cystev兄,因为论坛出了问题,早上所发的帖子全都没了...所以,我将你的帖子转过来!
Technical Data
CPU Modes
ARM Mode ARM7TDMI 32bit RISC CPU, 16.78MHz, 32bit opcodes (GBA)
THUMB Mode ARM7TDMI 32bit RISC CPU, 16.78MHz, 16bit opcodes (GBA)
CGB Mode Z80/8080-style 8bit CPU, 4.2MHz or 8.4MHz (CGB compatibility)
DMG Mode Z80/8080-style 8bit CPU, 4.2MHz (monochrome gameboy compatib.)
Internal Memory
BIOS ROM 16 KBytes
Work RAM 288 KBytes (32K in-chip + 256K on-board)
VRAM 96 KBytes
OAM 1 KByte (128 OBJs 3x16bit, 32 OBJ-Rotation/Scalings 4x16bit)
Palette RAM 1 KByte (256 BG colors, 256 OBJ colors)
Video
Display 240x160 pixels (2.9 inch TFT color LCD display)
BG layers 4 background layers
BG types Tile/map based, or Bitmap based
BG colors 256 colors, or 16 colors/16 palettes, or 32768 colors
OBJ colors 256 colors, or 16 colors/16 palettes
Effects Rotation/Scaling, alpha blending, fade-in/out, mosaic, window
OBJ size 12 types (in range 8x8 up to 64x64 dots)
OBJs/Screen max. 128 OBJs of any size (up to 64x64 dots each)
OBJs/Line max. 128 OBJs of 8x8 dots size (under best circumstances)
Priorities OBJ/OBJ: 0-127, OBJ/BG: 0-3, BG/BG: 0-3
Effects Rotation/Scaling, alpha blending, fade-in/out, mosaic, window
Sound
Analogue 4 channel CGB compatible
Digital 2 DMA sound channels
Output Built-in speaker, or stereo headphones
Controls
Gamepad 4 Direction Keys, 6 Buttons
Communication Ports
Serial Port Various transfer modes, 4-Player Link, Single Game Pak play
External Memory
GBA Game Pak max. 32MB ROM or flash ROM + max 64K SRAM
CGB Game Pak max. 32KB ROM + 8KB SRAM (more memory requires banking)
Power Supply
Battery Life-time approx. 15 hours
External 3.3V DC (works with somewhat 2.7V-3.3V, or maybe a bit more)
The separate CPU modes cannot be operated simultaneously. Switching is allowed between ARM and THUMB modes only (that are the two GBA modes).
This manual does not describe CGB and DMG modes, both are completely different than GBA modes, and both cannot be accessed from inside of GBA modes anyways.
Memory Map
General Internal Memory
0000:0000-0000:3FFF BIOS - System ROM (16 KBytes)
0000:4000-01FF:FFFF Not used
0200:0000-0203:FFFF WRAM - On-board Work RAM (256 KBytes) 2 Wait
0204:0000-02FF:FFFF Not used
0300:0000-0300:7FFF WRAM - In-chip Work RAM (32 KBytes)
0300:8000-03FF:FFFF Not used
0400:0000-0400:03FE I/O Registers
0400:0400-04FF:FFFF Not used
Internal Display Memory
0500:0000-0500:03FF BG/OBJ Palette RAM (1 Kbyte)
0500:0400-05FF:FFFF Not used
0600:0000-0617:FFFF VRAM - Video RAM (96 KBytes)
0618:0000-06FF:FFFF Not used
0700:0000-0700:03FF OAM - OBJ Attributes (1 Kbyte)
0700:0400-07FF:FFFF Not used
External Memory (Game Pak)
0800:0000-09FF:FFFF Game Pak ROM/FlashROM (max 32MB) - Wait State 0
0A00:0000-0BFF:FFFF Game Pak ROM/FlashROM (max 32MB) - Wait State 1
0C00:0000-0DFF:FFFF Game Pak ROM/FlashROM (max 32MB) - Wait State 2
0E00:0000-0E00:FFFF Game Pak SRAM (max 64 KBytes) - 8bit Bus width
0E01:0000-0FFF:FFFF Not used
Unused Memory Area
1000:0000-FFFF:FFFF Not used (upper 4bits of address bus unused)
Default WRAM Usage
By default, the 256 bytes at 0300:7F00h-0300:7FFFh in Work RAM are reserved for Interrupt vector, Interrupt Stack, and BIOS Call Stack. The remaining WRAM is free for whatever use (including User Stack, which is initially located at 0300:7F00h).
Address Bus Width and CPU Read/Write Access Widths
Shows the Bus-Width, supported read and write widths, and the clock cycles for 8/16/32bit accesses.
Region Bus Read Write Cycles
BIOS ROM 32 8/16/32 - 1/1/1
Work RAM 32K 32 8/16/32 8/16/32 1/1/1
I/O 32 8/16/32 8/16/32 1/1/1
OAM 32 8/16/32 16/32 1/1/1 *
Work RAM 256K 16 8/16/32 8/16/32 3/3/6 **
Palette RAM 16 8/16/32 16/32 1/1/2 *
VRAM 16 8/16/32 16/32 1/1/2 *
GamePak ROM 16 8/16/32 - 5/5/8 **/***
GamePak Flash 16 8/16/32 16/32 5/5/8 **/***
GamePak SRAM 8 8 8 5 **
Timing Notes:
* Plus 1 cycle if GBA accesses video memory at the same time.
** Default waitstate settings, see System Control chapter.
*** Separate timings for sequential, and non-sequential accesses.
One cycle equals approx. 59.59ns (ie. 16.78MHz clock).
All memory (except GamePak SRAM) can be accessed by 16bit and 32bit DMA.
GamePak Memory
Only DMA3 (and the CPU of course) may access GamePak ROM. GamePak SRAM can be accessed by the CPU only - restricted to bytewise 8bit transfers. SRAM is supposed as external WRAM expansion - not for battery-buffered data storage - for that purpose it'd be more recommended to use a Flash ROM chip somewhere located in the ROM area.
For details about configuration of GamePak Waitstates, read respective chapter.
SRAM should be accessed only through library ???
VRAM, OAM, and Palette RAM Access
These memory regions can be accessed during H-Blank or V-Blank only (unless display is disabled by Forced Blank bit in DISPCNT register).
There is an additional restriction for OAM memory: Accesses during H-Blank are allowed only if 'H-Blank Interval Free' in DISPCNT is set (which'd reduce number of display-able OBJs though).
The CPU appears to be able to access VRAM/OAM/Palette at any time, a waitstate (one clock cycle) being inserted automatically in case that the display controller was accessing memory simultaneously. (Ie. unlike as in old 8bit gameboy, the data will not get lost.)
CPU Mode Performance
Note that the GamePak ROM bus is limited to 16bits, thus executing ARM instructions (32bit opcodes) from inside of GamePak ROM would result in a not so good performance. So, it'd be more recommended to use THUMB instruction (16bit opcodes) which'd allow each opcode to be read at once.
