NFC Services

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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.

Only 1 session can be open for all of these services combined. Commands for each service are handled by the main-thread.

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 GetAdminInfo void s32 result, AdminInfo info Gets the AdminInfo of the amiibo.
0x04030000 9.3.0-X GetRegisterInfo void s32 result, RegisterInfo info Gets the RegisterInfo of the amiibo.
0x04040A40 9.3.0-X SetRegisterInfo RegisterInfo info s32 result Sets the RegisterInfo of the amiibo.
0x04050000 9.3.0-X DeleteRegisterInfo void s32 result Deletes the amiibo's registration info.
0x04060000 9.3.0-X DeleteApplicationArea void s32 result Deletes the amiibo's application area.
0x04070000 9.3.0-X ExistsApplicationArea void s32 result, bool exists Checks whether the amiibo's application area exists.
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"

Command header Available since system-version Description
0x00110100 ReadRawPages
0x001200C0 WriteRawPage

Some of these commands seems to be intended for use only on dev-units.

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"

Command header Available since system-version Description
0x00010000 Initialize
0x00020000 Shutdown
0x00030080 (unk0, unk1) ?
0x00040000 ?
0x000500C2 SendTagCommand
0x00060000 GetTagInfo
0x00070000 GetTagState maybe? Writes an output value to cmdreply[2].
0x00080000 Writes a handle to cmdreply[3].
0x00090000 Writes a handle to cmdreply[3].
0x000A0000 Unknown. Writes an output value to cmdreply[2].
0x000B0000 Unknown. Writes 0x60-bytes of output starting at cmdreply[2]. u16 +0 is the size of the data at +4, +2 is not initialized, u8 +3 is loaded from state, u32 +0x2C is loaded from state, and the data at +4 with the previously mentioned size is copied from state.
0x000C0040 (u32 outputsize) Writes output to static_buf_id=0, outputsize 1 is used when it's >=1.
0x000D0040 (u32 outputsize) Writes output to static_buf_id=0, outputsize 1 is used when it's >=1.
0x000E0080 (u8 unk, u32 outputsize) Writes output to static_buf_id=0, outputsize 2 is used when it's >=2.
0x000F0040 (u32 outputsize) Writes output to static_buf_id=0, outputsize 2 is used when it's >=2.
0x00100000 Unknown.
0x00110000 Unknown.
0x00120000 Unknown. Writes an output u32 to cmdreply[2].
0x00130000 Unknown. Writes an output u32 to cmdreply[2].

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. The mint process is the only known eShop-related process using this service(eShop-application and NIM-module don't use it). Used for NFC card payments in JPN eShop(the v16384 mint title is identical for USA/JPN besides programIDs in the NCCH header/exheader).

JPN eShop game "Megami Meguri" uses these same JPN NFC cards. The only accessible NFC service is nfcu.

NFC service "nfc:r"

This service has no known use.

NFC service "nfc:s"

Command header Available since system-version Description
0x00130102 SendTagCommand
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 Available since system-version Name Input Output Notes
0x00010040 Initialize u8 inputval s32 result
0x00020040 Shutdown u8 inputval s32 result
0x00030000 StartCommunication void s32 result
0x00040000 StopCommunication void s32 result
0x00050040 StartTagScanning u16 inval s32 result
0x00060000 StopTagScanning void s32 result
0x00070000 LoadAmiiboData
0x00080000 ResetTagScanState
0x00090002 UpdateStoredAmiiboData
0x000A0000 ??? void s32 result
0x000B0000 GetTagInRangeEvent(?) void s32 result, u32 copy handle descriptor, Handle event amiibo applet ignores value 'descriptor'. It doesn't even read it from the command buffer.
0x000C0000 GetTagOutOfRangeEvent(?) void s32 result, u32 copy handle descriptor, Handle event amiibo applet also ignores value 'descriptor' for this command.
0x000D0000 GetTagState void s32 result, u8 outval
0x000F0000 CommunicationGetStatus
0x00100000 GetTagInfo2
0x00110000 GetTagInfo
0x00120000 CommunicationGetResult
0x00130040 OpenAppData
0x00140384 InitializeWriteAppData
0x00150040 ReadAppData
0x00160242 WriteAppData
0x00170000 GetRegisterInfo
0x00180000 GetCommonInfo
0x00190000 GetAppDataInitStruct
0x001A0000 None No additional output.
0x001B0000 GetModelInfo
0x001C0040 9.6.0-X u8 inputval No additional output. ?
0x001D0040 9.6.0-X u32 inputval No additional output. ?
0x001E0040 9.6.0-X u8 inputval u8 outval at cmdreply[2]. ?
0x001F0080 10.0.0-X StartOtherTagScanning Used by JPN eShop app "Megami Meguri".
0x00200102 10.0.0-X SendTagCommand
0x00210000 10.0.0-X ? Used by JPN eShop app "Megami Meguri". This can only be used when initialized with type3, and when the TagState is 3.
0x00220000 10.0.0-X ? This can only be used when initialized with type3, and when the TagState is 3.

