.NDS File Format – Memory map

Nintendo DS ROM image

The two processors of the DS do not see the same memory. The ARM9 and the ARM7 share the main RAM and, in part, the shared WRAM; each has its own I/O registers and its own other memories. The explorer labels the starts of these ranges and the registers below in the disassembly of each program. Facts on this page are from GBATEK (“DS Memory Maps” and “DS I/O Maps”).

ARM9

RangeNameWhat is there
0x00000000–0x00007FFFInstruction TCM32 KiB, fixed; mirrorable to $01000000
0x02000000–0x023FFFFFMain RAM4 MiB, shared with the ARM7
0x027C0000–0x027C3FFFData TCM16 KiB, movable; the default base is $027C0000
0x03000000–0x03007FFFShared WRAM0, 16 or 32 KiB, allocated to the ARM9 by WRAMCNT
0x04000000–0x04FFFFFFARM9 I/O portsDisplay, DMA, timers, keypad, IPC, gamecard, interrupts, maths, power, 3D
0x05000000–0x050007FFStandard palettes2 KiB: engine A and B, background and object
0x06000000–0x0607FFFFVRAM, engine A backgroundup to 512 KiB
0x06200000–0x0621FFFFVRAM, engine B backgroundup to 128 KiB
0x06400000–0x0643FFFFVRAM, engine A objectsup to 256 KiB
0x06600000–0x0661FFFFVRAM, engine B objectsup to 128 KiB
0x06800000–0x068A3FFFVRAM, LCDC-allocatedup to 656 KiB
0x07000000–0x070007FFOAM2 KiB: engines A and B
0x08000000–0x09FFFFFFGBA slot ROMup to 32 MiB
0x0A000000–0x0A00FFFFGBA slot RAMup to 64 KiB
0xFFFF0000–0xFFFF7FFFARM9 BIOS32 KiB, about 3 KiB used

ARM7

RangeNameWhat is there
0x00000000–0x00003FFFARM7 BIOS16 KiB
0x02000000–0x023FFFFFMain RAM4 MiB, shared with the ARM9
0x03000000–0x03007FFFShared WRAM0, 16 or 32 KiB, allocated to the ARM7 by WRAMCNT
0x03800000–0x0380FFFFARM7 WRAM64 KiB; shared WRAM is also mirrored at $037F8000 on both CPUs
0x04000000–0x04FFFFFFARM7 I/O portsTimers, DMA, keypad, IPC, gamecard, SPI, sound, interrupts
0x04800000–0x04807FFFWireless, wait state 032 KiB; 8 KiB RAM at $04804000
0x04808000–0x0480FFFFWireless, wait state 1I/O at $04808000
0x06000000–0x0603FFFFVRAM allocated as work RAMup to 256 KiB
0x08000000–0x09FFFFFFGBA slot ROMup to 32 MiB
0x0A000000–0x0A00FFFFGBA slot RAMup to 64 KiB

The address ranges are those the viewer draws; GBATEK gives the start and the size of each.

Main I/O registers

The viewer names many more registers than these (every register of both lists of GBATEK’s I/O maps that it prints, and the engine A and B background, DMA, timer and keypad registers, which have the names and layout of the Game Boy Advance’s registers). These are the ones a DS program uses to start up and to talk between the two processors.

AddressNameProcessorMeaning
0x04000000DISPCNTARM9LCD control, engine A
0x04000004DISPSTATbothGeneral LCD status
0x04000006VCOUNTbothVertical counter
0x04000130KEYINPUTbothKey status (0 = pressed)
0x04000180IPCSYNCbothIPC synchronize
0x04000184IPCFIFOCNTbothIPC FIFO control
0x04000188IPCFIFOSENDbothIPC send FIFO (write)
0x040001A0AUXSPICNTbothGamecard ROM and SPI control
0x040001A2AUXSPIDATAbothGamecard SPI data
0x040001A4ROMCTRLbothGamecard bus timing and control
0x040001A8CARD_COMMANDbothGamecard 8-byte command out
0x040001C0SPICNTARM7SPI bus control (firmware, touchscreen, power management)
0x040001C2SPIDATAARM7SPI bus data
0x04000204EXMEMCNTARM9External memory control
0x04000204EXMEMSTATARM7External memory status
0x04000208IMEbothInterrupt master enable
0x04000210IEbothInterrupt enable
0x04000214IFbothInterrupt request flags
0x04000240VRAMCNT_AARM9VRAM bank A control
0x04000247WRAMCNTARM9WRAM bank control
0x04000280DIVCNTARM9Division control
0x040002B0SQRTCNTARM9Square root control
0x04000300POSTFLGbothPost boot flag
0x04000301HALTCNTARM7Power-down control
0x04000304POWCNT1ARM9Graphics power control
0x04000304POWCNT2ARM7Sound and Wi-Fi power control
0x04000500SOUNDCNTARM7Sound control
0x04001000DISPCNT_BARM9LCD control, engine B
0x04100000IPCFIFORECVbothIPC receive FIFO (read)
0x04100010CARD_DATAbothGamecard 4-byte data in

The sizes are in the viewer’s table. The register names ending in “_B” are the engine B copies: that suffix is the viewer’s own, GBATEK lists engine B’s registers at 0x04001000 and up without one.