(ARM instructions can be used at best performance by copying code from GamePak ROM into internal Work RAM)
Data Format
Even though the ARM CPU itself would allow to select between Little-Endian and Big-Endian format by using an external circuit, in the GBA no such circuit exists, and the data format is always Little-Endian. That is, when accessing 16bit or 32bit data in memory, the least significant bits are stored in the first byte (smallest address), and the most significant bits in the last byte. (Ie. same as for 80x86 and Z80 CPUs.)
I/O Map
Forward
The base address for GBA I/O ports is 04000000h - all address below are actually meant to be located 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
All further addresses at 4XXXXXXh are unused and do not contain mirrors of the I/O area, with the only exception that 800h-802h is repeated each 64K (ie. mirrored at 10800h, 20800h, etc.)
LCD Video Controller
Registers
LCD I/O Display Control
LCD I/O Interrupts and Status
LCD I/O BG Control
LCD I/O BG Scrolling
LCD I/O BG Rotation/Scaling
LCD I/O Window Feature
LCD I/O Mosaic Function
LCD I/O Color Special Effects
VRAM
LCD VRAM Overview
LCD VRAM Character Data
LCD VRAM BG Screen Data Format (BG Map)
LCD VRAM Bitmap BG Modes
Sprites
LCD OBJ - Overview
LCD OBJ - OAM Attributes
LCD OBJ - OAM Rotation/Scaling Parameters
LCD OBJ - VRAM Character (Tile) Mapping
Other
LCD Color Palettes
LCD Dimensions and Timings
LCD I/O Display Control
000h - DISPCNT - LCD Control (Read/Write)
Bit Expl.
0-2 BG Mode (0-5=Video Mode 0-5, 6-7=Prohibited)
3 Reserved for BIOS (CGB Mode - cannot be changed after startup)
4 Display Frame Select (0-1=Frame 0-1) (for BG Modes 4,5 only)
5 H-Blank Interval Free (1=Allow access to OAM during H-Blank)
6 OBJ Character VRAM Mapping (0=Two dimensional, 1=One dimensional)
7 Forced Blank (1=Allow access to VRAM,Palette,OAM)
8 Screen Display BG0 (0=Off, 1=On)
9 Screen Display BG1 (0=Off, 1=On)
10 Screen Display BG2 (0=Off, 1=On)
11 Screen Display BG3 (0=Off, 1=On)
12 Screen Display OBJ (0=Off, 1=On)
13 Window 0 Display Flag (0=Off, 1=On)
14 Window 1 Display Flag (0=Off, 1=On)
15 OBJ Window Display Flag (0=Off, 1=On)
The table summarizes the facilities of the separate BG modes (video modes).
Mode Rot/Scal Layers Size Tiles Colors Features
0 No 0123 256x256..512x515 1024 16/16..256/1 SFMABP
1 Mixed 012- (BG0,BG1 as above Mode 0, BG2 as below Mode 2)
2 Yes --23 128x128..1024x1024 256 256/1 S-MABP
3 Yes --?- 240x160 1 32768 --MABP
4 Yes --?? 240x160 2 256/1 --MABP
5 Yes --?? 160x128 2 32768 --MABP
Features: S)crolling, F)lip, M)osaic, A)lphaBlending, B)rightness, P)riority.
BG Modes 0-2 are Tile/Map-based. BG Modes 3-5 are Bitmap-based, in these modes 1 or 2 Frames (ie. bitmaps, or 'full screen tiles') exists, if two frames exist, either one can be displayed, and the other one can be redrawn in background.
Blanking Bits
Setting Forced Blank (Bit 7) causes the video controller to display white lines, and all VRAM, Palette RAM, and OAM may be accessed.
'When the internal HV synchronous counter cancels a forced blank during a display period, the display begins from the beginning, following the display of two vertical lines.' What ???
Setting H-Blank Interval Free (Bit 5) allows to access OAM during H-Blank time - using this feature reduces the number of sprites that can be displayed per line.
Display Enable Bits
By default, BG0-3 and OBJ Display Flags (Bit 8-12) are used to enable/disable BGs and OBJ. When enabeling Window 0 and/or 1 (Bit 13-14), color special effects may be used, and BG0-3 and OBJ are controlled by the window(s).
Frame Selection
In BG Modes 4 and 5 (Bitmap modes), either one of the two bitmaps/frames may be displayed (Bit 4), allowing the user to update the other (invisible) frame in background. In BG Mode 3, only one frame exists.
In BG Modes 0-2 (Tile/Map based modes), a similiar effect may be gained by altering the base address(es) of BG Map and/or BG Character data.
002h - Undocumented - Green Swap (R/W)
Normally, red green blue intensities for a group of two pixels is output as BGRbgr (uppercase for left pixel at even xloc, lowercase for right pixel at odd xloc). When the Green Swap bit is set, each pixel group is output as BgRbGr (ie. green intensity of each two pixels exchanged).
Bit Expl.
0 Green Swap (0=Normal, 1=Swap)
1-15 Not used
This feature appears to be applied to the final picture (ie. after mixing the separate BG and OBJ layers). Eventually intended for other display types (with other pin-outs). With normal GBA hardware it is just producing an interesting dirt effect.
LCD I/O Interrupts and Status
004h - DISPSTAT - General LCD Status (Read/Write)
Display status and Interrupt control. The H-Blank conditions are generated once per scanline, including for the 'hidden' scanlines during V-Blank.
Bit Expl.
0 V-Blank flag (Read only) (1=VBlank)
1 H-Blank flag (Read only) (1=HBlank)
2 V-Counter flag (Read only) (1=Match)
3 V-Blank IRQ Enable (1=Enable)
4 H-Blank IRQ Enable (1=Enable)
5 V-Counter IRQ Enable (1=Enable)
6-7 Not used
8-15 V-Count Setting (0-227)
The V-Count-Setting value is much the same as LYC of older gameboys, when its value is identical to the content of the VCOUNT register then the V-Counter flag is set (Bit 2), and (if enabled in Bit 5) an interrupt is requested.
006h - VCOUNT - Vertical Counter (Read only)
Indicates the currently drawn scanline, values in range from 160-227 indicate 'hidden' scanlines within VBlank area.
Bit Expl.
0-7 Current scanline (0-227)
8-15 Not Used
Note: This is much the same than the 'LY' register of older gameboys.
LCD I/O BG Control
008h - BG0CNT - BG0 Control (R/W) (BG Modes 0,1 only)
00Ah - BG1CNT - BG1 Control (R/W) (BG Modes 0,1 only)
00Ch - BG2CNT - BG2 Control (R/W) (BG Modes 0,1,2 only)
00Eh - BG3CNT - BG3 Control (R/W) (BG Modes 0,2 only)
Bit Expl.
