CONFIG9 Registers

Registers

Old3DS	Name	Address	Width	Used by
Yes	CFG9_SYSPROT9	0x10000000	1	Boot9
Yes	CFG9_SYSPROT11	0x10000001	1	Boot9
Yes	CFG9_RST11	0x10000002	1	Boot9
Yes	CFG9_DEBUGCTL	0x10000004	4
Yes	?	0x10000008	1	Boot9, Process9, TwlProcess9
Yes	CFG9_CARDCTL	0x1000000C	2	Process9
Yes	CFG9_CARDSTATUS	0x10000010	1	Process9
Yes	CFG9_CARDCYCLES0	0x10000012	2	Boot9, Process9
Yes	CFG9_CARDCYCLES1	0x10000014	2	Boot9, Process9
Yes	CFG9_SDSLOTCTL	0x10000020	2	Process9
Yes	?	0x10000100	2
No	CFG9_EXTMEMCNT9	0x10000200	1	NewKernel9
Yes	CFG9_MPCORECFG	0x10000FFC	4
Yes	CFG9_BOOTENV	0x10010000	4
Yes	CFG9_UNITINFO	0x10010010	1	Process9
Yes	CFG9_TWLUNITINFO	0x10010014	1	Process9

CFG9_SYSPROT9

CFG9_SYSPROT9 is used to permanently disable certain security-sensitive ARM9 memory areas until the next hard reset.

Bit	Description	Used by
0	Disables ARM9 bootrom(+0x8000) when set to 1, and enables access to FCRAM. Cannot be cleared to 0 once set to 1.	Boot9
1	Disables OTP area when set to 1. Cannot be cleared to 0 once set to 1.	NewKernel9Loader, Process9
31-2	Not used

On Old 3DS, NATIVE_FIRM reads CFG9_SYSPROT9 to know whether it has previously initialized the TWL console-unique keys using the OTP data. After setting the TWL console-unique keys, NATIVE_FIRM sets CFG9_SYSPROT9 bit 1 to disable the OTP area. In subsequent FIRM launches prior to the next reset, NATIVE_FIRM will see that the OTP area is disabled, and skip this step.

On New 3DS, the above is instead done by the Kernel9 loader. In addition to using the OTP data for initializing the TWL console-unique keys, the Kernel9 loader will generate the decryption key for NATIVE_FIRM. The final keyslot for NATIVE_FIRM is preserved, so that at a non-reset FIRM launch, the keyslot can be reused, since the OTP would then be inaccessible.

CFG9_SYSPROT11

Bit	Description	Used by
0	Disables ARM11 bootrom(+0x8000) when set to 1, and enables access to FCRAM. Cannot be cleared to 0 once set to 1.	Boot9
31-1	Not used

CFG9_RST11

Bit	Description	Used by
0	Presumably takes ARM11 out of reset. Cannot be set to 1 once it has been cleared.	Boot9
31-1	Not used

0x10000008

Bit	Description	Used by
1-0	?
3-2	AES related? Value 3 written after write to AES_CTL.	Boot9, Process9, TwlProcess9
31-4	Reserved

CFG9_CARDCTL

Bit	Description	Used by
1-0	Gamecard active controller select (0=NTRCARD, 1=?, 2=CTRCARD0, 3=CTRCARD1)	Process9
8	Enable gamecard eject IRQ, maybe?	Process9

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 CTRCARD0 will activate the register space at 0x10004000.
• Selecting CTRCARD1 will activate the register space at 0x10005000.

CFG9_CARDSTATUS

Bit	Description	Used by
0	Cartridge-slot empty (0=inserted, 1=empty)	Process9
3-2	?	Process9

CFG9_SDSLOTCTL

CFG9_SDSLOTCTL controls power and SD card detect?

Bit	Description	Used by
0-3	Powers on the SD card slot when unset. Each bit does the same? If bit 2 is set the 3DS hangs somewhere after SD init.	Process9
8	? This bit seems to do nothing.	Process9
9	Enables SD card detection?	Process9

CFG9_EXTMEMCNT9

This register is New3DS-only.

Bit	Description	Used by
0	Hide extended ARM9 memory (0=hidden, 1=shown)	Kernel9 (New3DS)
31-1	Reserved

CFG9_MPCORECFG

Identical to PDN_MPCORE_CFG.

CFG9_BOOTENV

This register is used to determine what the previous running FIRM was. Its value is kept following an MCU reboot. Its initial value (on a cold boot) is 0. NATIVE_FIRM sets it to 1 on shutdown/FIRM launch. LGY FIRM writes value 3 here when launching a TWL title, and writes value 7 when launching an AGB title.

NATIVE_FIRM will only launch titles if this is not value 0, and will only save the AGB_FIRM savegame to SD if this is value 7.

CFG9_UNITINFO

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

CFG9_TWLUNITINFO

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.