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GBAはメモリを読み書きする感覚でハードウェアを操作することが可能です。アドレスは0x4000000から順次並んでいて、機能の順番としては「液晶ディスプレイ、サウンド、DMA(データ転送)、タイマー、SIO1(外部入出力)、キー入力、SIO2、その他」となっています。I/Oの意味を知ってしまえばGBAに何ができて、何が出来ないのかを理解したも当然です。1つ1つのビットの意味はGBATEKを参照してみることが大事になります。ただGBATEKは日本語の広辞苑というのか、辞書みたいなものなので頭から読むものではありません。必要になったら部分的に参照します。もしGBATEKが難しいと感じるようならば、このWikiのチュートリアルを一通りやれば自然と読み解く方法が身につくと思います。
エミュレータは「Tools -> IO Viewer」で参照可能です。リアルタイムで変更できたりします。
I/O Map Forward The base address for GBA I/O ports is 04000000h - all address below are actually meant to be locat ed at 04000NNNh in memory rather than at NNNh.
LCD I/O Registers 000h R/W DISPCNT LCD Control 002h R/W - Undocumented - Green Swap 004h R/W DISPSTAT General LCD Status (STAT,LYC) 006h R VCOUNT Vertical Counter (LY) 008h R/W BG0CNT BG0 Control 00Ah R/W BG1CNT BG1 Control 00Ch R/W BG2CNT BG2 Control 00Eh R/W BG3CNT BG3 Control 010h W BG0HOFS BG0 X-Offset 012h W BG0VOFS BG0 Y-Offset 014h W BG1HOFS BG1 X-Offset 016h W BG1VOFS BG1 Y-Offset 018h W BG2HOFS BG2 X-Offset 01Ah W BG2VOFS BG2 Y-Offset 01Ch W BG3HOFS BG3 X-Offset 01Eh W BG3VOFS BG3 Y-Offset 020h W BG2PA BG2 Rotation/Scaling Parameter A (dx) 022h W BG2PB BG2 Rotation/Scaling Parameter B (dmx) 024h W BG2PC BG2 Rotation/Scaling Parameter C (dy) 026h W BG2PD BG2 Rotation/Scaling Parameter D (dmy) 028h-02Ah W BG2X BG2 Reference Point X-Coordinate 02Ch-02Eh W BG2Y BG2 Reference Point Y-Coordinate 030h W BG3PA BG3 Rotation/Scaling Parameter A (dx) 032h W BG3PB BG3 Rotation/Scaling Parameter B (dmx) 034h W BG3PC BG3 Rotation/Scaling Parameter C (dy) 036h W BG3PD BG3 Rotation/Scaling Parameter D (dmy) 038h-03Ah W BG3X BG3 Reference Point X-Coordinate 03Ch-03Eh W BG3Y BG3 Reference Point Y-Coordinate 040h W WIN0H Window 0 Horizontal Dimensions 042h W WIN1H Window 1 Horizontal Dimensions 044h W WIN0V Window 0 Vertical Dimensions 046h W WIN1V Window 1 Vertical Dimensions 048h R/W WININ Control Inside of Window(s) 04Ah R/W WINOUT Control Outside of Windows & Inside of OBJ Window 04Ch W MOSAIC Mosaic Size 04Eh - - Not used 050h R/W BLDCNT Color Special Effects Selection (formerly BLDMOD) 052h W BLDALPHA Alpha Blending Coefficients (formerly COLEV) 054h W BLDY Brightness (Fade-In/Out) Coefficient(formerly COLY) 056h-05Eh - - Not used
Sound Registers 060h R/W SOUND1CNT_L Channel 1 Sweep register (SG10_L)(NR10) 062h R/W SOUND1CNT_H Channel 1 Duty/Length/Envelope (SG10_H)(NR11, NR12) 064h R/W SOUND1CNT_X Channel 1 Frequency/Control (SG11) (NR13, NR14) 066h - - Not used - 068h R/W SOUND2CNT_L Channel 2 Duty/Length/Envelope (SG20) (NR21, NR22) 06Ah - - Not used - 06Ch R/W SOUND2CNT_H Channel 2 Frequency/Control (SG21) (NR23, NR24) 06Eh - - Not used - 070h R/W SOUND3CNT_L Channel 3 Stop/Wave RAM select (SG30_L)(NR30) 072h R/W SOUND3CNT_H Channel 3 Length/Volume (SG30_H)(NR31, NR32) 074h R/W SOUND3CNT_X Channel 3 Frequency/Control (SG31) (NR33, NR34) 076h - - Not used - 078h R/W SOUND4CNT_L Channel 4 Length/Envelope (SG40) (NR41, NR42) 07Ah - - Not used - 07Ch R/W SOUND4CNT_H Channel 4 Frequency/Control (SG41) (NR43, NR44) 07Eh - - Not used - 080h R/W SOUNDCNT_L Control Stereo/Volume/Enable (SGCNT0_L)(NR50, NR51) 082h R/W SOUNDCNT_H Control Mixing/DMA Control (SGCNT0_H) 084h R/W SOUNDCNT_X Control Sound on/off (SGCNT1) (NR52) 086h - - Not used 088h BIOS SOUNDBIAS Sound PWM Control (SG_BIAS) 08Ah-08Eh - - Not used 090h-09Eh R/W WAVE_RAM Channel 3 Wave Pattern RAM (2 banks!!) (SGWR) 0A0h-0A2h W FIFO_A Channel A FIFO, Data 0-3 (SGFIFOA) 0A4h-0A6h W FIFO_B Channel B FIFO, Data 0-3 (SGFIFOB) 0A8h-0AEh - - Not used