0-1 BG Priority (0-3, 0=Highest)
2-3 Character Base Block (0-3, in units of 16 KBytes) (=BG Tile Data)
4-5 Not used (must be zero)
6 Mosaic (0=Disable, 1=Enable)
7 Colors/Palettes (0=16/16, 1=256/1)
8-12 Screen Base Block (0-31, in units of 2 KBytes) (=BG Map Data)
13 Display Area Overflow (0=Transparent, 1=Wraparound; BG2CNT/BG3CNT only)
14-15 Screen Size (0-3)
Internal Screen Size (dots) and size of BG Map (bytes):
Value Text Mode Rotation/Scaling Mode
0 256x256 (2K) 128x128 (256 bytes)
1 512x256 (4K) 256x256 (1K)
2 256x512 (4K) 512x512 (4K)
3 512x512 (8K) 1024x1024 (16K)
In case that some or all BGs are set to same priority then BG0 is having the highest, and BG3 the lowest priotity.
In 'Text Modes', the screen size is organized as follows: The screen consists of one or more 256x256 pixel (32x32 tiles) areas. When Size=0: only 1 area (SC0), when Size=1 or Size=2: two areas (SC0,SC1 either horizontally or vertically arranged next to each other), when Size=3: four areas (SC0,SC1 in upper row, SC2,SC3 in lower row). Whereas SC0 is defined by the normal BG Map base address (Bit 8-12 of BG#CNT), SC1 uses same address +2K, SC2 address +4K, SC3 address +6K. When the screen is scrolled it'll always wraparound.
In 'Rotation/Scaling Modes', the screen size is organized as follows, only one area (SC0) of variable size 128x128..1024x1024 pixels (16x16..128x128 tiles) exists (SC0). When the screen is rotated/scaled (or scrolled?) so that the LCD viewport reaches outside of the background/screen area, then BG may be either displayed as transparent or wraparound (Bit 13 or BG#CNT).
LCD I/O BG Scrolling
010h - BG0HOFS - BG0 X-Offset (W)
012h - BG0VOFS - BG0 Y-Offset (W)
Bit Expl.
0-8 Offset (0-511)
9-15 Not used
Specifies the coordinate of the upperleft first visible dot of BG0 background layer, ie. used to scroll the BG0 area.
014h - BG1HOFS - BG1 X-Offset (W)
016h - BG1VOFS - BG1 Y-Offset (W)
Same as above BG0HOFS and BG0VOFS for BG1 respectively.
018h - BG2HOFS - BG2 X-Offset (W)
01Ah - BG2VOFS - BG2 Y-Offset (W)
Same as above BG0HOFS and BG0VOFS for BG2 respectively.
01Ch - BG3HOFS - BG3 X-Offset (W)
01Eh - BG3VOFS - BG3 Y-Offset (W)
Same as above BG0HOFS and BG0VOFS for BG3 respectively.
The above BG scrolling registers are exclusively used in Text modes, ie. for all layers in BG Mode 0, and for the first two layers in BG mode 1.
In other BG modes (Rotation/Scaling and Bitmap modes) above registers are ignored. Instead, the screen may be scrolled by modifying the BG Rotation/Scaling Reference Point registers.
LCD I/O BG Rotation/Scaling
028h - BG2X_L - BG2 Reference Point X-Coordinate, lower 16 bit (W)
02Ah - BG2X_H - BG2 Reference Point X-Coordinate, upper 12 bit (W)
02Ch - BG2Y_L - BG2 Reference Point Y-Coordinate, lower 16 bit (W)
02Eh - BG2Y_H - BG2 Reference Point Y-Coordinate, upper 12 bit (W)
These registers are replacing the BG scrolling registers which are used for Text mode, ie. the X/Y coordinates specify the source position from inside of the BG Map/Bitmap of the pixel to be displayed at upper left of the GBA display. The normal BG scrolling registers are ignored in Rotation/Scaling and Bitmap modes.
Bit Expl.
0-7 Fractional portion (8 bits)
8-26 Integer portion (19 bits)
27 Sign (1 bit)
28-31 Not used
Because values are shifted left by eight, fractional portions may be specified in steps of 1/256 pixels (this would be relevant only if the screen is actually rotated or scaled). Normal signed 32bit values may be written to above registers (the most significant bits will be ignored and the value will be cut-down to 28bits, but this is no actual problem because signed values have set all MSBs to the same value).
Internal Reference Point Registers
The above reference points are automatically copied to internal registers during each vblank, specifying the origin for the first scanline. The internal registers are then incremented by dmx and dmy after each scanline.
Caution: Writing to a reference point register by software outside of the Vblank period does immediately copy the new value to the corresponding internal register, that means: in the current frame, the new value specifies the origin of the <current> scanline (instead of the topmost scanline).
020h - BG2PA - BG2 Rotation/Scaling Parameter A (alias dx) (W)
022h - BG2PB - BG2 Rotation/Scaling Parameter B (alias dmx) (W)
024h - BG2PC - BG2 Rotation/Scaling Parameter C (alias dy) (W)
026h - BG2PD - BG2 Rotation/Scaling Parameter D (alias dmy) (W)
Bit Expl.
0-7 Fractional portion (8 bits)
8-14 Integer portion (7 bits)
15 Sign (1 bit)
See below for details.
03Xh - BG3X_L/H, BG3Y_L/H, BG3PA-D - BG3 Rotation/Scaling Parameters
Same as above BG2 Reference Point, and Rotation/Scaling Parameters, for BG3 respectively.
dx (PA) and dy (PC)
When transforming a horizontal line, dx and dy specify the resulting gradient and magnification for that line. For example:
Horizontal line, length=100, dx=1, and dy=1. The resulting line would be drawn at 45 degrees, f(y)=1/1*x. Note that this would involve that line is magnified, the new length is SQR(100^2+100^2)=141.42. Yup, exactly - that's the old a^2 + b^2 = c^2 formula.
dmx (PB) and dmy (PD)
These values define the resulting gradient and magnification for transformation of vertical lines. However, when rotating a square area (which is surrounded by horizontal and vertical lines), then the desired result should be usually a rotated <square> area (ie. not a parallelogram, for example).
Thus, dmx and dmy must be defined in direct relationship to dx and dy, taking the example above, we'd have to set dmx=-1, and dmy=1, f(x)=-1/1*y.
Area Overflow
In result of rotation/scaling it may often happen that areas outside of the actual BG area become moved into the LCD viewport. Depending of the Area Overflow bit (BG2CNT and BG3CNT, Bit 13) these areas may be either displayed (by wrapping the BG area), or may be displayed transparent.
This works only in BG modes 1 and 2. The area overflow is ignored in Bitmap modes (BG modes 3-5), the outside of the Bitmaps is always transparent.
--- more details and confusing or helpful formulas ---
The following parameters are required for Rotation/Scaling
Rotation Center X and Y Coordinates (x0,y0)
Rotation Angle (alpha)
Magnification X and Y Values (xMag,yMag)
The display is rotated by 'alpha' degrees around the center.
The displayed picture is magnified by 'xMag' along x-Axis (Y=y0) and 'yMag' along y-Axis (X=x0).
