CONFIG9 Registers

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Old3DS Name Address Width Used by
Yes CFG_SYSPROT9 0x10000000 1 Boot9
Yes CFG_SYSPROT11 0x10000001 1 Boot9
Yes CFG_DEBUGUNIT 0x10000004 4
Yes CFG_CARDCONF 0x1000000C 2
Yes CFG_DEBUGGER 0x10000010 1
Yes ? 0x10000011 1
Yes ? 0x10000012 2
Yes ? 0x10000014 2
Yes ? 0x10000020 2
Yes ? 0x10000100 2
No CFG_EXTMEMCNT9 0x10000200 1 NewKernel9
Yes CFG_BOOTENV 0x10010000 4
Yes CFG_UNITINFO 0x10010010 1
Yes ? 0x10010014 1


Writing values to SYSPROT sets the specified bitmask. The ARM9 bootrom(+0x8000) is disabled by writing bit0. bit1 is used by NATIVE_FIRM to make sure console-unique TWL AES-keys are only set at hard-boot. It is not possible to set any other bits.

From disassembly of the New3DS process9, it appears that setting bit1 disables the 0x10012000+ region.


ARM11 bootrom (+0x8000) is disabled by writing bit0. It is not possible to set any other bits.


Bit Description
1-0 Gamecard active controller select (0=NTRCARD, 1=?, 2=CTRCARD1, 3=CTRCARD2)
8 ?

Depending on the gamecard controller that has been selected, one of the following gamecard registers will become active:

  • Selecting NTRCARD will activate the register space at 0x10164000.
  • Selecting CTRCARD1 will activate the register space at 0x10004000.
  • Selecting CTRCARD2 will activate the register space at 0x10005000.


This register is presumably New3DS-only. Only bit0 is writable: 0 = disable New3DS ARM9 memory at 0x08100000 size 0x80000, 1 = enable.

This bit is set by New3DS ARM9-kernel crt0.

The data in this extended memory doesn't change when disabling the memory, then re-enabling the memory. Reading this extended memory while disabled results in zeros.


Identical to PDN_MPCORE_CFG.


Initially this is value zero. NATIVE_FIRM writes value 1 here when a FIRM launch begins. The LGY FIRM writes value 3 here when handling PXI command 0x00020080(first TWL PXI command), it also writes value 7 here when handling PXI command 0x00030080(first AGB PXI command). This register can be read to determine what "mode" the system is running under: hard-boot, FIRM launch, or TWL/AGB FIRM.

0=Cold boot, 1=CTR, 3=TWL, 5=NTR, 7=AGB

It is unknown if this register controls anything.


This 8-bit register is value zero for retail, non-zero for dev/debug units.


In the console-unique TWL key-init/etc function the ARM9 copies the u8 value from REG_UNITINFO to this register.

This is also used by TWL_FIRM Process9.