DMA Transfer Channels 0B0h-0B2h W DMA0SAD DMA 0 Source Address 0B4h-0B6h W DMA0DAD DMA 0 Destination Address 0B8h W DMA0CNT_L DMA 0 Word Count 0BAh R/W DMA0CNT_H DMA 0 Control 0BCh-0BEh W DMA1SAD DMA 1 Source Address 0C0h-0C2h W DMA1DAD DMA 1 Destination Address 0C4h W DMA1CNT_L DMA 1 Word Count 0C6h R/W DMA1CNT_H DMA 1 Control 0C8h-0CAh W DMA2SAD DMA 2 Source Address 0CCh-0CEh W DMA2DAD DMA 2 Destination Address 0D0h W DMA2CNT_L DMA 2 Word Count 0D2h R/W DMA2CNT_H DMA 2 Control 0D4h-0D6h W DMA3SAD DMA 3 Source Address 0D8h-0DAh W DMA3DAD DMA 3 Destination Address 0DCh W DMA3CNT_L DMA 3 Word Count 0DEh R/W DMA3CNT_H DMA 3 Control 0E0h-0FEh - - Not used
Timer Registers 100h R/W TM0CNT_L Timer 0 Counter/Reload (formerly TM0D) 102h R/W TM0CNT_H Timer 0 Control (formerly TM0CNT) 104h R/W TM1CNT_L Timer 1 Counter/Reload (formerly TM1D) 106h R/W TM1CNT_H Timer 1 Control (formerly TM1CNT) 108h R/W TM2CNT_L Timer 2 Counter/Reload (formerly TM2D) 10Ah R/W TM2CNT_H Timer 2 Control (formerly TM2CNT) 10Ch R/W TM3CNT_L Timer 3 Counter/Reload (formerly TM3D) 10Eh R/W TM3CNT_H Timer 3 Control (formerly TM3CNT) 110h-11Eh - - Not used
Serial Communication (1) 120h-122h R/W SIODATA32 SIO Data (Normal-32bit Mode) (shared with below!) 120h R/W SIOMULTI0 SIO Data 0 (Parent) (Multi-Player Mode) (SCD0) 122h R/W SIOMULTI1 SIO Data 1 (1st Child) (Multi-Player Mode) (SCD1) 124h R/W SIOMULTI2 SIO Data 2 (2nd Child) (Multi-Player Mode) (SCD2) 126h R/W SIOMULTI3 SIO Data 3 (3rd Child) (Multi-Player Mode) (SCD3) 128h R/W SIOCNT SIO Control Register (SCCNT_L) 12Ah R/W SIOMLT_SEND SIO Data (Local of Multi-Player) (shared below) 12Ah R/W SIODATA8 SIO Data (Normal-8bit and UART Mode) (SCCNT_H) 12Ch-12Eh - - Not used
Keypad Input 130h R KEYINPUT Key Status (formerly P1) 132h R/W KEYCNT Key Interrupt Control (formerly P1CNT)
Serial Communication (2) 134h R/W RCNT SIO Mode Select/General Purpose Data (formerly R) 136h - IR Ancient - Infrared Register (Prototypes only) 138h-13Eh - - Not used 140h R/W JOYCNT SIO JOY Bus Control (formerly HS_CTRL) 142h-14Eh - - Not used 150h-152h R/W JOY_RECV SIO JOY Bus Receive Data (formerly JOYRE) 154h-156h R/W JOY_TRANS SIO JOY Bus Transmit Data (formerly JOYTR) 158h R/? JOYSTAT SIO JOY Bus Receive Status (formerly JSTAT) 15Ah-1FEh - - Not used
Interrupt, Waitstate, and Power-Down Control 200h R/W IE Interrupt Enable Register 202h R/W IF Interrupt Request Flags / IRQ Acknowledge 204h R/W WAITCNT Game Pak Waitstate Control (formerly WSCNT) 206h - - Not used 208h R/W IME Interrupt Master Enable Register 20Ah-2FFh - - Not used 300h R/W HALTCNT Undocumented - Power Down Control 302h-40Fh - - Not used 410h ? ? Undocumented - Purpose Unknown ??? 0FFh 411h-7FFh - - Not used 800h-802h R/W ? Undocumented - Internal Memory Control (R/W) 804h-FFFFh - - Not used