Calculating Rotation/Scaling Parameters A-D
A = Cos (alpha) / xMag ;distance moved in direction x, same line
B = Sin (alpha) / xMag ;distance moved in direction x, next line
C = Sin (alpha) / yMag ;distance moved in direction y, same line
D = Cos (alpha) / yMag ;distance moved in direction y, next line
Calculating the position of a rotated/scaled dot
Using the following expressions,
x0,y0 Rotation Center
x1,y1 Old Position of a pixel (before rotation/scaling)
x2,y2 New position of above pixel (after rotation scaling)
A,B,C,D BG2PA-BG2PD Parameters (as calculated above)
the following formula can be used to calculate x2,y2:
x2 = A(x1-x0) + B(y1-y0) + x0
y2 = C(x1-x0) + D(y1-y0) + y0
LCD I/O Window Feature
The Window Feature may be used to split the screen into four regions. The BG0-3,OBJ layers and Color Special Effects can be separately enabled or disabled in each of these regions.
The DISPCNT Register
DISPCNT Bits 13-15 are used to enable Window 0, Window 1, and/or OBJ Window regions, if any of these regions is enabled then the 'Outside of Windows' region is automatically enabled, too.
DISPCNT Bits 8-12 are kept used as master enable bits for the BG0-3,OBJ layers, a layer is displayed only if both DISPCNT and WININ/OUT enable bits are set.
040h - WIN0H - Window 0 Horizontal Dimensions (W)
042h - WIN1H - Window 1 Horizontal Dimensions (W)
Bit Expl.
0-7 X2, Rightmost coordinate of window, plus 1
8-15 X1, Leftmost coordinate of window
044h - WIN0V - Window 0 Vertical Dimensions (W)
046h - WIN1V - Window 1 Vertical Dimensions (W)
Bit Expl.
0-7 Y2, Bottom-most coordinate of window, plus 1
8-15 Y1, Top-most coordinate of window
048h - WININ - Control of Inside of Window(s) (R/W)
Bit Expl.
0-3 Window 0 BG0-BG3 Enable Bits (0=No Display, 1=Display)
4 Window 0 OBJ Enable Bit (0=No Display, 1=Display)
5 Window 0 Color Special Effect (0=Disable, 1=Enable)
6-7 Not used
8-11 Window 1 BG0-BG3 Enable Bits (0=No Display, 1=Display)
12 Window 1 OBJ Enable Bit (0=No Display, 1=Display)
13 Window 1 Color Special Effect (0=Disable, 1=Enable)
14-15 Not used
04Ah - WINOUT - Control of Outside of Windows & Inside of OBJ Window (R/W)
Bit Expl.
0-3 Outside BG0-BG3 Enable Bits (0=No Display, 1=Display)
4 Outside OBJ Enable Bit (0=No Display, 1=Display)
5 Outside Color Special Effect (0=Disable, 1=Enable)
6-7 Not used
8-11 OBJ Window BG0-BG3 Enable Bits (0=No Display, 1=Display)
12 OBJ Window OBJ Enable Bit (0=No Display, 1=Display)
13 OBJ Window Color Special Effect (0=Disable, 1=Enable)
14-15 Not used
The OBJ Window
The dimension of the OBJ Window is specified by OBJs which are having the 'OBJ Mode' attribute being set to 'OBJ Window'. Any non-transparent dots of any such OBJs are marked as OBJ Window area. The OBJ itself is not displayed.
The color, palette, and display priority of these OBJs are ignored. Both DISPCNT Bits 12 and 15 must be set when defining OBJ Window region(s).
Window Priority
In case that more than one window is enabled, and that these windows do overlap, Window 0 is having highest priority, Window 1 medium, and Obj Window lowest priority. Outside of Window is having zero priority, it is used for all dots which are not inside of any window region.
LCD I/O Mosaic Function
04Ch - MOSAIC - Mosaic Size (W)
The Mosaic function can be separately enabled/disabled for BG0-BG3 by BG0CNT-BG3CNT Registers, as well as for each OBJ0-127 by OBJ attributes in OAM memory. Also, setting all of the bits below to zero effectively disables the mosaic function.
Bit Expl.
0-3 BG Mosaic H-Size (minus 1)
4-7 BG Mosaic V-Size (minus 1)
8-11 OBJ Mosaic H-Size (minus 1)
12-15 OBJ Mosaic V-Size (minus 1)
Example: When setting H-Size to 5, then pixels 0-5 of each display row are colorized as pixel 0, pixels 6-11 as pixel 6, pixels 12-17 as pixel 12, and so on.
Normally, a 'mosaic-pixel' is colorized by the color of the upperleft covered pixel. In many cases it might be more desireful to use the color of the pixel in the center of the covered area - this effect may be gained by scrolling the background (or by adjusting the OBJ position, as far as upper/left rows/columns of OBJ are transparent).
LCD I/O Color Special Effects
Two types of Special Effects are supported: Alpha Blending (Semi-Transparency) allows to combine colors of two selected surfaces. Brightness Increase/Decrease adjust the brightness of the selected surface.
050h - BLDCNT (formerly BLDMOD) - Color Special Effects Selection (R/W)
Bit Expl.
0 BG0 1st Target Pixel (Background 0)
1 BG1 1st Target Pixel (Background 1)
2 BG2 1st Target Pixel (Background 2)
3 BG3 1st Target Pixel (Background 3)
4 OBJ 1st Target Pixel (Top-most OBJ pixel)
5 BD 1st Target Pixel (Backdrop)
6-7 Color Special Effect (0-3, see below)
0 = None (Special effects disabled)
1 = Alpha Blending (1st+2nd Target mixed)
2 = Brightness Increase (1st Target becomes whiter)
3 = Brightness Decrease (1st Target becomes blacker)
8 BG0 2nd Target Pixel (Background 0)
9 BG1 2nd Target Pixel (Background 1)
10 BG2 2nd Target Pixel (Background 2)
11 BG3 2nd Target Pixel (Background 3)
12 OBJ 2nd Target Pixel (Top-most OBJ pixel)
13 BD 2nd Target Pixel (Backdrop)
14-15 Not used
Selects the 1st Target layer(s) for special effects. For Alpha Blenging/Semi-Transparency, it does also select the 2nd Target layer(s), which should have next lower display priority as the 1st Target.
However, any combinations are possible, including that all layers may be selected as both 1st+2nd target, in that case the top-most pixel will be used as 1st target, and the next lower pixel as 2nd target.
052h - BLDALPHA (formerly COLEV) - Alpha Blending Coefficients (W)
Used for Color Special Effects Mode 1, and for Semi-Transparent OBJs.
Bit Expl.
0-4 EVA Coefficient (1st Target) (0..16 = 0/16..16/16, 17..31=16/16)
5-7 Not used
8-12 EVB Coefficient (2nd Target) (0..16 = 0/16..16/16, 17..31=16/16)
13-15 Not used
For this effect, the top-most non-transparent pixel must be selected as 1st Target, and the next-lower non-transparent pixel must be selected as 2nd Target, if so - and only if so, then color intensities of 1st and 2nd Target are mixed together by using the parameters in BLDALPHA register, for each pixel each R, G, B intensities are calculated separately:
I = MIN ( 31, I1st*EVA + I2nd*EVB )
Otherwise - for example, if only one target exists, or if a non-transparent non-2nd-target pixel is moved between the two targets, or if 2nd target has higher display priority than 1st target - then only the-most pixel is displayed (at normal intensity, regardless of BLDALPHA).
