NFC Services

The New3DS NFC module was added with 8.1.0-0_New3DS. The Old3DS NFC module was added with 9.3.0-X.

On New3DS NFC module uses the NFC hardware via the i2c::NFC and gpio:NFC services. On Old3DS NFC module communicates with a NFC peripheral via IR with the IRUSER service.

A total of 6 sessions can be open simultaneously for all of these services combined.

NFC services

NFC user service "nfc:u"

This is the NFC service used by regular applications, for the NFP API.

This was first seen in the Super Smash Bros eShop demo (only in the exheader, the demo doesn't actually use it), but at that time no system-module was available for NFC on CDN. The first regular application to use this service was Super Smash Bros, with the v1.0.5 game-update, which used the new 9.3.0-X command set.

NFC management service "nfc:m"

Command Header	Available since system-version	Name	Input	Output	Notes
0x040100C2	Unknown, <9.3.0-X	???	u32 unknownA, u32 unknownB, u32 unknownC, u32 (sizeof(*buffer) << 14 | 0x402), void * buffer	s32 result
0x04020000	9.3.0-X	???	void	s32 result, u32 unknownA[16]	Output seems to be a struct
0x04030000	9.3.0-X	???	void	s32 result, u32 unknownA[41]
0x04040A40	9.3.0-X	SetAmiiboSettings
0x04060000	9.3.0-X	???	void	s32 result
0x04070000	9.3.0-X	???	void	s32 result, u32 unknownA
0x04080000	9.3.0-X	???	void	s32 result, u32 unknownA
0x040C0000	9.3.0-X	?	None	s32 result	Among other things, this will eventually call the savedata writing code referenced in the below savedata section.
0x040D0000	9.3.0-X	???	void	s32 result
0x040E0000	9.3.0-X	???	void	s32 result, u32 unknownA, u32 unknownB	Again, amiibo applet ignores value unknownA.
0x040F0000	9.3.0-X	???	void	s32 result, u32 unknownA, u32 unknownB

This is used by the amiibo Settings applet. This service has the above commands, in addition to the command-set listed below.

NFC development service "nfc:dev"

This service seems to be intended for use only on dev-units(or at least some of the command(s)).

Unlike the New3DS NFC-module, at least some of these commands are stubbed in the Old3DS NFC-module(only returns an error).

NFC service "nfc:p"

This service is used by the mint library-applet, starting with 9.3.0-21. This service was added to the mint service-access-control list with 9.0.0-20.

NFC service "nfc:r"

This service has no known use.

NFC service "nfc:s"

Command header	Available since system-version	Description
0x00230000		This writes the following command request data to I2C, without reading any response: 10 20 00 01 01.
0x00240000		This writes the following command request data to I2C, without reading any response: 10 40 00 03 00 0F 01.

This service has no known use.

Unlike the New3DS NFC-module, at least some of these commands are stubbed in the Old3DS NFC-module(only returns an error).

"nfc:u" and "nfc:m" command set

There are at least two different revisions of the NFC module. First version was introduced on New3DS only with firmware 8.1.0-0_New3DS. Second version made its appearance with 9.3.0-X, on both Old3DS and New3DS.

These two versions are not interchangeable and not compatible, since the newer version uses a different command set and has no implemented commands from the older version. This does not introduce compatibility problems since no retail software used the NFC module, before the system titles added with 9.3.0-21 which use NFC.

9.3.0-X

Command Header	Name	Input	Output	Notes
0x00010040	nfcInit	u8 unknownA, can be 1 or 2.	s32 result	The two input values appear have the same result, except in addition NFC module will call some more functions with value 2. NFC module will eventually execute the savedata writing code referenced in the below savedata section with this command.
0x00020040	nfcStop	u8 unknownA	s32 result
0x00030000	???	void	s32 result
0x00040000	???	void	s32 result
0x00050040	???	u16 unknownA	s32 result
0x00060000	???	void	s32 result
0x00070000	???	void	s32 result
0x00080000	???	void	s32 result
0x00090002	UpdateStoredAmiiboData
0x000A0000	???	void	s32 result
0x000B0000	???	void	s32 result, u32 unknownA, u32 unknownB	amiibo applet ignores value unknownA. It doesn't even read it from the command buffer.
0x000C0000	???	void	s32 result, u32 unknownA, u32 unknownB	amiibo applet also ignores value unknownA for this command.
0x000D0000	???	void	s32 result, u8 unknownA
0x000F0000	???	void	u32 result, u32 unknownA
0x00100000	???	void	s32 result, u32 unknownA[24]
0x00110000	???	void	s32 result, u32 unknownA[8], u32 unknownB[2], u32 unknownC
0x00120000	???	void	s32 result, u32 unknownA
0x00130040	OpenAppData
0x00140384	InitializeWriteAppData
0x00150040	ReadAppData
0x00160242	WriteAppData
0x00170000	GetAmiiboSettings
0x00180000	GetAmiiboConfig
0x00190000	???	void	s32 result, u32 unknownA[8], u32 unknownB[4], u64 unknownC, u32 unknownD	Apparently output is a struct
0x001A0000		None	No additional output.
0x001B0000		None	0x36-byte output structure starting at cmdreply[2].

