Overall Memory Map
General Internal Memory
- 00000000-00003FFF BIOS - System ROM (16 KBytes)
- 00004000-01FFFFFF Not used
- 02000000-0203FFFF WRAM - On-board Work RAM (External Working RAM) (256 KBytes) 2 Wait
- 02040000-02FFFFFF Not used
- 03000000-03007FFF WRAM - On-chip Work RAM (Internal Working RAM) (32 KBytes)
- 03008000-03FFFFFF Not used
- 04000000-040003FE I/O Registers
- 04000400-04FFFFFF Not used
Internal Display Memory
- 05000000-050003FF BG/OBJ Palette RAM (1 Kbyte)
- 05000400-05FFFFFF Not used
- 06000000-06017FFF VRAM - Video RAM (96 KBytes)
- 06018000-06FFFFFF Not used
- 07000000-070003FF OAM - OBJ Attributes (1 Kbyte)
- 07000400-07FFFFFF Not used
External Memory (Game Pak)
- 08000000-09FFFFFF Game Pak ROM/FlashROM (max 32MB) - Wait State 0
- 0A000000-0BFFFFFF Game Pak ROM/FlashROM (max 32MB) - Wait State 1
- 0C000000-0DFFFFFF Game Pak ROM/FlashROM (max 32MB) - Wait State 2
- 0E000000-0E00FFFF Game Pak SRAM (max 64 KBytes) - 8bit Bus width
- 0E010000-0FFFFFFF Not used
Regarding the GamePak ROM memory: the access speed of each aforementioned sections can be set individually, thus they are named Wait State 0, Wait State 1 and Wait State 2. This specifications enables the optional use of the ROM by varying the access speed.
Unused Memory Area
- 10000000-FFFFFFFF Not used (upper 4bits of address bus unused)
Default WRAM Usage
- The 256 bytes located at 03007F00h-03007FFFh in the Internal Working RAM are reserved for Interrupt vector, Interrupt Stack, and BIOS Call Stack.
- The remaining memory is free for whatever use, including the User Stack, initially located at 03007F00h.
CPU Read/Write Access Widths
| 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 X |
| Work RAM 256K | 16 | 8/16/32 | 8/16/32 | 3/3/6 XX |
| Palette RAM | 16 | 8/16/32 | 16/32 | 1/1/2 X |
| VRAM | 16 | 8/16/32 | 16/32 | 1/1/2 X |
| GamePak ROM | 16 | 8/16/32 | - | 5/5/8 XX / XXX |
| GamePak Flash | 16 | 8/16/32 | 16/32 | 5/5/8 XX / XXX |
| GamePak SRAM | 8 | 8 | 8 | 5 XX |
X - Plus 1 cycle if GBA accesses video memory at the same time.
XX - Default waitstate settings, see System Control chapter.
XXX - Separate timings for sequential, and non-sequential accesses.
Note on performance: As the GamePak bus is limited to 16 bits, executing ARM instrucions (which has 32-bit opcodes) from inside of the ROM would eventually result in a not so good performance. It’s reccomended to use THUMB instructions (16-bit each) so each opcode can be read at once.