054h - BLDY (formerly COLY) - Brightness (Fade-In/Out) Coefficient (W)
Used for Color Special Effects Modes 2 and 3.
Bit Expl.
0-4 EVY Coefficient (Brightness) (0..16 = 0/16..16/16, 17..31=16/16)
5-15 Not used
For each pixel each R, G, B intensities are calculated separately:
I = I1st + (31-I1st)*EVY ;For Brightness Increase
I = I1st - (I1st)*EVY ;For Brightness Decrease
The color intensities of any selected 1st target surface(s) are increased or decreased by using the parameter in BLDY register.
Semi-Transparent OBJs
OBJs that are defined as 'Semi-Transparent' in OAM memory are always selected as 1st Target (regardless of BLDCNT Bit 4), and are always using Alpha Blending mode (regardless of BLDCNT Bit 6-7).
The BLDCNT register may be used to perform Brightness effects on the OBJ (and/or other BG/BD layers). However, if a semi-transparent OBJ pixel does overlap a 2nd target pixel, then semi-transparency becomes priority, and the brightness effect will not take place (neither on 1st, nor 2nd target).
The OBJ Layer
Before special effects are applied, the display controller computes the OBJ priority ordering, and isolates the top-most OBJ pixel. In result, only the top-most OBJ pixel is recursed at the time when processing special effects. Ie. alpha blending and semi-transparency can be used for OBJ-to-BG or BG-to-OBJ , but not for OBJ-to-OBJ.
LCD VRAM Overview
The GBA contains 96 Kbytes VRAM built-in, located at address 06000000-06017FFF, depending on the BG Mode used as follows:
BG Mode 0,1,2 (Tile/Map based Modes)
06000000-0600FFFF 64 KBytes shared for BG Map and Tiles
06010000-06017FFF 32 KBytes OBJ Tiles
The shared 64K area will be split into BG Map area (max. 32K) and BG Tiles area (min 32K), the respective addresses for Map and Tile areas are set up by BG0CNT-BG3CNT registers. The Map address may be specified in units of 2K (steps of 800h), the Tile address in units of 16K (steps of 4000h).
BG Mode 3 (Bitmap based Mode for still images)
06000000-06013FFF 80 KBytes Frame 0 buffer (only 75K actually used)
06014000-06017FFF 16 KBytes OBJ Tiles
BG Mode 4,5 (Bitmap based Modes)
06000000-06009FFF 40 KBytes Frame 0 buffer (only 37.5K used in Mode 4)
0600A000-06013FFF 40 KBytes Frame 1 buffer (only 37.5K used in Mode 4)
06014000-06017FFF 16 KBytes OBJ Tiles
Note
Additionally to the above VRAM, the GBA also contains 1 KByte Palette RAM (at 05000000h) and 1 KByte OAM (at 07000000h) which are both used by the display controller as well.
LCD VRAM Character Data
Each character (tile) consists of 8x8 dots (64 dots in total). The color depth may be either 4bit or 8bit (see BG0CNT-BG3CNT).
4bit depth (16 colors, 16 palettes)
Each tile occupies 32 bytes of memory, the first 4 bytes for the topmost row of the tile, and so on. Each byte representing two dots, the lower 4 bits define the color for the left (!) dot, the upper 4 bits the color for the right dot.
8bit depth (256 colors, 1 palette)
Each tile occupies 64 bytes of memory, the first 8 bytes for the topmost row of the tile, and so on. Each byte selects the palette entry for each dot.
LCD VRAM BG Screen Data Format (BG Map)
The display background consists of 8x8 dot tiles, the arrangement of these tiles is specified by the BG Screen Data (BG Map). The separate entries in this map are as follows:
Text BG Screen (2 bytes per entry)
Specifies the tile number and attributes. Note that BG tile numbers are always specified in steps of 1 (unlike OBJ tile numbers which are using steps of two in 256 color/1 palette mode).
Bit Expl.
0-9 Tile Number (0-1023) (a bit less in 256 color mode, because
there'd be otherwise no room for the bg map)
10 Horizontal Flip (0=Normal, 1=Mirrored)
11 Vertical Flip (0=Normal, 1=Mirrored)
12-15 Palette Number (0-15) (Not used in 256 color/1 palette mode)
A Text BG Map always consists of 32x32 entries (256x256 pixels), 400h entries = 800h bytes. However, depending on the BG Size, one, two, or four of these Maps may be used together, allowing to create backgrounds of 256x256, 512x256, 256x512, or 512x512 pixels, if so, the first map (SC0) is located at base+0, the next map (SC1) at base+800h, and so on.
Rotation/Scaling BG Screen (1 byte per entry)
In this mode, only 256 tiles can be used. There are no x/y-flip attributes, the color depth is always 256 colors/1 palette.
Bit Expl.
0-7 Tile Number (0-255)
The dimensions of Rotation/Scaling BG Maps depend on the BG size. For size 0-3 that are: 16x16 tiles (128x128 pixels), 32x32 tiles (256x256 pixels), 64x64 tiles (512x512 pixels), or 128x128 tiles (1024x1024 pixels).
The size and VRAM base address of the separate BG maps for BG0-3 are set up by BG0CNT-BG3CNT registers.
LCD VRAM Bitmap BG Modes
In BG Modes 3-5 the background is defined in form of a bitmap (unlike as for Tile/Map based BG modes). Bitmaps are implemented as BG2, with Rotation/Scaling support. As bitmap modes are occupying 80KBytes of BG memory, only 16KBytes of VRAM can be used for OBJ tiles.
BG Mode 3 - 240x160 pixels, 32768 colors
Two bytes are associated to each pixel, directly defining one of the 32768 colors (without using palette data, and thus not supporting a 'transparent' BG color).
Bit Expl.
0-4 Red Intensity (0-31)
5-9 Green Intensity (0-31)
10-14 Blue Intensity (0-31)
15 Not used
The first 480 bytes define the topmost line, the next 480 the next line, and so on. The background occupies 75 KBytes (06000000-06012BFF), most of the 80 Kbytes BG area, not allowing to redraw an invisble second frame in background, so this mode is mostly recommended for still images only.
BG Mode 4 - 240x160 pixels, 256 colors (out of 32768 colors)
One byte is associated to each pixel, selecting one of the 256 palette entries. Color 0 (backdrop) is transparent, and OBJs may be displayed behind the bitmap.
The first 240 bytes define the topmost line, the next 240 the next line, and so on. The background occupies 37.5 KBytes, allowing two frames to be used (06000000-060095FF for Frame 0, and 0600A000-060135FF for Frame 1).
BG Mode 5 - 160x128 pixels, 32768 colors
Colors are defined as for Mode 3 (see above), but horizontal and vertical size are cut down to 160x128 pixels only - smaller than the physical dimensions of the LCD screen.
The background occupies exactly 40 KBytes, so that BG VRAM may be split into two frames (06000000-06009FFF for Frame 0, and 0600A000-06013FFF for Frame 1).
