4000000h 2 R/W DISPCNT LCD Control
4000002h 2 R/W - Undocumented - Green Swap
4000004h 2 R/W DISPSTAT General LCD Status (STAT,LYC)
4000006h 2 R VCOUNT Vertical Counter (LY)
4000008h 2 R/W BG0CNT BG0 Control
400000Ah 2 R/W BG1CNT BG1 Control
400000Ch 2 R/W BG2CNT BG2 Control
400000Eh 2 R/W BG3CNT BG3 Control
4000010h 2 W BG0HOFS BG0 X-Offset
4000012h 2 W BG0VOFS BG0 Y-Offset
4000014h 2 W BG1HOFS BG1 X-Offset
4000016h 2 W BG1VOFS BG1 Y-Offset
4000018h 2 W BG2HOFS BG2 X-Offset
400001Ah 2 W BG2VOFS BG2 Y-Offset
400001Ch 2 W BG3HOFS BG3 X-Offset
400001Eh 2 W BG3VOFS BG3 Y-Offset
4000020h 2 W BG2PA BG2 Rotation/Scaling Parameter A (dx)
4000022h 2 W BG2PB BG2 Rotation/Scaling Parameter B (dmx)
4000024h 2 W BG2PC BG2 Rotation/Scaling Parameter C (dy)
4000026h 2 W BG2PD BG2 Rotation/Scaling Parameter D (dmy)
4000028h 4 W BG2X BG2 Reference Point X-Coordinate
400002Ch 4 W BG2Y BG2 Reference Point Y-Coordinate
4000030h 2 W BG3PA BG3 Rotation/Scaling Parameter A (dx)
4000032h 2 W BG3PB BG3 Rotation/Scaling Parameter B (dmx)
4000034h 2 W BG3PC BG3 Rotation/Scaling Parameter C (dy)
4000036h 2 W BG3PD BG3 Rotation/Scaling Parameter D (dmy)
4000038h 4 W BG3X BG3 Reference Point X-Coordinate
400003Ch 4 W BG3Y BG3 Reference Point Y-Coordinate
4000040h 2 W WIN0H Window 0 Horizontal Dimensions
4000042h 2 W WIN1H Window 1 Horizontal Dimensions
4000044h 2 W WIN0V Window 0 Vertical Dimensions
4000046h 2 W WIN1V Window 1 Vertical Dimensions
4000048h 2 R/W WININ Inside of Window 0 and 1
400004Ah 2 R/W WINOUT Inside of OBJ Window & Outside of Windows
400004Ch 2 W MOSAIC Mosaic Size
400004Eh - - Not used
4000050h 2 R/W BLDCNT Color Special Effects Selection
4000052h 2 R/W BLDALPHA Alpha Blending Coefficients
4000054h 2 W BLDY Brightness (Fade-In/Out) Coefficient
4000056h - - Not used
4000060h 2 R/W SOUND1CNT_L Channel 1 Sweep register (NR10)
4000062h 2 R/W SOUND1CNT_H Channel 1 Duty/Length/Envelope (NR11, NR12)
4000064h 2 R/W SOUND1CNT_X Channel 1 Frequency/Control (NR13, NR14)
4000066h - - Not used
4000068h 2 R/W SOUND2CNT_L Channel 2 Duty/Length/Envelope (NR21, NR22)
400006Ah - - Not used
400006Ch 2 R/W SOUND2CNT_H Channel 2 Frequency/Control (NR23, NR24)
400006Eh - - Not used
4000070h 2 R/W SOUND3CNT_L Channel 3 Stop/Wave RAM select (NR30)
4000072h 2 R/W SOUND3CNT_H Channel 3 Length/Volume (NR31, NR32)
4000074h 2 R/W SOUND3CNT_X Channel 3 Frequency/Control (NR33, NR34)
4000076h - - Not used
4000078h 2 R/W SOUND4CNT_L Channel 4 Length/Envelope (NR41, NR42)
400007Ah - - Not used
400007Ch 2 R/W SOUND4CNT_H Channel 4 Frequency/Control (NR43, NR44)
400007Eh - - Not used
4000080h 2 R/W SOUNDCNT_L Control Stereo/Volume/Enable (NR50, NR51)
4000082h 2 R/W SOUNDCNT_H Control Mixing/DMA Control
4000084h 2 R/W SOUNDCNT_X Control Sound on/off (NR52)
4000086h - - Not used
4000088h 2 BIOS SOUNDBIAS Sound PWM Control
400008Ah .. - - Not used
4000090h 2x10h R/W WAVE_RAM Channel 3 Wave Pattern RAM (2 banks!!)