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 services error codes

Error-code Description
0xc8a17600 The current NFC tag state, or other NFC state, is invalid with the NFC command which was used.

Data Types

AdminInfo

Offset Size Description
0x00 0x08 Program ID (From the Wii U, 3DS or Switch title who created the application area)
0x08 0x04 App ID
0x0C 0x02 CRC32 Change Counter
0x0E 0x01 Flags (bit0 = amiibo initialized, bit1 = has application area, bit2/bit3 unknown)
0x0F 0x01 Unknown, hardcoded to 0x2
0x10 0x1 0xFF if there is no application area, related to the console of the application area game otherwise (0/2 = 3DS, 1 = Wii U, 3 = Switch)
0x11 0x07 Padding
0x18 0x28 Reserved

Note that this data is inferred from the corresponding Switch NFC data, there may be 3DS NFC specific differences as of yet unaccounted for.

RegisterInfo

Offset Size Description
0x00 0x60 Exported Mii Data (minus the AES-CCM used in the linked format)
0x60 0x16 Amiibo Name (NUL-Terminated)
0x76 0x01 Flags (bit0 = amiibo initialized, bit1 = has application area)
0x77 0x01 Font Region
0x78 0x04 Creation Date
0x7C 0x2C Reserved

This data originates from the Amiibo settings data stored under the encrypted NFC data.

CommonInfo

Offset Size Description
0x00 0x04 Last Write Date
0x04 0x02 Write Counter
0x06 0x07 Unknown
0x0D 0x01 This is byte[3] from NFC page[0x4].
0x0E 0x02 Application Area Size (hardcoded to 0xD8)
0x10 0x30 Reserved

This data originates from the Amiibo NFC data.

ModelInfo

Offset Size Description
0x00 0x02 Character ID
0x02 0x01 Character Variant
0x03 0x01 Amiibo Series
0x04 0x02 Model Number
0x06 0x01 Amiibo Type
0x07 0x2F Reserved

This data originates from the Amiibo NFC data.

Date

Offset Size Description
0x00 0x02 Year
0x02 0x01 Month
0x03 0x01 Day

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.

During NFC writing, the NFC data being written can become corrupted if the Amiibo figure is moved outside of range during writing. When this happens, this nfp_backup data can be used to restore a previous version of that data prior to the last failed write.

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?

NFC module versions

System version New3DS title-version Old3DS title-version Changes
9.6.0-X v4102 v4106 New3DS and Old3DS: the only changes regarding new commands is that new commands were added for the nfcu/nfcm command-set and new commands for an unknown cmd-handler were added. It's unknown if there's other changes.

Errors

Error code Description
0xC8A17600 This is returned when the current state is invalid for this command.
0xC8A17620 This is returned by NFC:OpenAppData when the appdata is uninitialized since NFC:InitializeWriteAppData wasn't used previously.
0xC8A17628 This is returned by NFC:GetAmiiboSettings when the amiibo wasn't setup by the amiibo Settings applet.
0xC8A17638 This is returned by NFC:OpenAppData when the input AppID doesn't match the actual Amiibo AppID.
0xC8C1760C Returned for HMAC-hash mismatch(data corruption), with HMAC-calculation input_buffer_size=0x34.
0xC8A17618 HMAC-hash mismatch with input_buffer_size=0x1DF(see here).
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