In BG modes 4,5, one Frame may be displayed (selected by DISPCNT Bit 4), the other Frame is invisible and may be redrawn in background.
LCD OBJ - Overview
General
Objects (OBJs) are moveable sprites. Up to 128 OBJs (of any size, up to 64x64 dots each) can be displayed per screen, and under best circumstances up to 128 OBJs (of small 8x8 dots size) can be displayed per horizontal display line.
Maximum Number of Sprites per Line
The total available OBJ rendering cycles per line are
1210 (=304*4-6) If 'H-Blank Interval Free' bit in DISPCNT register is 0
954 (=240*4-6) If 'H-Blank Interval Free' bit in DISPCNT register is 1
The required rendering cycles are (depending on horizontal OBJ size)
Cycles per Screen Pixels OBJ Type OBJ Type Screen Pixel Range
8 cycles per 8 pixels Normal OBJs 8..64 pixels
26 cycles per 8 pixels Rotation/Scaling OBJs 8..64 pixels (area clipped)
26 cycles per 8 pixels Rotation/Scaling OBJs 16..128 pixels (double size)
Caution:
The maximum number of OBJs per line is also affected by undisplayed (offscreen) OBJs which are having higher priority than displayed OBJs.
To avoid this, move displayed OBJs to the begin of OAM memory (ie. OBJ0 has highest priority, OBJ127 lowest).
Otherwise (in case that the program logic expects OBJs at fixed positions in OAM) at least take care to set the OBJ size of undisplayed OBJs to 8x8 with Rotation/Scaling disabled (this reduces the overload).
Does the above also apply for VERTICALLY OFFSCREEN (or VERTICALLY not on CURRENT LINE) sprites ???
VRAM - Character Data
OBJs are always combined of one or more 8x8 pixel Tiles (much like BG Tiles in BG Modes 0-2). However, OBJ Tiles are stored in a separate area in VRAM: 06100000-0617FFFF (32 KBytes) in BG Mode 0-2, or 06140000-0617FFFF (16 KBytes) in BG Mode 3-5.
Depending on the size of the above area (16K or 32K), and on the OBJ color depth (4bit or 8bit), 256-1024 8x8 dots OBJ Tiles can be defined.
OAM - Object Attribute Memory
This memory area contains Attributes which specify position, size, color depth, etc. appearance for each of the 128 OBJs. Additionally, it contains 32 OBJ Rotation/Scaling Parameter groups. OAM is located at 0700:0000-0700:03FF (sized 1 KByte).
LCD OBJ - OAM Attributes
OBJ Attributes
There are 128 entries in OAM for each OBJ0-OBJ127. Each entry consists of 6 bytes (three 16bit Attributes). Attributes for OBJ0 are located at 0700:0000, for OBJ1 at 0700:0008, OBJ2 at 0700:0010, and so on.
As you can see, there are blank spaces at 0700:0006, 0700:000E, 0700:0016, etc. - these 16bit values are used for OBJ Rotation/Scaling (as described in the next chapter) - they are not directly related to the separate OBJs.
OBJ Attribute 0 (R/W)
Bit Expl.
0-7 Y-Coordinate (0-255)
8 Rotation/Scaling Flag (0=Off, 1=On)
When Rotation/Scaling used (Attribute 0, bit 8 set):
9 Double-Size Flag (0=Normal, 1=Double)
When Rotation/Scaling not used (Attribute 0, bit 8 cleared):
9 OBJ Disable (0=Normal, 1=Not displayed)
10-11 OBJ Mode (0=Normal, 1=Semi-Transparent, 2=OBJ Window, 3=Prohibited)
12 OBJ Mosaic (0=Off, 1=On)
13 Colors/Palettes (0=16/16, 1=256/1)
14-15 OBJ Shape (0=Square,1=Horizontal,2=Vertical,3=Prohibited)
Caution: A very large OBJ (of 128 pixels vertically, ie. a 64 pixels OBJ in a Double Size area) located at Y>128 will be treated as at Y>-128, the OBJ is then displayed parts offscreen at the TOP of the display, it is then NOT displayed at the bottom.
OBJ Attribute 1 (R/W)
Bit Expl.
0-8 X-Coordinate (0-511)
When Rotation/Scaling used (Attribute 0, bit 8 set):
9-13 Rotation/Scaling Parameter Selection (0-31)
(Selects one of the 32 Rotation/Scaling Parameters that
can be defined in OAM, for details read next chapter.)
When Rotation/Scaling not used (Attribute 0, bit 8 cleared):
9-11 Not used
12 Horizontal Flip (0=Normal, 1=Mirrored)
13 Vertical Flip (0=Normal, 1=Mirrored)
14-15 OBJ Size (0..3, depends on OBJ Shape, see Attr 0)
Size Square Horizontal Vertical
0 8x8 16x8 8x16
1 16x16 32x8 8x32
2 32x32 32x16 16x32
3 64x64 64x32 32x64
OBJ Attribute 2 (R/W)
Bit Expl.
0-9 Character Name (0-1023=Tile Number)
10-11 Priority relative to BG (0-3; 0=Highest)
12-15 Palette Number (0-15) (Not used in 256 color/1 palette mode)
Notes:
OBJ Mode
The OBJ Mode may be Normal, Semi-Transparent, or OBJ Window.
Semi-Transparent means that the OBJ is used as 'Alpha Blending 1st Target' (regardless of BLDCNT register, for details see chapter about Color Special Effects).
OBJ Window means that the OBJ is not displayed, instead, dots with non-zero color are used as mask for the OBJ Window, see DISPCNT and WINOUT for details.
OBJ Tile Number
There are two situations which may divide the amount of available tiles by two (by four if both situations apply):
1. When using the 256 Colors/1 Palette mode, only each second tile may be used, the lower bit of the tile number should be zero (in 2-dimensional mapping mode, the bit is completely ignored).
2. When using BG Mode 3-5 (Bitmap Modes), only tile numbers 512-1023 may be used. That is because lower 16K of OBJ memory are used for BG. Attempts to use tiles 0-511 are ignored (not displayed).
Priority
In case that the 'Priority relative to BG' is the same than the priority of one of the background layers, then the OBJ becomes higher priority and is displayed on top of that BG layer.
Caution: Take care not to mess up BG Priority and OBJ priority. For example, the following would cause garbage to be displayed:
OBJ No. 0 with Priority relative to BG=1 ;hi OBJ prio, lo BG prio
OBJ No. 1 with Priority relative to BG=0 ;lo OBJ prio, hi BG prio
That is, OBJ0 is always having priority above OBJ1-127, so assigning a lower BG Priority to OBJ0 than for OBJ1-127 would be a bad idea.
LCD OBJ - OAM Rotation/Scaling Parameters
As described in the previous chapter, there are blank spaces between each of the 128 OBJ Attribute Fields in OAM memory. These 128 16bit gaps are used to store OBJ Rotation/Scaling Parameters.
