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.

References

…

Web version

Software

Emulators/FPGA Re-implementations

• 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

Development Tools

SDKs / Build related

• 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 hardware (Quique and Junior Computer), such as the keyboard.

Homebrew Games

• 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

Homebrew Music Tools

• Droneboy for MegaDuck

ROM Patches

• 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

Hardware

Flash Cartridges

• A2 Heaven multi-flash cart
• Inside Gadgets 32K flash cart - Compatible with GBXCart flasher
• 3D Printable cartridge shell

Display mod / LCD Header info

• Ruud van Falier’s DMG IPS adapter mod
• Game Boy Pocket (MGB) to Mega Duck display adapter

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

MBC Controllers

• TODO: mbc types, their common extensions (.md1, .md2, .bin), notes on how different emulators select mbcs

Cartridge Pinout

• Mega Duck Cart Dumping

AC Adapter for Super QuiQue Laptop

• An AC Adapter that worked is: ~3.45mm exterior, ~1.15mm interior, 9 volts central positive polarity. Picture.

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.

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.

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 )
• 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 use 0x2000 - 0x3FFF)
  • TODO: Laptop model system ROM

Sound Register Value/Data Changes

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

1. 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))
2. 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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