Pre-9.3.0-X

Pre-9.3.0-X command header	Command header starting with 9.3.0-X	Available since system-version	Description
0x00010000	?	8.1.0-0_New3DS	Initialize
0x00020000	?	8.1.0-0_New3DS	Shutdown
0x00030000	?	8.1.0-0_New3DS	GetNFCState. This writes an output u8 to cmdreply[2]: 0 = not initialized, 1 = just initialized, 5 = data transfer ready, ...
0x00040000	0x000B0000	8.1.0-0_New3DS	This writes an output handle to cmdreply[3].
0x00050000	0x000C0000	8.1.0-0_New3DS	This writes an output handle to cmdreply[3].
0x00060040	?	8.1.0-0_New3DS	(u8 input)
0x00070000	?	8.1.0-0_New3DS	The user process must setup the output-buffer hdr+ptr data @ TLS+0x180 when using this. cmdreply[2] = actual output data size?
0x00080100	?	8.1.0-0_New3DS	(<0x10-bytes starting at cmdreq[1]>)
0x00090000	?	8.1.0-0_New3DS
0x000A0000	?	8.1.0-0_New3DS	The user process must setup the output-buffer hdr+ptr data @ TLS+0x180 when using this.
0x000B0042	?	8.1.0-0_New3DS	(u32 size, ((Size<<14) | 2), inbufptr)
0x000C0044	?	8.1.0-0_New3DS	(u32 size, 0x20, <procid set by kernel>, ((Size<<14) | 0x402), inbufptr)
0x000D0040	?	8.1.0-0_New3DS	(u16 in)
0x000E0000	?	8.1.0-0_New3DS
0x000F00C2	?	8.1.0-0_New3DS	(u32 unk0, u32 unk1, u32 unk2, ((Size<<14) | 0x802), inbufptr)
0x00100040	?	8.1.0-0_New3DS	(u32 in)
0x00110040	?	8.1.0-0_New3DS	(u32 in)
0x00120040	?	8.1.0-0_New3DS	(u32 in)
0x00130000	?	8.1.0-0_New3DS	Writes an output u32 to cmdreply[2].
0x00140000	?	8.1.0-0_New3DS	This writes an output 0x30-byte struct starting at cmdreply[2].
0x00150000	0x00110000	8.1.0-0_New3DS	This writes an output 0x2C-byte struct starting at cmdreply[2].
0x00160000	?	8.1.0-0_New3DS
0x00170000	?	8.1.0-0_New3DS

NFC module savedata

• "/nfp_backup.dat" This contains raw data from the Amiibo NFC data pages. The filesize is 0x001fbd20-bytes. Certain service cmds will trigger writing to this savedata. This entire file is read during amiibo Settings startup, it's unknown what command(s) actually triggers that. It seems the Amiibo data here is updated each time the Amiibo NFC data is updated, and read each time the Amiibo NFC data is read. Data is written into this savedata when the Amiibo was never scanned on this system before. The data here is probably also updated when the scanned Amiibo NFC data doesn't match the data stored here.

nfp_backup.dat structure

Offset	Size	Description
0x0	0x20	Header
0x20	0x800	Amiibo data table header
0x7D20	0x21C	The NFC data for the first stored Amiibo is located here. This is the entire raw data from all 0x87 NFC data pages.

Header structure

Offset	Size	Description
0x0	0x8	Unknown, normally the following data? "00 00 02 00 02 00 00 00" (as little-endian u32s: 0x20000, 0x2)
0x8	0x14	Unknown, normally all-zero?
0x1C	0x4	Unknown. CRC32 / checksum maybe?

Amiibo data table header

This is an array with 0x40(?) entries, where the size of each entry is 0x20-bytes. Entry structure:

Offset	Size	Description
0x0	0x8	First 8-bytes from Amiibo NFC serial-number.
0x8	0x3	Unknown, normally zero?
0xB	0x2	u16 little-endian date value for when this Amiibo was initially written into this savedata, with the same format from here.
0xD	0xF	Unknown, normally zero?
0x1C	0x4	Unknown. CRC32 / checksum maybe?