Location of Rotation/Scaling Parameters in OAM
Four 16bit parameters (PA,PB,PC,PD) are required to define a complete group of Rotation/Scaling data. These are spread across OAM as such:
1st Group - PA=0700:0006, PB=0700:000E, PC=0700:0016, PD=0700:001E
2nd Group - PA=0700:0026, PB=0700:002E, PC=0700:0036, PD=0700:003E
etc.
By using all blank space (128 x 16bit), up to 32 of these groups (4 x 16bit each) can be defined in OAM.
OBJ Rotation/Scaling PA,PB,PC,PD Parameters (R/W)
Each OBJ that uses Rotation/Scaling may select between any of the above 32 parameter groups. For details, refer to the previous chapter about OBJ Attributes.
The meaning of the separate PA,PB,PC,PD values is identical as for BG, for details read the chapter about BG Rotation/Scaling.
OBJ Reference Point & Rotation Center
The OBJ Reference Point is the upper left of the OBJ, ie. OBJ X/Y coordinates: X+0, Y+0.
The OBJ Rotation Center is always (or should be usually?) in the middle of the object, ie. for a 8x32 pixel OBJ, this would be at the OBJ X/Y coordinates: X+4, and Y+16.
OBJ Double-Size Bit (for OBJs that use Rotation/Scaling)
When Double-Size is zero: The sprite is rotated, and then display inside of the normal-sized (not rotated) rectangular area - the edges of the rotated sprite will become invisible if they reach outside of that area.
When Double-Size is set: The sprite is rotated, and then display inside of the double-sized (not rotated) rectangular area - this ensures that the edges of the rotated sprite remain visible even if they would reach outside of the normal-sized area. (Except that, for example, rotating a 8x32 pixel sprite by 90 degrees would still cut off parts of the sprite as the double-size area isn't large enough.)
LCD OBJ - VRAM Character (Tile) Mapping
Each OBJ tile consists of 8x8 dots, however, bigger OBJs can be displayed by combining several 8x8 tiles. The horizontal and vertical size for each OBJ may be separately defined in OAM, possible H/V sizes are 8,16,32,64 dots - allowing 'square' OBJs to be used (such like 8x8, 16x16, etc) as well as 'rectangular' OBJs (such like 8x32, 64x16, etc.)
When displaying an OBJ that contains of more than one 8x8 tile, one of the following two mapping modes can be used. In either case, the tile number of the upperleft tile must be specified in OAM memory.
Two Dimensional Character Mapping (DISPCNT Bit 6 cleared)
This mapping mode assumes that the 1024 OBJ tiles are arranged as a matrix of 32x32 tiles / 256x256 pixels (In 256 color mode: 16x32 tiles / 128x256 pixels). Ie. the upper row of this matrix contains tiles 00h-1Fh, the next row tiles 20h-3Fh, and so on.
For example, when displaying a 16x16 pixel OBJ, with tile number set to 04h; The upper row of the OBJ will consist of tile 04h and 05h, the next row of 24h and 25h. (In 256 color mode: 04h and 06h, 24h and 26h.)
One Dimensional Character Mapping (DISPCNT Bit 6 set)
In this mode, tiles are mapped each after each other from 00h-3FFh.
Using the same example as above, the upper row of the OBJ will consist of tile 04h and 05h, the next row of tile 06h and 07h. (In 256 color mode: 04h and 06h, 08h and 0Ah.)
LCD Color Palettes
Color Palette RAM
BG and OBJ palettes are using separate memory regions:
05000000-050001FF - BG Palette RAM (512 bytes, 256 colors)
05000200-050003FF - OBJ Palette RAM (512 bytes, 256 colors)
Each BG and OBJ palette RAM may be either split into 16 palettes with 16 colors each, or may be used as a single palette with 256 colors.
Note that some OBJs may access palette RAM in 16 color mode, while other OBJs may use 256 color mode at the same time. Same for BG0-BG3 layers.
Transparent Colors
Color 0 of all BG and OBJ palettes is transparent. Even though palettes are described as 16 (256) color palettes, only 15 (255) colors are actually visible.
Backdrop Color
Color 0 of BG Palette 0 is used as backdrop color. This color is displayed if an area of the screen is not covered by any non-transparent BG or OBJ dots.
Color Definitions
Each color occupies two bytes (same as for 32768 color BG modes):
Bit Expl.
0-4 Red Intensity (0-31)
5-9 Green Intensity (0-31)
10-14 Blue Intensity (0-31)
15 Not used
Intensities
Under normal circumstances (light source/viewing angle), the intensities 0-14 are practically all black, and only intensities 15-31 are resulting in visible medium..bright colors.
Note: The intensity problem appears in the 8bit CGB 'compatibilty' mode either. The original CGB display produced the opposite effect: Intensities 0-14 resulted in dark..medium colors, and intensities 15-31 resulted in bright colors. Any 'medium' colors of CGB games will appear invisible/black on GBA hardware, and only very bright colors will be visible.
LCD Dimensions and Timings
Horizontal Dimensions
The drawing time for each dot is 4 CPU cycles.
Visible 240 dots, 57.221 us, 960 cycles - 78% of h-time
H-Blanking 68 dots, 16.212 us, 272 cycles - 22% of h-time
Total 308 dots, 73.433 us, 1232 cycles - ca. 13.620 kHz
VRAM and Palette RAM may be accessed during H-Blanking. OAM can accessed only if 'H-Blank Interval Free' bit in DISPCNT register is set.
Vertical Dimensions
Visible (*) 160 lines, 11.749 ms, 197120 cycles - 70% of v-time
V-Blanking 68 lines, 4.994 ms, 83776 cycles - 30% of v-time
Total 228 lines, 16.743 ms, 280896 cycles - ca. 59.737 Hz
All VRAM, OAM, and Palette RAM may be accessed during V-Blanking.
Note that no H-Blank interrups are generated within V-Blank period.
System Clock
The system clock is 16.78MHz (16*1024*1024 Hz), one cycle is thus approx. 59.59ns.
(*) Even though vertical screen size is 160 lines, the upper 8 lines are not <really> visible, these lines are covered by a shadow when holding the GBA orientated towards a light source, the lines are effectively black - and should not be used to display important information.
Sound Controller
The GBA supplies four 'analogue' sound channels for Tone and Noise (mostly compatible to CGB sound), as well as two 'digital' sound channels (which can be used to replay 8bit DMA sample data).
Sound Channel 1 - Tone & Sweep
Sound Channel 2 - Tone
Sound Channel 3 - Wave Output
Sound Channel 4 - Noise
Sound Channel A and B - DMA Sound
Sound Control Registers
Comparision of CGB and GBA Sound
The GBA includes only a single (mono) speaker built-in, each channel may be output to either left and/or right channels by using the external line-out connector (for stereo headphones, etc).
Sound Channel 1 - Tone & Sweep
060h - SOUND1CNT_L (formerly SG10_L) (NR10) - Channel 1 Sweep register (R/W)
Bit Expl.
0-2 R/W Number of sweep shift (n=0-7)
3 R/W Sweep Frequency Direction (0=Increase, 1=Decrease)
4-6 R/W Sweep Time; units of 7.8ms (0-7, min=7.8ms, max=54.7ms)
7-15 - Not used
Sweep is disabled by setting Sweep Time to zero, if so, the direction bit should be set.
