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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

Homebrew Games

Emulators/FPGA Re-implementations

Development Tools

SDKs / Build related

Music / SFX

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 Music Tools

ROM Patches

Hardware

Flash Cartridges

Display mod / LCD Header info

Laptop model Gamepad

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

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

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