DB Entry, Cart list xml
SameDuck branch of SameBoy (modified version of SameBoy, not pre-built)
MiSTer: Has correct audio emulation
Analogue Pocket OpenFPGA core

Development Tools

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
  Music / SFX
Mega Duck port of the hUGE Driver Game Boy music driver
Mega Duck port of the CBTFX Game Boy Sound FX driver
Peripherals
Mega Duck Laptop GBDK Examples Sample code for interfacing with the MegaDuck Laptop model Keyboard and RTC (Quique and Junior Computer). See related partial docs
Audio recordings of the 6 built-in speech phrases for the German and Spanish MegaDuck Laptop models

Homebrew Music Tools

Droneboy for MegaDuck

ROM Patches

Patches for running Game Boy games on the MegaDuck

See the MegaDuck Homebrew and ROM Hack showcase

Individual Links:

Patch for the Mega Duck Dice Block game to disable the timer
Patch for Game Boy Tetris
Patch for Game Boy Super Mario Land
Patch for Game Boy Fydo’s Magic Tiles

Hardware

Serial Link Port

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

Cartridge Pinout

Mega Duck Cart Dumping
Scans:
- OEM (Pile Wonder) Front / Back
- IG 32K Front / Back

AC Adapters

Handheld

3.5 mm exterior, 1.35mm interior
6 volts, centrer NEGATIVE polarity

Laptop

3.5 mm exterior, 1.35mm interior
9 volts, centrer POSITIVE polarity
Example picture

MBCs / Bank Switching

MBC Controllers

Laptop model System ROM MBC (CEFA Super Quique, Hartung Super Junior Computer):

Register: Bank selected by writing (0 - 15) to 0x1000. * (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
32K switchable banks
- Sometimes with extension: .md1
- Register: Bank selected by writing 0 - 1 to 0xB000
- Bank Size/Region: Switches the full 32K ROM region
- Games: Puppet Knight, Suleiman’s Treasure
Upper switchable 16K banks
- Sometimes with extension: .md2
- Register: Bank selected by writing 1 - 3 or 1-7 to 0x0001 depending on total ROM size (64K or 128K)
- Bank Size/Region: 16K in the Upper ROM region 0x4000 - 0x7FFF (lower 16K at 0x0000 - 0x3FFF is 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

MBC type per game is according to Reddit

Implementation in emulators

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

System ROMs

Handheld Model: No System/Boot ROM
CEFA Toys Super Quique Laptop Model: Partial disassembly of the System ROM
Hartung Super Junior Computer: …

Porting from Game Boy to Mega Duck

Developing for the Mega Duck is mostly identical (cpu & integrated peripherals) to the Original Game Boy though it has a couple changes listed below.

Most of this research was done by others, I’ve added a small amount.

Summary of Hardware changes versus the Game Boy:

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 toward 0xFFFF / 0x0000
- Laptop Model: Based on System ROM design (no stack init before first call/ret) it appears SP is NOT 0x0000 at power-on
  - Possibly it’s something like 0xFFFE or lower which would allow pushing and popping the stack before init without a resulting crash
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)
Different MBC bank switching register addresses than Game Boy MBCs

Laptop:

Built-in System ROM
Additional Cart Slot for add-on Memory Card (access not yet documented)
Peripherals attached via Serial/Link port
- Keyboard + Piano Keys
- RTC
- Cart
- Detached Gamepad
- Mechanism to launch cartridges in the Cart Slot
- External communication port for the printer (type not yet documented)

Sound Register Value/Data Changes

These changes should be kept in mind when porting Sound Effects and Music Drivers written for the Game Boy.

Registers NR12, NR22, NR42, and NR43 have 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))
Register NR32 has 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)

Sound Register Changes Table

Addr Change means 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

Graphics Register Bit Flag Changes

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

Graphics Register Address Changes

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

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