40000A0h 4 W FIFO_A Channel A FIFO, Data 0-3
40000A4h 4 W FIFO_B Channel B FIFO, Data 0-3
40000A8h - - Not used
40000B0h 4 W DMA0SAD DMA 0 Source Address
40000B4h 4 W DMA0DAD DMA 0 Destination Address
40000B8h 2 W DMA0CNT_L DMA 0 Word Count
40000BAh 2 R/W DMA0CNT_H DMA 0 Control
40000BCh 4 W DMA1SAD DMA 1 Source Address
40000C0h 4 W DMA1DAD DMA 1 Destination Address
40000C4h 2 W DMA1CNT_L DMA 1 Word Count
40000C6h 2 R/W DMA1CNT_H DMA 1 Control
40000C8h 4 W DMA2SAD DMA 2 Source Address
40000CCh 4 W DMA2DAD DMA 2 Destination Address
40000D0h 2 W DMA2CNT_L DMA 2 Word Count
40000D2h 2 R/W DMA2CNT_H DMA 2 Control
40000D4h 4 W DMA3SAD DMA 3 Source Address
40000D8h 4 W DMA3DAD DMA 3 Destination Address
40000DCh 2 W DMA3CNT_L DMA 3 Word Count
40000DEh 2 R/W DMA3CNT_H DMA 3 Control
40000E0h - - Not used
4000100h 2 R/W TM0CNT_L Timer 0 Counter/Reload
4000102h 2 R/W TM0CNT_H Timer 0 Control
4000104h 2 R/W TM1CNT_L Timer 1 Counter/Reload
4000106h 2 R/W TM1CNT_H Timer 1 Control
4000108h 2 R/W TM2CNT_L Timer 2 Counter/Reload
400010Ah 2 R/W TM2CNT_H Timer 2 Control
400010Ch 2 R/W TM3CNT_L Timer 3 Counter/Reload
400010Eh 2 R/W TM3CNT_H Timer 3 Control
4000110h - - Not used
4000120h 4 R/W SIODATA32 SIO Data (Normal-32bit Mode; shared with below)
4000120h 2 R/W SIOMULTI0 SIO Data 0 (Parent) (Multi-Player Mode)
4000122h 2 R/W SIOMULTI1 SIO Data 1 (1st Child) (Multi-Player Mode)
4000124h 2 R/W SIOMULTI2 SIO Data 2 (2nd Child) (Multi-Player Mode)
4000126h 2 R/W SIOMULTI3 SIO Data 3 (3rd Child) (Multi-Player Mode)
4000128h 2 R/W SIOCNT SIO Control Register
400012Ah 2 R/W SIOMLT_SEND SIO Data (Local of MultiPlayer; shared below)
400012Ah 2 R/W SIODATA8 SIO Data (Normal-8bit and UART Mode)
400012Ch - - Not used
4000130h 2 R KEYINPUT Key Status
4000132h 2 R/W KEYCNT Key Interrupt Control
4000134h 2 R/W RCNT SIO Mode Select/General Purpose Data
4000136h - - IR Ancient - Infrared Register (Prototypes only)
4000138h - - Not used
4000140h 2 R/W JOYCNT SIO JOY Bus Control
4000142h - - Not used
4000150h 4 R/W JOY_RECV SIO JOY Bus Receive Data
4000154h 4 R/W JOY_TRANS SIO JOY Bus Transmit Data
4000158h 2 R/? JOYSTAT SIO JOY Bus Receive Status
400015Ah - - Not used
4000200h 2 R/W IE Interrupt Enable Register
4000202h 2 R/W IF Interrupt Request Flags / IRQ Acknowledge
4000204h 2 R/W WAITCNT Game Pak Waitstate Control
4000206h - - Not used
4000208h 2 R/W IME Interrupt Master Enable Register
400020Ah - - Not used
4000300h 1 R/W POSTFLG Undocumented - Post Boot Flag
4000301h 1 W HALTCNT Undocumented - Power Down Control
4000302h - - Not used
4000410h ? ? ? Undocumented - Purpose Unknown / Bug ??? 0FFh
4000411h - - Not used
4000800h 4 R/W ? Undocumented - Internal Memory Control (R/W)
4000804h - - Not used
4xx0800h 4 R/W ? Mirrors of 4000800h (repeated each 64K)
4700000h 4 W (3DS) Disable ARM7 bootrom overlay (3DS only)
All further addresses at 4XXXXXXh are unused and do not contain mirrors of the I/O area, with the only exception that 4000800h is repeated each 64K (ie. mirrored at 4010800h, 4020800h, etc.)