The change of frequency (NR13,NR14) at each shift is calculated by the following formula where X(0) is initial freq & X(t-1) is last freq:
X(t) = X(t-1) +/- X(t-1)/2^n
062h - SOUND1CNT_L (SG10_H) (NR11, NR12) - Channel 1 Duty/Len/Envelope (R/W)
Bit Expl.
0-5 W Sound length; units of (64-n)/256s (0-63)
6-7 R/W Wave Pattern Duty (0-3, see below)
8-10 R/W Envelope Step-Time; units of n/64s (1-7, 0=No Envelope)
11 R/W Envelope Direction (0=Decrease, 1=Increase)
12-15 R/W Initial Volume of envelope (1-15, 0=No Sound)
Wave Duty:
0: 12.5% ( -_______-_______-_______ )
1: 25% ( --______--______--______ )
2: 50% ( ----____----____----____ ) (normal)
3: 75% ( ------__------__------__ )
The Length value is used only if Bit 6 in NR14 is set.
064h - SOUND1CNT_X (SG11) (NR13, NR14) - Channel 1 Frequency/Control (R/W)
Bit Expl.
0-10 W Frequency; 131072/(2048-n)Hz (0-2047)
11-13 - Not used
14 R/W Length Flag (1=Stop output when length in NR11 expires)
15 W Initial (1=Restart Sound)
Sound Channel 2 - Tone
This sound channel works exactly as channel 1, except that it doesn't have a Tone Envelope/Sweep Register.
066h - Not used
068h - SOUND2CNT_L (SG20) (NR21, NR22) - Channel 2 Duty/Length/Envelope (R/W)
06Ah - Not used
06Ch - SOUND2CNT_H (SG21) (NR23, NR24) - Channel 2 Frequency/Control (R/W)
06Eh - Not used
For details, refer to channel 1 description.
Sound Channel 3 - Wave Output
This channel can be used to output digital sound, the length of the sample buffer (Wave RAM) can be either 32 or 64 digits (4bit samples). This sound channel can be also used to output normal tones when initializing the Wave RAM by a square wave. This channel doesn't have a volume envelope register.
070h - SOUND3CNT_L (SG30_L) (NR30) - Channel 3 Stop/Wave RAM select (R/W)
Bit Expl.
0-4 - Not used
5 R/W Wave RAM Bank Number (0-1, see below)
6 R/W Wave RAM Dimension (0=One bank/32 digits, 1=Two banks/64 digits)
7 R/W Sound Channel 3 Off (0=Stop, 1=Playback)
8-15 - Not used
The currently selected Bank Number (Bit 5) will be played back, while reading/writing to/from wave RAM will address the other (not selected) bank. When dimension is set to two banks, output will start by replaying the currently selected bank.
072h - SOUND3CNT_H (SG30_H) (NR31, NR32) - Channel 3 Length/Volume (R/W)
Bit Expl.
0-7 W Sound length; units of (256-n)/256s (0-255)
8-12 - Not used.
13-14 R/W Sound Volume (0=Mute/Zero, 1=100%, 2=50%, 3=25%)
15 R/W Force Volume (0=Use above, 1=Force 75% regardless of above)
The Length value is used only if Bit 6 in NR34 is set.
074h - SOUND3CNT_X (SG31) (NR33, NR34) - Channel 3 Frequency/Control (R/W)
Bit Expl.
0-10 W Frequency; 131072/(2048-n) Hz (0-2047)
11-13 - Not used
14 R/W Length Flag (1=Stop output when length in NR31 expires)
15 W Initial (1=Restart Sound)
The above frequency is meant to be the sample rate per digit in wave RAM. The repeat rate for 32 digit wave RAM would be thus above frequency divided by 32. (Divided by 64 for 64 digit wave RAM).
090h - WAVE_RAM0_L (SGWR0_L) - Channel 3 Wave Pattern RAM (W/R)
092h - WAVE_RAM0_H (SGWR0_H) - Channel 3 Wave Pattern RAM (W/R)
094h - WAVE_RAM1_L (SGWR1_L) - Channel 3 Wave Pattern RAM (W/R)
096h - WAVE_RAM1_H (SGWR1_H) - Channel 3 Wave Pattern RAM (W/R)
098h - WAVE_RAM2_L (SGWR2_L) - Channel 3 Wave Pattern RAM (W/R)
09Ah - WAVE_RAM2_H (SGWR2_H) - Channel 3 Wave Pattern RAM (W/R)
09Ch - WAVE_RAM3_L (SGWR3_L) - Channel 3 Wave Pattern RAM (W/R)
09Eh - WAVE_RAM3_H (SGWR3_H) - Channel 3 Wave Pattern RAM (W/R)
This area contains 16 bytes (32 x 4bits) Wave Pattern data which is output by channel 3. Data is played back ordered as follows: MSBs of 1st byte, followed by LSBs of 1st byte, followed by MSBs of 2nd byte, and so on - this results in a confusing ordering when filling Wave RAM in units of 16bit data - ie. samples would be then located in Bits 4-7, 0-3, 12-15, 8-11.
In the GBA, two Wave Patterns exists (each 32 x 4bits), either one may be played (as selected in NR30 register), the other bank may be accessed by the users. After all 32 samples have been played, output of the same bank (or other bank, as specified in NR30) will be automatically restarted.
Internally, Wave RAM is a giant shift-register, there is no pointer which is addressing the currently played digit. Instead, the entire 128 bits are shifted, and the 4 least significant bits are output.
Thus, when reading from Wave RAM, data might have changed its postition. And, when writing to Wave RAM all data should be updated (it'd be no good idea to assume that old data is still located at the same position where it has been written to previously).
Sound Channel 4 - Noise
This channel is used to output white noise. This is done by randomly switching the amplitude between high and low at a given frequency. Depending on the frequency the noise will appear 'harder' or 'softer'.
It is also possible to influence the function of the random generator, so the that the output becomes more regular, resulting in a limited ability to output Tone instead of Noise.
076h - Not used
078h - SOUND4CNT_L (SG40) (NR41, NR42) - Channel 4 Length/Envelope (R/W)
Bit Expl.
0-5 W Sound length; units of (64-n)/256s (0-63)
6-7 - Not used
8-10 R/W Envelope Step-Time; units of n/64s (1-7, 0=No Envelope)
11 R/W Envelope Direction (0=Decrease, 1=Increase)
12-15 R/W Initial Volume of envelope (1-15, 0=No Sound)
The Length value is used only if Bit 6 in NR44 is set.
07Ah - Not used
07Ch - SOUND4CNT_H (SG41) (NR43, NR44) - Channel 4 Frequency/Control (R/W)
The amplitude is randomly switched between high and low at the given frequency. A higher frequency will make the noise to appear 'softer'.< |
|小黑屋|手机版|Archiver|Nw壬天堂世界
( 京ICP备05022083号-1 京公网安备11010202001397号 )
发表于 2004-11-29 15:58:41
提升卡
变色卡
显身卡